valves

Gate Valves

Gate Valves

AdvantagesLimitations

High CapacityPoor Control

Tight ShutoffCavitate at low pressure drops

Low CostCannot be used for throttling

Little resistance to flow

Recommended Uses

Fully open/closed, non-throttling

Infrequent operation

Minimal fluid trapping in line

Applications

Oil

Gas

Air

Slurries

Heavy liquids

Steam

Noncondensing gases

Corrosive liquids

Best Suited For:

Frequent on-off service

Processes where "instantly" large flow is needed (ie. safety systems or cooling water systems)

BALL VALVES

Ball Valves

AdvantagesLimitations

Low costPoor throttling characteristics

High capacityProne to cavitation

Low leakage and maintenance

Tight sealing with low torque

Recommended Uses

Fully open/closed, limited-throttling

Higher temperature fluids

Applications

Most liquids

High Temperatures

Slurries

Best Suited For:

Frequent on-off service

Processes where "instantly" large flow is needed (ie. safety systems or cooling water systems)

Liquid level or flow loops

Systems where the pressure drop across the valve is expected to remain fairly constant (ie. steady state systems)

Butterfly Valves

Butterfly Valves

AdvantagesLimitations

Low cost and maintenanceHigh torque required for control

High capacityProne to cavitation at lower flows

Good flow control

Low pressure drop

Recommended Uses

Fully open/closed or throttling services

Frequent operation

Minimal fluid trapping in line

Applications

Liquids

Gases

Slurries

Liquids with suspended solids

Best Suited For:

Frequent on-off service

Processes where "instantly" large flow is needed (ie. safety systems or cooling water systems)

Processes where large changes in pressure drop are expected

Processes where a small percentage of the total pressure drop is permitted by the valve

Temperature and pressure control loops

Diaphragm or Metal Bellows Type

Soft-Seated, Pilot Operated-Low Pressure (Diaphragm or Metal Bellows Type)

AdvantagesLimitations

Good operation at very low set pressure (3-inch wc)Not recommended for polymerizing type services without pilot purge

Excellent seat tightness before relievingVital to match soft goods with process conditions

Excellent reseat tightness after relievingLimited high pressure setting (about 50 psig)

Ease of setting and adjusting set pressure and blowdownLiquid service limitations

Pop or modulating action availableNot generally used in dirty services without options to eliminate introduction of particles into the pilot

Adaptable for remote pressure sensingMore wetted parts exposed to fluids. Exotic materials can result in an expensive valve.

Short blowdown obtainable

Set pressure can be field tested while in service

Remote unloading available

Lift not effected by back pressure (when pilot discharges to atmosphere or is balanced)

Fully open at set pressure with no overpressure

In-line maintenance of main valve

Typical applications:Chemical, Fossil Power Plants, Pharmaceutical, Mining, Nuclear Power Plants, Water treatments...

Globe Valves

A globe valve is a linear motion valve used to stop, start, and regulate fluid flow.

Globe Valves

AdvantagesLimitations

Efficient throttlingHigh pressure drop

Accurate flow control valvesMore expensive than other valves

Available in multiple ports

Recommended Uses

Throttling service / flow regulation

Frequent operation

Applications

Liquids

Vapors

Gases

Slurries

Corrosive Substances

Best Suited For:

Liquid level or flow loops

Systems where the pressure drop across the valve is expected to remain fairly constant (ie. steady state systems)

Processes where large changes in pressure drop are expected

Processes where a small percentage of the total pressure drop is permitted by the valve

Temperature and pressure control loops

Pressure Relief Valves

Metal-to-Metal Seated, Pilot Operated - Pressure Relief Valves

AdvantagesLimitations

Excellent seat tightness before relievingOnly pop action available

Excellent seat tightness after reclosingPressure limited to 1200 psig

Ease of setting and adjusting set pressure and blowdownTemperature limited to 1000F

Adaptable for remote pressure sensing

Short blowdown obtainable

Set pressure can be field-tested while in service

Excellent chemical and temperature compatibility

Dual pilot option allows in-service pilot replacement

Check Valve

A check valve, clack valve, non-return valve or one-way valve is a mechanical device, a valve, which normally allows fluid (liquid or gas) to flow through it in only one direction.Advantages Protection of any item of equipment that can be affected by reverse flow, such as flowmeters, strainers and control valves. To check the pressure surges associated with hydraulic forces, for example, waterhammer. These hydraulic forces can cause a wave of pressure to run up and down pipework until the energy is dissipated. Prevention of flooding. Prevention of reverse flow on system shutdown. Prevention of flow under gravity. Relief of vacuum conditions.Applications

Boiler feedlines

Steam traps

Hot water circuits

Vacuum breakers

Blending

THE NEEDLE VALVEIt is called needle valve due to the shape of the closure member. It consists on a threaded stem with a conical end.This is simply a variation of the Globe valve and, as its name implies consists of a narrow, tapered plug and port arrangement. The needle valve is, in itself, small in size and is used for very fine and normally manual, control of fluid flow.

UnitAdvantagesDisadvantages

Needle valveIt gives good flow control;

It can have very high pressure ratings.It causes a high pressure drop &

presents a greater risk of clogging due to entrained solids.

Types of Pumps Deep Piston Pump

This is the same as for shallow except the pump cylinder is attached to the bottom of the drop pipe. As the piston moves up and down, it pumps water up through the drop. pipe. Deep-well piston pumps can lift water from 600 feet. Double acting piston pumps can pump 65% more water with only 15% more horsepower. Advantages and disadvantages for this type are the same as for shallow piston pumps.

Centrifugal Pumps :

Out let of centrifugal pump

The operating principle of the centrifugal pump can be illustrated by considering the effect of swinging a bucket of water around in a circle of water at the end of a rope. The force pushing the water against the bottom of the bucket is centrifugal force. If a hole were cut in the bottom of the bucket, water would flow through the hole. Further, if an intake pipe where connected to an air tight cover over the top of the bucket, the flow of water out the hole would result in the evelopment of a partial vacuum inside the bucket. This vacuum would bring water into the bucket from a source at the other end of the intake. In this way, continuous flow from the source and out through the bucket would be established. In terms of real centrifugal pumps, bucket and lid correspond the pump casing, the hole and intake pipe correspond to the intake and discharge of the pump, and the rope and arm perform Centrifugal pumps can be used for depths up to about 15 feet. They are considered very efficientfor capacities of over 50 gpm and pressures of less than 65 pounds per square inch. They are con- sidered ideal for use as a booster pump to send water from a well pump to storage or to a distribution system. Advantages Produces a smooth and even flow. Some types pump some sand. Centrifugal pumps are also usually reliable with a good service life (1). Disadvantages Centrifugal pumps lose their prime easily, and their efficiency depends upon on operating under design heads and speed (1) Pump Impeller Types

Impellers of pumps are classified based on the number of points that the liquid can enter the impeller and also on the amount of webbing between the impeller blades.Impellers can be either single suction or double-suction. A single-suction impeller allows liquid to enter the center of the blades from only one direction. A double-suction impeller allows liquid to enter the center of the impeller blades from both sides simultaneously. The illustration below shows simplified diagrams of single and double-suction impellersImpellers can be open, semi-open, or enclosed. The open impeller consists only of blades attached to a hub. The semi-open impeller is constructed with a circular plate (the web) attached to one side of the blades. The enclosed impeller has circular plates attached to both sides of the blades. Enclosed impellers are also referred to as shrouded impellers. Figure 5 illustrates examples of open, semi-open, and enclosed impellers.

