maintenance & cost reduction in a wastewater facility webinar

2016 Wastewater Webinar Series – Part 1Paul Keough

Shaft Sealing and Water Reduction Strategies in Water & Wastewater Treatment

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The World of Chesterton

• Founded 1884• Headquartered in

Woburn, Massachusetts, US

• Global Manufacturing• Worldwide distribution

and service centers• Revenues of $235 million• 1200 people

North America160 Sales and

Service Locations

South America42 Sales and

Service Locations

Europe, Middle East & Africa234 Sales and

Service Locations

Asia Pacific66 Sales and

Service Locations

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Who we are…• A leading global manufacturer of

industrial fluid sealing systems, advanced polymer composites, cleaners, lubricants, metalworking fluids and industrial specialty products

• A company with a strong commitment to innovation, helping our customers with products and programs that help them operate more reliably, efficiently and economically

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Focus for TodaySealing Strategies …think about the following:

Seals represent 2 – 5% in the overall acquisition cost of a pump.

70 – 80 % of unscheduled pump shutdowns are seal/packing related.

So it’s critical to understand what sealing system is needed and how you ask for it.The art is SPECIFYING the best sealing system…without

overkill!ENHANCE operation & MAXIMIZE Value

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Common Sealing StrategiesStrategies

Mechanical Packing Single Component Seals Cartridge Seals Split Seals Zero/Reduced Flush Sealing System

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Common Sealing Strategies

Mechanical Packing

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Mechanical Packing• Resilient material formed

around the shaft to create a long axial seal

• An adjustable gland is used to compress the packing between the stuffing box bore and the shaft

• Tightening the gland reduces the clearance

• As the shaft rotates, it wears additional clearance into the packing.

• This necessitates further gland tightening

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Mechanical Packing

Friction between the shaft and packing generates heat and wear leading to swift deterioration of the shaft/sleeve.

Also solids or abrasives in the pumped fluid imbed into the packing and wear at the shaft/sleeve

Flush water must be introduced via a lantern ring to lubricate the packing arrangement.

This flush must leak to the environment.

FLUSH WATER

FLUSH WATER

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Excessive Wear on Shaft Sleeves

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Excessive Wear on Shaft Sleeves

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Advantages

• Inexpensive acquisition cost• Don’t have to dismantle the pump

PerceptionsEasy to install• Easy to replace packing

Packing Summary

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Disadvantages

• Designed to leak.• Requires excessive flush water for

lubrication and cooling.• Shaft/sleeve damage and replacement• Requires frequent adjustment.• Housekeeping costs from leakage.• Leakage impact: bearing failure; corrosion• Added power consumption

• (like driving your car with the brake on)

Packing Summary

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Common Sealing Strategies

Mechanical Seals

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Mechanical Seals

• Consists of two extremely flat surfaces, called faces

• Held together by product pressure and spring force to prevent product from escaping to the environment.

• Visible leakage that comes from compression packing is usually eliminated

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Mechanical Seals

• All seals have common basic elements• Primary seal (rotary and stationary faces)• Spring mechanism (single spring, multi-spring, bellows) • Secondary Seals (o-ring, bellows, v-rings)• Metal components

• In Water and Wastewater:• Component Seals• Single Cartridge seals• Split Seals

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Component Seals

• Most of your low cost seals typically are component seals

• Can vary somewhat in cost and widely in performance.

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Component Seals

• Consists of the four key components of a seal: Primary seal (Faces), Secondary Seal (Teflon Wedge), spring element and metal parts).

• All these elements are installed at the pump manufacturer or at the end user site.

• Requires precise measurements for proper installation.

Primary sealPrimary seal

Stationary Stationary faceface

Rotating faceRotating face

Secondary sealSecondary seal

SpringsSprings

O

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Component Seals

• Seal faces must remain clean and undamaged during handling and installation.

• Incorrect installation can occur resulting in premature seal failure

• The majority of seal failures for component seals come from mis-installation or mis-application.

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Cartridge Seals

Advantages:•Self contained assembly of all components•No special skills required for installation•Hydraulically balanced•Will not fret or damage shaft

Disadvantages:• Initial Acquisition Cost higher than

Component Seal• Must disassemble pump to remove the

seal

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Cartridge Seals

Disadvantages:• Initial Acquisition Cost higher than Component Seal• Must disassemble pump to remove the seal

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Cartridge Seals – Desired Features

• Stationary seal: Stationary face shall be spring loaded to provide self-alignment due to stuffing box misalignment

• Spring should be Hast C and located outside of the pumped fluid

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Common Sealing Strategies

Split Mechanical Seals

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Split Seals

• No Equipment Disassembly• On large pumps, multiple trades

required to remove/install component or cartridge seals (electrician, pipe fitter, rigger, mechanic)

• No Coupling Re-Alignment• Easiest Field Reparability• Safety

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Split Seal Advantages

MOST PRACTICAL SEAL TO INSTALL ON LARGE SHAFT DIAMETERS (Greater than 2.5”) (Multiple trades issue)

When it is too difficult to change the packing sleeve or non-split seal

When down-time is expensive or critical/unacceptable Comparable in cost to cartridge seal Spare parts kits are relatively inexpensive No re-alignment of pumps required Newest designs very easy to install.

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Split Seal Features

Both pressure and vacuum capability

Secondary seal will not damage shaft or sleeve

Springs out of the process fluid Hydraulically balanced seal Minimal number of components Field repairable

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Mechanical Seal Selection Criteria

Common Sealing Strategies

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Seal Selection Criteria

• Fluid Properties• Operating Conditions• Equipment to be sealed

• Seal Design Chosen• Material Compatibility / Suitability• Environmental Controls Selected

Solids? Temp?

Pressure? Speed?

Shaft size?

Cartridge or Split?

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Selection Considerations: Split Seal vs. Cartridge Seal

• Shaft Size < 2.50”: Cartridge Seal• Easiest seal type to install• Due to relatively small pump

size, pump dismantling not overly difficult or time consuming.

• Shaft Size > 2.50”: Split Seal• Pump removal/dismantle

required – not easy to repair on site.

Cartridge Split

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Materials of Construction

• Water with varying degrees of Solid / Abrasives:• Face materials: HARD FACES

= Silicon Carbide vs. Silicon Carbide

• Secondary Seals: FKM, EPR or Aflas*

• Springs: Hastelloy C** or Elgiloy***

• Misc. Metal Parts 316 SS

* Registered TM of Asahii Glass Co. **Registered TM of Hayes Int’l *** Registered TM of Elgiloy Ltd. Partnership

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Environmental Controls for Seals

Common Sealing Strategies

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Environmental Controls

Strategies utilized to control the temperature, pressure and the fluid inside the stuffing box.

The controls ARE the life support system for the seal.

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Environmental Controls

From a major pump manufacturer…

“SEAL ENVIRONMENT IS CRITICAL FOR EXTENDED SEAL LIFE.The #1 