The impeller sometimes contains balancing holes that connect the space around the hub to the suction side of the impeller. The balancing holes have a total cross-sectional area that is considerably greater than the cross-sectional area of the annular space between the wearing ring and the hub. The result is suction pressure on both sides of the impeller hub, which maintains a hydraulic balance of axial thrust.There are two basic types of impellers. volute and turbine. Turbine impellers are surrounded by diffuser vanes which provide gradually enlarging passages in which the velocity of the water is slowly reduced thus transforming the velocity head into pressure head. Volute impellers are characterized by having no diffusion vanes. Instead, its impeller is housed in a case which isspiral shaped and in which the velocity of the water is reduced upon leaving the impeller, with resultant increase in pressure.Turbine Multistage Turbine Multistage pumps operate under the same principle as the turbine-impeller centrifugal pump except there are one or more impellers mounted close together on a vertical shaft. The bowls are positioned below the water level, and the discharge pipe and shaft extend to a motor on the surface. These pump are usually used for high capacity from deep wells - up to 1500 feet deep. The capacity and pressure depends on design, diameter, and number of impellers. Advantages Produces smooth, even flow and is easy to frost proof. The long drive shaft requires a straight and vertical well casing. Disadvantages To repair the pump, it must be pulled from the well.Submersible Multistage Pumps This type operates like a centrifugal pump except that several impellers are mounted together on a vertical shaft. The impellers and motor are in a housing which is positioned below the waterlevel. Submersible pumps can lift from up to 1000 feet deep. The pump capacity and pressure depends on diameter, speed, and number of impellers. Advantages Submersible pumps produce a smooth and even flow and are easy to frost proof. They also have a short pump shaft to the motor. Disadvantages This pump type is easily damaged by sand in the water, and repair requires pulling the pump out of the well. Helical Rotor Pumps The helical rotor pump operates like an auger to force water up through the pump. The motor and auger are in a housing under the water level. The capacity of the pump depends on the design of the rotor. Water can be pumped from depths of up to 1000 feet and well casings can be 4 inches or larger in diameter. Advantages Helical rotors produce a smooth and even flow, and they are easy to frost proof. In addition, there is a short pump shaft to the motor. Sand also damages these pumps less than any other type. Disadvantages Repair of the pump requires pulling it from the well.

SEWAGE PUMPING STATIONS 1.GENERAL 1.1 Flooding Sewage pumping structures and electrical and mechanical equipment shall be protected from physical damage by the 100-year flood. Sewage pumping stations shall remain operational and accessible and shall not be inundated by the 100-year flood (hurricane flood surges excepted). Design consideration shall be given to groundwater elevations and the risk of floating dry wells or empty wet wells. 1.2 Accessibility The station shall be readily accessible by maintenance vehicles during any weather. The station shall be inaccessible to the general public (by a locked fence or enclosure, by built underground, etc.). 1.3 Grit Where it is necessary to pump sewage prior to grit removal, the design of the wet well and pump station piping shall receive special consideration such as grit removal facilities to avoid operational problems from the accumulation of grit. 2. DESIGN 2.1 Type Sewage pumping stations may be wet/dry well, suction lift, or submersible. Screw type lift stations may also be allowed. All equipment shall be designed specifically for the handling of raw or pretreated sewage, as appropriate. 2.2 Structures 2.2.1 Separation Dry wells, including their superstructure, shall be completely separated from the wet well. 2.2.2 Equipment Removal Provision shall be made to facilitate removal of pumps, motors, and other equipment. 2.2.3 Access Suitable and safe means of access for persons wearing self-contained breathing apparatus shall be provided to dry wells, and to wet wells containing either bar screens or mechanical equipment requiring inspection or maintenance. For built-in-place pump station dry wells, a stairway with rest landings shall be provided at vertical intervals not to exceed 12 feet (3.7 m). For factory-built pump station dry wells over 15 feet (4.6 m) deep, a rigidly fixed landing shall be provided at vertical intervals not to exceed 10 feet (3.0 m). Where a landing is used, a suitable and rigidly fixed barrier shall be provided to prevent an individual from falling past the intermediate landing to a lower level. Where acceptable to the Department, an elevator may be used in lieu of landings in a factory-built station, provided emergency access is included. Reference should be made to applicable safety codes which, if they are more stringent than provided herein or in the specifications, shall govern. The provisions of Section 46.5 also apply. 2.2.4 Construction Materials Due consideration shall be given to the selection of materials because of the presence of hydrogen sulfide and other corrosive gases, greases, oils, and other constituents frequently present in sewage. 2.3 Pumps and Pneumatic Ejectors 2.3.1 Multiple Units Multiple pumps or pneumatic ejectors shall be provided. A minimum of three (3) pumps should be provided for stations handling flows greater than 1 MGD (3800 m 3/d). Units should be designed to fit actual flow conditions and shall be of such capacity that with any one unit out of service the remaining units will have capacity to handle maximum anticipated sewage flows. 2.3.2 Protection Against Clogging All units shall be designed specifically for the handling of the types of sewage they will be subjected to. Pumps handling sanitary sewage from 30 inch (76 cm) or larger diameter sewers shall be preceded by readily accessible bar racks to protect the pumps from clogging or damage. Bar racks should have clear openings not exceeding 22 inches (6 cm). Where a bar rack is provided, a mechanical hoist shall also be provided. Where the size of the installation warrants, mechanically cleaned and/or duplicate bar racks shall be provided. Appropriate protection from clogging should also be considered for small pumping stations. 2.3.3 Pump Openings Except where grinder pumps or septic tank effluent pumps are used, pumps shall be capable of passing spheres of at least 3 inches (8 cm) in diameter, and pump suction and discharge piping shall be at least 4 inches (10 cm) in diameter. See Section 37.2 for the size of force mains. 2.3.4 Priming The pump shall be so placed that under normal operating conditions it will operate under a net positive suction head, except as specified in Sections 33 and 34. 2.3.5 Electrical Equipment Electrical systems and components (e.g., motors, lights, cables, conduits, switchboxes, control circuits, etc.) in raw sewage wet wells, or in enclosed or partially enclosed spaces where hazardous concentrations of flammable gases or vapors may be present, shall be designed for safe use under such conditions to the extent practicable. In addition, equipment located in the wet well shall be suitable for use under corrosive conditions. Each cable shall be provided with watertight seal (and separate strain relief for flexible cables). A fused disconnect switch located above ground shall be provided for all pumping stations. When such equipment is exposed to weather, it shall meet the requirements of weatherproof equipment (NEMA 3R or 4). Lightning arresters and phase protection (for 3-phase motors) shall be provided. GFCI protection shall be provided for all outlets. For each location requiring electrical power, the consulting engineer shall provide a written description of the type of power needed (voltage, amperage, phase, etc.) and shall give his written assurance (either in the P/S or in a separate letter) that the proper power will be available and when it will be available at each site. Phase protection and phase loss warning shall be provided for 3-phase power. Phase protection shall prevent automatic equipment restarting attempts upon power restoration until all three phases are restored. 2.3.6 Intake Each pump should have an individual intake. Wet well design should be such as to avoid turbulence near the intake. Intake piping should be as straight and short as possible. 2.3.7 Dry Well Dewatering A sump pump equipped with dual check valves shall be provided in the dry wells to emove leakage or drainage, with the discharge located above the maximum high water level in the wet well. A connection to the pump suction is also recommended as an auxiliary feature. Water ejectors connected to a potable water supply shall not be . All floor and walkway surfaces should have an adequate slope to a point of provided drainage. Pump seal water shall be piped to the sump. Shallow valve pits, etc. may be gravity drained to the wet well as allowed in Section 34.4. 2.3.8 Pumping Rates The pumps and controls of main pumping stations, and especially the pumping station(s) to the treatment works or operated as part of the treatment works, should be capable of discharging sewage at approximately its rate of delivery to the pump station. Wet well , influent flow rates, and pumping capacity shall all be balanced to ensure sufficient capacity without excessive pump run time or detention time in the wet well. See Section 2.4 Controls 2.4.1 Type Control systems shall be of the transducer, air bubbler, encapsulated float or flow measuring type. Float-tube control systems or existing stations being upgraded may be approved. 2.4.2 Location The control system shall be located away from the turbulence of incoming flow and pump suction. 2.4.3 Alternation Provisions should be made to automatically alternate the pumps in use. Provisions shall be made for simultaneous operation of multiple units when flow conditions warrant. Generally, when multiple pumps are operating and the water level is falling, the pumps should not be sequenced off, but all on pumps should remain on until the lowest control level is reached, then all pumps should switch off together.

2.5 Valves 2.5.1 Suction Line Suitable shutoff valves shall be placed on the suction line of each pump except on submersible and vacuum-primed pumps. 2.5.2 Discharge Line Suitable shutoff and check valves shall be placed on the discharge line of each pump discharging into a pressurized header. The check valve shall be located between the shutoff valve and the pump. Check valves shall be suitable for the material being handled. Except for pre-manufactured stations, check valves shall not be placed on the vertical portion of discharge piping. Valves shall be capable of withstanding normal pressure and water hammer. All shutoff and check valves shall be operable from floor level and accessible for maintenance. External levers should be provided on swing check valves. 2.5.3 Location Valves shall not be located in the wet well, except as provided in Section 34.4. 2.6 Wet Wells 2.6.1 Divided Wells Consideration should be given to dividing the wet well into multiple sections, properlyinterconnected, to facilitate repairs and cleaning. 2.6.2 Size The wet well size and control setting shall be appropriate and in accordance with the pump manufacturer's recommendations to avoid heat buildup in pump motor due to frequent starting and to avoid septic conditions due to excessive detention time. No more than ten (10) pump starts per hour should be allowed. For duplex stations, the design wet well volume in gallons may be calculated as 15 min. x influent (gpm) / 8. 2.6.3 Floor Slope The wet well floor shall have a minimum slope of one to one to the hopper bottom. The horizontal area of the hopper bottom shall be not greater than necessary for proper installation and function of the inlet. 2.7 Ventilation Adequate ventilation shall be provided for all pump stations. There shall be no interconnection between the wet well and dry well ventilation systems. 2.7.1 Ventilation in Pump Stations Less Than 350 gpm or Any Submersible Type Not Requiring Entry. At a minimum, passive screened vent pipes shall be provided. Mechanical ventilation as described below is recommended. 2.7.2 Ventilation in Pump Station of 350 gpm or Larger Where the pump pit is below the ground surface, mechanical ventilation is required, so arranged as to independently ventilate the dry well and the wet well if screens or mechanical equipment requiring maintenance or inspection are located in the wet well. In pits over 15 feet (4.6 m) deep, multiple inlets and outlets are desirable. Damper should not be used on exhaust or fresh air ducts and fine screens or other obstructions in air ducts should be avoided to prevent clogging. Switches for operation of ventilation equipment should be marked and located conveniently. All intermittently operated ventilating equipment shall be interconnected with the respective pit lighting systems, which shall override any automatic controls. Consideration should be given also to automatic controls where intermittent operation is used. The fan wheel should be fabricated from non-sparking material. Consideration should be given to installation of automatic heating and/or dehumidification equipment. 2.7.2.1 Wet Wells Ventilation may be either continuous or intermittent. Ventilation, if continuous, shall provide at least 12 complete air changes per hour; if intermittent, at least 30 changes per hour. Air shall be forced into the wet well rather than exhausted from the wet well. 2.7.2.2 Dry Wells Ventilation may be either continuous or intermittent. Ventilation, if continuous, shall provide at least 6 complete air changes per hour; if intermittent, at least 30 complete air changes per hour. Air should be forced in, rather than exhausted. 2.8 Flow Measurement Suitable devices for measuring sewage flow and/or run time should be considered at all pump stations. 2.9 Water Supply There shall be no physical connection between any potable water supply and a sewage pumping station that under any conditions might cause contamination of the potable water supply. If a potable water supply is brought to the station, it should comply with conditions stipulated under Section 46.2. 3. SUCTION LIFT PUMPS Suction lift pumps shall be of the self-priming or vacuum-priming type and shall meet the applicable requirements of Section 32. Suction lift pump stations using dynamic suction lifts exceeding the limits outlined in the following sections may be approved upon submission of factory certification of pump performance and detailed calculations indicating satisfactory performance under the proposed operating conditions. Such detailed calculations must include static suction lift as measured from "lead pump off" elevation to center line of pump, friction and other hydraulic losses of the suction piping, vapor pressure of the liquid, altitude correction, required net positive suction head, and a safety factor of at least 6 feet (1.8 m). The pump equipment compartment shall be above grade or offset and shall be effectively isolated from the wet well to prevent the humid and corrosive sewer atmosphere from entering the equipment compartment. Wet well access shall not be through the equipment compartment. The combined total of dynamic suction lift at the "pump off" elevation and required net positive suction head at design operating conditions shall not exceed 22 feet. Suction lift pumps shall be equipped with an air release valve in the discharge piping. Drainage from the air release valve shall be piped back to the wet well at elevation higher than the maximum wet well water level. 3.1 Self-Priming Pumps Self-priming pumps shall be capable of rapid priming and repriming at the "lead pump on" elevation. Such self-priming and repriming shall be accomplished automatically under design operating conditions. Suction piping should not exceed the size of the pump suction and shall not exceed 25 feet (7.6 m) in total length. Priming lift at the "lead pump on" elevation shall include a safety factor of at least 4 feet (1.2 m) from the maximum allowable priming lift for the specific equipment at design operating conditions. 3.2 Vacuum-Priming Pumps Vacuum-priming pump stations shall be equipped with multiple vacuum pumps capable of automatically and completely removing air from the suction lift pump. The vacuum pumps shall be adequately protected from damage due to sewage. 4. SUBMERSIBLE PUMP STATIONS 4.1 Construction Submersible pumps and motors shall be designed specifically for raw sewage use, including totally submerged operation during a portion of each pumping cycle and shall meet the requirements of the National Electrical Code for such units. An effective method to detect shaft seal failure or potential seal failure shall be provided, and the motor shall be of squirrel-cage type design without brushes or other arc-producing mechanisms. 4.2 Pump Removal Submersible pumps shall be readily removable and replaceable without entering, dewatering, or manually disconnecting any piping in the wet well. 4.3 Electrical 4.3.1 Power Supply and Control Electrical supply, control and alarm circuits shall be designed to provide strain relief and to allow disconnection from outside the wet well. Terminals and connectors shall be protected from corrosion by location outside the wet well or by the use of watertight seals. If located outside, weatherproof equipment shall be used. 4.3.2 Controls The motor control center shall be located outside the wet well, be readily accessible, and be protected by a conduit seal or other appropriate measures meeting the requirements of the National Electrical Code to prevent the atmosphere of the wet well from gaining access to the control center. The seal shall be so located that the motor may be removed and electrically disconnected without disturbing the seal. 4.3.3 Power Cord Pump motor power cords shall be designed for flexibility and serviceability under extra hard usage conditions and shall meet the requirements of the National Electrical Code standards for flexible cords in wastewater pump stations. Ground fault circuit interruption protection shall be used to de-energize the circuit in the event of any electrical failure in the cable. Power cord terminal fittings shall be corrosion-resistant and constructed in a manner to prevent the entry of moisture into the cable, shall be provided with strain relief appurtenances, and shall be designed to facilitate field connecting. 4.4 Valves Valves required under Section 32.5 shall be located in a separate valve pit. Accumulated water shall be drained to the wet well or to the soil. Sewage leaking into the valve pit shall not be drained to the soil. If the valve pit is drained to the wet well, an effective method shall be provided to prevent sewage from entering the pit during surcharged wet well conditions. Check valves that are integral to the pump may be located in the wet well provided that the valve can be removed in accordance with Section 34.2. 5. ALARM SYSTEMS Alarm systems SHALL be provided for all pumping stations. The alarm shall be activated in cases of POWER FAILURE, high water elevation, pump failure, phase loss, or any cause of pump station malfunction. Alarms for major pumping stations should be telemetered, including identification of the alarm conditions, to a municipal facility that is manned 24 hours a day. If such a facility is not available and 24-hour holding capacity is not provided, the alarm should be telemetered to city offices during normal working hours and to the home of the person(s) in responsible charge of the lift station during off-duty hours. 6. EMERGENCY OPERATION Pumping stations and collection systems shall be designed to prevent or minimize bypassing of raw, diluted, or partially treated sewage. For use during possible periods of extensive power outages, mandatory power reductions, or uncontrolled storm events, consideration should be given to providing storage/detention tanks or basins, which shall be made to drain to the station wet well. Where such overflows affect public water supplies, shellfish production, or water used for culinary or food processing purposes, a storage/detention basin or tank shall be provided having 24-hour detention capacity at the anticipated overflow rate. 6.1 Overflow Prevention Methods A satisfactory method shall be provided to prevent or minimize overflows in the event of station failure. The following methods should be evaluated on an individual basis (the choice should be based on least cost and least operational problems of the methods providing an acceptable degree of reliability): a. Storage capacity, including trunk sewers, for retention of 24-hour design return wet weather flows (storage basins must be designed to drain back into the wet well or collection system after the flow recedes); b. Other methods meeting the requirements of Section 46.1.1 6.2 Equipment Requirements 6.2.1 General The following general requirements shall apply to all internal combustion engines used to drive auxiliary pumps, service pumps through special drives, or electrical generating equipment. 6.2.1.1 Engine Protection The engine must be protected from operating conditions that would result in damage to equipment. Unless continuous manual supervision is provided, protective equipment shall be capable of shutting down the engine and activating an alarm on site and as provided in Section 35. Protective equipment shall monitor for conditions of low oil pressure and overheating, except that oil pressure monitoring is not required for engines with splash lubrication. Oil level monitoring for such engines is recommended. 6.2.1.2 Size The engine shall have adequate rated power to start and continuously operate under all connected loads. 6.2.1.3 Fuel Reliability and ease of starting, especially during cold weather conditions, should be considered in the selection of the type of fuel. Above ground liquid fuel tanks exceeding 660 gallon single tank capacity or 1320 gallon total capacity require a Spill Prevention Control and Countermeasure (SPCC) Plan and containment in accordance with 40 CFR 112. It is recommended that all above ground liquid fuel tanks have spill containment devices with a minimum capacity equal to the largest tank's volume plus an allowance for precipitation. 6.2.1.4 Engine Ventilation The engine shall be located above grade with adequate ventilation of fuel vapors and exhaust gases. 6.2.1.5 Routine Start-up All emergency equipment shall be provided with instructions indicating the need for regular starting and running of such units at full loads. 6.2.1.6 Protection of Equipment Emergency equipment shall be protected from damage at the restoration of regular electrical power. In addition, emergency generating equipment shall be provided with a means of disconnecting such equipment from the regular incoming power source during emergency operating conditions in order to protect others who may be in contact with the failed power system. In the case of automatic systems, such disconnect shall also be automatic. In the case of manual systems, the load transfer switch or connection shall be designed such that it is impossible to connect the auxiliary power source to the primary power source. 6.2.2 Engine-Driven Pumping Equipment Where permanently-installed or portable engine-driven pumps are used, the following requirements in addition to general requirements shall apply. 6.2.2.1 Pumping Capacity Engine-driven pump(s) shall meet the design pumping requirements unless storage capacity is available for flows in excess of pump capacity. Pumps shall be designed for anticipated operating conditions, including suction lift if applicable.

6.2.2.2 Operation Unless continuous manual supervision is provided, the engine and pump shall be equipped to provide automatic start-up and operation of pumping equipment. Provisions shall also be made for manual start-up. 6.2.2.3 Portable Pumping Equipment Where part or all of the engine-driven pumping equipment is portable, sufficient storage capacity to allow time for detection of pump station failure and transportation and hook up of the portable equipment shall be provided. This is likely to be 24 hours. A riser from the force main with quick-connect coupling and appropriate valving shall be provided to hook up portable pumps. 6.2.3 Engine-Driven Generating Equipment Where permanently-installed or portable engine-driven generating equipment is used, the following requirements in addition to general requirements shall apply. 6.2.3.1 Generating Capacity Generating unit size shall be adequate to provide power for pump motor starting current and for lighting, ventilation, and other auxiliary equipment necessary for safe and proper operation of the lift station. The operation of only one pump during periods of auxiliary power supply must be justified. Such justification may be made on the basis of maximum anticipated flows relative to single-pump capacity, anticipated length of power outage, and storage capacity. Special sequencing controls shall be provided to start pump motors unless the generating equipment has capacity to start all pumps simultaneously with auxiliary equipment operating. 6.2.3.2 Operation Unless continuous manual supervision is provided, provisions shall be made for automatic and manual start-up and load transfer. The generator must be protected from operating conditions that would result in damage to equipment. Provisions should be considered to allow the engine to start and stabilize at operating speed before assuming the load. Where manual start-up and transfer is justified, storage capacity must meet the requirements of Section 36.2.3.3. 6.2.3.3 Portable Generating Equipment Where portable generating equipment or manual transfer is provided, sufficient storage capacity to allow time for detection of pump station failure and transportation and connection of generating equipment shall be provided. The use of special electrical connections and double throw switches is recommended for connecting portable generating equipment. 7. FORCE MAINS 7.1 Velocity At design average flow a velocity of at least 2 fps (0.61 m/s) shall be maintained. 7.2 Size Except where grinder pumps or septic tank effluent pumps are used, force mains shall be at least 4 inches in diameter. See Section 32.3.3 for pump sizes. 7.3 Depth The requirements of Section 23.2 shall apply. 7.4 Air and Vacuum Relief Valves Automatic air relief valves shall be placed as needed (at high points) in the force main to prevent air locking. Vacuum relief valves may also be necessary. 7.5 Termination Force mains should enter the gravity sewer system at a point not more than 2 feet (61 cm) above the flow line of the receiving manhole.

7.6 Design Pressure The force main and fittings, including reaction blocking, shall be designed to withstand normal pressure and pressure surges (water hammer). 7.7 Special Construction Force main construction near streams or used for aerial crossings shall meet applicable requirements of Sections 27 and 28. 7.8 Design Friction Losses Friction losses through force mains shall be based on the Hazen and Williams formula or other acceptable method. When the Hazen and Williams formula is used, the following values for "C" shall be used for design. Smooth plastic or smooth lined iron or steel - 130 to 140 Unlined iron or steel - 100 All other - 120 (maximum) When initially installed, force mains will have a significantly higher "C" factor. The higher "C" factor should be considered only in calculating maximum power requirements. 7.9 Separation from Water Mains The requirements of Section 28.3 shall be met for all sewage force mains. 7.10 Identification Where force mains are constructed of material which might cause the force main to be confused with potable water mains, the force main should be appropriately identified. .Sewer Appurtenances1. Manholes They are used for inspection & cleaning. They placed when: 1. Intervals between manholes: 90-150m (300-500ft.) 2. Change in direction. 3. Change in pipe slope. 4. Change in pipe size. - For total depth < 4m (12ft) 250mm (10) thick brick wall. For any additional 2m depth additional 125mm thick. - Concrete walls are often used in Iraq, Figs.(1). - Manholes bottom: Upper surface sloped toward the open channel, why? Channel depth should be equal to pipe diameter to prevent sewage from spreading over manhole bottom, & odors result. Changes of direction are made in channels.

- Drop manhole: What is the Difference Between a Drop Manhole and a Regular Manhole?

A drop manhole is used in areas with a steep slope when one or more of the inlet pipes has an invert elevation significantly higher than the invert of the outlet pipe. Typically the invert elevation of the "stop" end of the inlet pipe is set to the invert elevation of the manhole. However, in the case of a drop manhole, the stop invert of the pipe is not set to the manhole invert elevation but is at a significantly higher elevation.

The following illustration shows a drop manhole.Figure 15-1: Drop Manhole

It is a join between submain & a deeper sewer. It is used when the drop between two sewers 0.6m (2ft). - Manhole opening Cast iron frame & cover 500-600mm (20-24). - Manholes in large sewers 1520mm (60), These sewers can be entered for inspection & need fewer manholes- Manhole cover & frame

For heavy city traffic 340kg (750Lb) Light city traffic 245kg (540Lb) Suburban traffic 150-180kg (325-400Lb) Foot traffic 70kg (150Lb) Covers shall be roughened to prevent slipperiness. Perforated covers should not be used for sanitary sewers. Ventilation should be done by stacks, not by openings. Opening disadvantages: permitting rainwater, sand & grit to enter sewers. Ladder: steps made of epoxy coated cast iron. 2. Cleanouts: They may be used instead of manholes as an economy measure. They permit flushing the sewer with a fire hose & rods mat also be inserted to clear heavy obstructions. Some cities not permit cleanouts. They may be used at head end of small sewers.

They are openings into a storm or combined sewer for entrance of storm runoff. They placed at: 1. Street intersections, they located near the intersection but not in it, why? a Crosswalks will not flooded. b. Inlets will not subjected to traffic wear & damage. 2. Midpoints of the blocks for > 150m (500ft) long. Locally 40m, why? Inlets connected to: 1. A manhole, or 2. Through Ys at nearest points. Design of curb- opening inlet Curb- opening inlet

Capacity determination by using Manning formula, Q = K (z/n) * S1/2* y8/3 Where: Q = gutter flow, z = reciprocal of transverse slope of gutter bottom, n = 0.015, S = gutter slope, y = water depth in gutter at curb line, K = constant = (units) = 22.6 (m/min, m) = 0.56 (ft3/s, ft) 4. Catch Basins:Catch basin is an inlet with a basin which allows debris to settle out. Outlet pipe is trapped in order to prevent escape of odors from sewer & causes retention of floating matter. It is limited in use, why. Advantages: Collect sand, grits, & floating objects. Disadvantages: 1. Produce mosquitoes. 2. Source of odors. 3. Must be cleaned frequently, this is costly. 4.This done by pumping the basin contents into trucks by means of a portable centrifugal pump. 5. Flushing Devices Formerly automatic flush tanks were used at upper ends of laterals where grades are low. Now they dont used. The flush is 750L of water. 6. Grease & Oil Traps Grease traps:They used after sewers from kitchens, hotels, garages & restaurants to trap grease which tends to accumulate on sewer walls & cause clogging.

Pipe Appurtenances

1 General Description This section includes the requirements for all pipe app Rubber gaskets Steel-bolted couplings Gate valves Sterilizing agents Bituminous plastic cement 1.01 Related References A. Standard Specifications Section 106Control of Materials Section 843Concrete Pipe2 Materials 2.01 Rubber Gaskets for Concrete Pipe A. Requirements 1. Type Use rubber-type gaskets and o-rings that meet the requirements of AASHTO M 198, Type A. However, pipe used in culvert construction does not need a hydrostatic pressure test. Ensure that pipe meets the applicable requirements of Section 843. If Section 843 and AASHTO M 198 differ, B. Fabrication General Provisions 101 through 150. C. Acceptance The Department will accept gaskets from approved QPL sources only. D. Materials Warranty A. Requirements 1. Coupling Types Use steel-bolted couplings for joining all types of plain end pipe. Ensure the couplings have the following characteristics: Wedge gasket and flared sleeve One steel middle ring, two steel followers, two wedge-shaped rubber-compounded gaskets, and steel bolts Dimensions and type for the size and kind of pipe to be joined, including reducers if required 2. Middle Rings a. Ensure that middle rings size 0.375 in (10 mm) through 3 in (80 mm) are fabricated from tubing and cold-formed to provide proper flare at each end and to receive the wedge portion of the gasket. b. Ensure that middle rings size 4 in (100 mm) and larger are made from either bar or plate-flash-welded, cold-formed, cold-expanded beyond the yield point of the steel to size the ring and proof-test the weld. c. Air-test all welded rings to ensure the weld is porous-free. d. Use middle rings that have a bellowed portion between the flares provided for the gaskets to accommodate pipe deflection. 3. Followers a. Ensure the followers meet these requirements: Size Fabrication 0.375 in (10 mm) through 1.5 in (40 mm) One piece steel forgings. Above 1.5 in (40 mm) through 5 in(130 mm) Cold-formed, two-piece construction. 5 in(140 mm) through 20 in (500 mm) Hot forged from a single piece circular plate & water quenched after forging for maximum strength. Above 20 in (500 mm) Use a special contoured mill section - circle-rolled, flash-welded and cold-expanded beyond the yield point of the steel to size the ring and proof-test the weld. All followers Have solid formed gasket recess, free of seams or breaks, to confine the gasket. 4. Gaskets Use gaskets that meet the requirements of ASTM D 2000 3AA708Z-B-13, with the following exceptions: Color Jet black Surface Nonblooming Shore A Durometer hardness 75 5 Tensile strength 800 psi (5.5 MPa ) minimum Elongation 175% minimum a. Use a rubber compound that will not deteriorate from age or exposure to air under normal storage or use conditions. Use natural or synthetic rubber that does not contain reclaimed rubber. Use gaskets that are immune to impurities such as odorants, liquid hydrocarbons, carbon dioxide, and water normally found in natural gas. To electrically bond the pipe ends to the center ring, make a permanent bond from material that cannot corrode or deteriorate and is molded into the tip of the gasket. 5. Bolts Use bolts that have elliptical necks and track heads. Align the elliptical neck and the elliptical hole in the follower so the bolt will not turn. a. Ensure that the shank of the bolts has enough threads to compress the gasket. Submit to the Engineer the manufacturers recommended torque for tightening the bolts. 6. Coating a. Unless otherwise specified, coat all metal parts in the shop to protect them during shipping and storage. After installation, apply a coat of coal-tar enamel to the coupling and uncoated ends of the pipe, according to 7. Certification Submit a certification from the pipe, gasket, or joint manufacturer to the Engineer, according to Subsection 106.05, Materials Certification. The certificate shall describe the physical properties of the rubber gasket and show the results on hydrostatic tests of the gasket and pipe used in the Work. B. Fabrication General Provisions 101 through 150. C. Acceptance The Department will accept the material based on the certification. D. Materials Warranty General Provisions 101 through 150. 2.03 Gate Valves A. Requirements Use gate valves that meet the requirements of AWWA C 500. B. Fabrication General Provisions 101 through 150. C. Acceptance The Department will accept the material based on the certification. D. Materials Warranty General Provisions 101 through 150. A. Requirements Use hypochlorites that meet the requirements of AWWA B 300 for sterilizing water systems. Section B. Fabrication General Provisions 101 through 150. C. Acceptance General Provisions 101 through 150. D. Materials Warranty General Provisions 101 through 150. 2.05 Bituminous Plastic Cement A. Requirements 1. Type Use a bituminous compound composed of steam-refined petroleum asphalt or refined coal tar that is dissolved in a suitable solvent and stiffened with a mineral filler with short mineral fibers. a. Ensure that the material is smooth and uniform, not thick, livered, or separating to a degree that it cannot be remixed by stirring. Ensure that the material can be applied with a trowel, putty knife, or caulking gun without pulling or drawing and has good adhesive and cohesive properties when applied to joint surfaces. You may apply the material cold to seal the joints of bell-and-spigot or tongue-and-groove storm or culvert pipe. Ensure that the bituminous plastic cement sets to a tough, plastic coating, without blistering when applied 1/16 to 1/8 in (2 to 3 mm) thick on a tinned metal panel and cured at room temperature for 24 hours. Use bituminous plastic cement with these characteristics: Minimum Maximum Grease cone penetration 175.00 250 Weight, lbs/gal (kg/L) 9.75 (1.2) Non-volatile, percent 75.00 Ash, by ignition, percent by weight 25.00 45

2. Use approved materials from those listed on QPL 21. B. Fabrication General Provisions 101 through 150. C. Acceptance Test as follows: Test Method D. Materials Warranty General Provisions 101 through 150. 2.06 Preformed Plastic Gaskets A. Requirements 1. Use cold-applied plastic gaskets that meet the requirements of AASHTO M 198, Type B to seal tongue-and-groove concrete culverts, precast manhole, and sewer pipes. However, do not perform the Flash Point COC and Fire Point COC tests. 2. Use approved materials from those listed in QPL 21. B. Fabrication General Provisions 101 through 150. C. Acceptance The Department will accept materials only from facilities listed in QPL 21 . D. Materials Warranty General Provisions 101 through 150.

Various Types of Pipes

The pipes are available in several types and sizes. They may be classified into three groups according to the material used in their manufacturing.

Metallic pipes: the pipes such as CI Pipes, Steel pipes and GI Pipes. Cement Pipes: the pipes such as Cement Pipes, Asbestos cement (AC) pipes, cement concrete pipes.Plastic Pipes: the pipes such as Un-plasticized PVC (UPVC ) pipes, Polythene Pipes (low denisity)

Cast Iron (CI) Pipes

These pipes are mostly used in water supply. They are well suited for pressure and can withstand external load because of their thickness. The pipes are easy in manufacturing, layout and joining. These pipes are manufactured by vertical casting in sand moulds, horizontal casting in sand moulds and centrifugal casting (spun casting pipes).Cast iron plumbing pipesCI Pipes - Strong and heavy.CI pipes are heavy in weight. Therefore transportation is costlier and they are not suitable for inaccessible places. Due to heavy weight these are generally made in short length. This increases layout and jointing cost. CI vertical casting pipes are not of very good quality and can be replaced by centrifugal casting (spun casting) pipes.

Steel PipesThese pipes are extensively used for water supply. They are best suitable for long distance pipe lines of high pressure and provide satisfactory performance during service. These pipes have excellent mechanical properties and are ideally suited for welding. The pipes are made in length more than twice the length of CI pipes; which saves in transport, layout of pipe and joining cost. There is minimum damage to the pipes in transportation. The pipes being light in weight are used for large diameter pipe lines.

Cement Pipes

Main advantage of cement pipes in place of metallic pipes is their corrosion resistance. These pipes are bulky, heavy and require careful transportation and handling. The layout process of these pipes is costlier than steel pipes. Asbestos Cement (AC) PipesThese pipes are light in weight and easy in transportation and layout. They have smooth internal surface and are not affected by corrosion (rust). The pipes are extensively used for water supply systems. Holes can be drilled in these pipes. These pipes are not costlier. Un-plasticized PVC (UPVC) Pipes

These pipes are rigid PVC pipes. They are light in weight, tough, resistant to chemical attack and large in length. Due to large in length the cost of handling is much whereas transportation and installation cost is less. Smooth internal surface of pipes provide less friction which results in saving of energy. These pipes are not suitable for the area which is very hot.

PVC plumbing pipes PVC plumbing pipes PVC plumbing pipes ,PVC Pipes - Light weight still powerfull.

RAINWATER HARVESTING Introduction A sufficient, clean drinking water supply is essential to life. Millions of people throughout the world still do not have access to this basic necessity. After decades of work by governments and organisations to bring potable water to the poorer people of the world, the situation is still dire. The reasons are many and varied but generally speaking, the poor of the world cannot afford the capital intensive and technically complex traditional water supply systems which are widely promoted by governments and agencies throughout the world. Rainwater harvesting (RWH) is an option that has been adopted in many areas of the world where conventional water supply systems have failed to meet peoples needs. It is a technique that has been used since antiquity.

Examples of RWH systems can be found in all the great civilisations throughout history. In industrialised needs of remote communities or individual households in arid regions. Traditionally, in Uganda and Sri Lanka, for example, rainwater is collected from trees, using banana leaves or stems as temporary gutters; up to 200 litres may be collected from a large tree in a single storm. Many individuals and groups countries, sophisticated RWH systems have been developed with the aim of reducing water bills or to meet the have taken the initiative and developed a wide variety of RWH systems throughout the world. It is worth distinguishing, between the various types of RWH practised throughout the world. RWH has come to mean the control or utilisation of rainwater close to the point rain reaches the earth. Its practice effectively divides into

Figure 1: Sigiriya, Sri Lanka. This reservoir cut into the rock was used centuries ago to hold harvested rainwater. Practical Action Domestic RWH RWH for agriculture, erosion control, flood control and aquifer replenishment. Rainwater harvesting Practical Action It is worth bearing in mind that rainwater harvesting is not the definitive answer to household water problems. There is a complex set of inter-related circumstances that have to be considered when choosing the appropriate water source. These include cost, climate, hydrology, social and political elements, as well as technology, all play a role in the eventual choice of water supply scheme that is adopted for a given situation. RWH is only one possible choice, but one that is often overlooked by planners, engineers and builders. The reason that RWH is rarely considered is often due to lack of information both technical and otherwise. In many areas where RWH has been introduced as part of a wider drinking water supply programme, it was at first unpopular, simply because little was known about the technology by the beneficiaries. In most of these cases, the technology has quickly gained popularity as the user realises the benefits of a clean, reliable water source at the home. the town supply is unreliable or where local water sources dry up for a part of the year, but is also In many cases RWH has been introduced as part of an integrated water supply system, where often used as the sole water source for a community or household. It is a technology that is flexible and adaptable to a very wide variety of conditions, being used in the richest and the poorest societies on our planet, and in the wettest and the driest regions of the world. Components of a domestic RWH system DRWH systems vary in complexity, some of the traditional Sri Lankan systems are no more that a pot situated under a piece of cloth or plastic sheet tied at its corners to four poles. The cloth captures the water and diverts it through a hole in its centre into the pot. Some of the sophisticated systems manufactured in Germany incorporate clever computer management systems, submersible pumps, and links into the grey water and mains domestic plumbing systems. Somewhere between these two extremes we find the typical DRWH system used in a developing country scenario. Such a system will usually comprise a collection surface (a clean roof or ground area), a storage tank, and guttering to transport the water from the roof to the storage tank. Other peripheral equipment is sometimes incorporated, for example: first flush systems to divert the dirty water which contains roof debris after prolonged dry periods; filtration equipment and settling chambers to remove debris and contaminants before water enters the storage tank or cistern; handpumps for water extraction; water level indicators, etc. Typical domestic RWH systems. Storage tanks and cisterns The water storage tank usually represents the biggest capital investment element of a domestic RWH system. It therefore usually requires careful design to provide optimal storage capacity while keeping the cost as low as possible. The catchment area is usually the existing rooftop or occasionally a cleaned area of ground, as seen in the courtyard collection systems in China, and guttering can often be obtained relatively cheaply, or can be manufactured locally. There are an almost unlimited number of options for storing water. Common vessels used for very small-scale water storage in developing countries include such examples as plastic bowls and buckets, jerrycans, clay or ceramic jars, cement jars, old oil drums, empty food containers, etc. For storing larger quantities of water the system will usually require a tank or a cistern. For the purpose of this document we will classify the tank as an above-ground storage vessel and the cistern as a below-ground storage vessel. These can vary in size from a cubic metre or so (1000 litres) up to hundreds of cubic metres for large projects, but typically up to a maximum of 20 or 30 cubic metres for a domestic system. The choice of system will depend on a number of technical and economic considerations listed below.

Figure 3: a) An owner built brick tank in Sri Lanka. b) A corrugated iron RWH tank in Uganda. Much work has been carried out to develop the ideal domestic RWH tank. The case studies later in this document show a variety of tanks that have been built in different parts of the world. 3 Rainwater harvesting Practical Action Collection surfaces For domestic rainwater harvesting the most common surface for collection is the roof of the dwelling. Many other surfaces can be, and are, used: courtyards, threshing areas, paved walking areas, plastic sheeting, trees, etc. In some cases, as in Gibraltar, large rock surfaces are used to collect water which is then stored in large tanks at the base of the rock slopes. Figure 4: A typical corrugated iron sheet roof showing guttering Practical Action Most dwellings, however, have a roof. The style, construction and material of the roof affect its suitability as a collection surface for water. Typical materials for roofing include corrugated iron sheet, asbestos sheet; tiles (a wide variety is found), slate, and thatch (from a variety of organic materials). Most are suitable for collection of roofwater, but only certain types of grasses e.g. coconut and anahaw palm (Gould and Nissen Peterson, 1999), thatched tightly, provide a surface adequate for high quality water collection. The rapid move towards the use of corrugated iron sheets in many developing countries favours the promotion of RWH (despite the other negative attributes of this material). Guttering Guttering is used to transport rainwater from the roof to the storage vessel. Guttering comes in a wide variety of shapes and forms, ranging from the factory made PVC type to home made guttering using bamboo or folded metal sheet. In fact, the lack of standards in guttering shape and size makes it difficult for designers to develop standard solutions to, say, filtration and first flush devices. Guttering is usually fixed to the building just below the roof and catches the water as it falls from the roof. Some of the common types of guttering and fixings are shown in figure 5. 4 Rainwater harvesting Practical Action Figure 5: a variety of guttering types showing possible fixings Manufacture of low-cost gutters Factory made gutters are usually expensive and beyond the reach of the poor of developing countries, if indeed available at all in the local marketplace. They are seldom used for very low-cost systems. The alternative is usually to manufacture gutters from materials that can be found cheaply in the locality. There are a number of techniques that have been developed to help meet this demand; one such technique is described below. V- shaped gutters from galvanised steel sheet can be made simply by cutting and folding flatgalvanised steel sheet. Such sheet is readily available in most market centres (otherwise corrugated iron sheet can be beaten flat) and can be worked with tools that are commonly found in a modestly equipped workshop. One simple technique is to clamp the cut sheet between two lengths of straight timber and then to fold the sheet along the edge of the wood. A strengthening edge can be added by folding the sheet through 90o and then completing the edge with a hammer on a hard flat surface. The better the grade of steel sheet that is used, the more durable and hard wearing the product. Fitting a downpipe to V-shaped guttering can be problematic and the V-shaped guttering will often be continued to the tank rather than changing to the customary circular pipe section downpipe. Methods for fixing are shown in figure 6. 5 Rainwater harvesting Practical Action First flush systems Debris, dirt, dust and droppings will collect on the roof of a building or other collection area. When the first rains arrive, this unwanted matter will be washed into the tank. This will cause contamination of the water and the quality will be reduced. Many RWH systems therefore incorporate a system for diverting this first flush water so that it does not enter the tank.

The simpler ideas are based on a manually operated arrangement whereby the inlet pipe is moved away from the tank inlet and then replaced again once the initial first flush has been diverted. This method has obvious drawbacks in that there has to be a person present who will remember to move the pipe. Other systems use tipping gutters to achieve the same purpose. The most common systuses a bucket which accepts the first flush and the weight of this water off-balances a tipping gutter which then diverts the water back into the tank. The bucket then empties slowly through a small-bore pipe and automatically resets. The process will repeat itself from time to time if the rain continues to fall, which can be a problem where water is really at a premium. In this case a tap can be fitted to the bucket and will be operated manually. The quantity of water that is flushed is dependent on the force required to lift the guttering. This can be adjusted to suit the needs of the user. 6 Rainwater harvesting Practical Action Another system that is used relies on a floating ball that forms a seal once sufficient water has been diverted . The seal is usually made as the ball rises into the apex of an inverted cone. The ball seals the top of the waste water chamber and the diverted water is slowly released, as with the bucket system above, through a small bore pipe. Again, alternative is to use a tap. In some systems (notably one factory manufactured system Although the more sophisticated methods provide a much more elegant means of rejecting the first flush water, practitioners often recommend that very simple, easily maintained systems be used, as these are more likely to be repaired if failure occurs. 7 Rainwater harvesting Practical Action Sizing the system Usually, the main calculation carried out by the designer when planning a domestic RWH system will be to size the water tank correctly to give adequate storage capacity. The storage requirement will be determined by a number of interrelated factors. They include: local rainfall data and weather patterns size of roof (or other) collection area runoff coefficient (this varies between 0.5 and 0.9 depending on roof material and slope) user numbers and consumption rates The style of rainwater harvesting i.e. whether the system will provide total or partial supply (see the next section) will also play a part in determining the system components and their size. There are a number of different methods used for sizing the tank. These methods vary in complexity and sophistication. Some are readily carried out by relatively inexperienced, first-time practitioners while others require computer software and trained engineers who understand how to use this software. The choice of method used to design system components will depend largely on the following factors: the size and sophistication of the system and its components the availability of the tools required for using a particular method (e.g. computers) the skill and education levels of the practitioner / designer Below we will outline 3 different methods for sizing RWH system components. Method 1 demand side approach A very simple method is to calculate the largest storage requirement based on the consumption rates and occupancy of the building. As a simple example we can use the following typical data: Consumption per capita per day, C = 20 litres Number of people per household, n = 6 Longest average dry period = 25 days Annual consumption = C x n = 120 litres Storage requirement, T = 120 x 25 = 3,000 litres This simple method assumes sufficient rainfall and catchment area, and is therefore only applicable in areas where this is the situation. It is a method for acquiring rough estimates of tank size. Method 2 supply side approach In low rainfall areas or areas where the rainfall is of uneven distribution, more care has to be taken to size the storage properly. During some months of the year, there may be an excess of water, while at other times there will be a deficit. If there is enough water throughout the year to meet the demand, then sufficient storage will be required to bridge the periods of scarcity. As storage is expensive, this should be done carefully to avoid unnecessary expense. This is a common scenario in many developing countries where monsoon or single wet season climates prevail. The example given here is a simple spreadsheet calculation for a site in North Western Tanzania. The rainfall statistics were gleaned from a nurse at the local hospital who had been keeping records for the previous 12 years. Average figures for the rainfall data were used to simplify the calculation, and no reliability calculation is done. This is a typical field approach to RWH storage sizing. The example is taken from a system built at a medical dispensary in the village of Ruganzu, Biharamulo District, Kagera, Tanzania in 1997. 8 Rainwater harvesting Practical Action Graph shows the comparison of water harvested and the amount that can be supplied to the dispensary using all the water which is harvested. It can be noted that there is a single rainy season. The first month that the rainfall on the roof meets the demand is October. I we therefore assume that the tank is empty at the end of September we can form a graph of cumulative harvested water and cumulative demand and from this we can calculate the maximum storage requirement for them dispensaryf

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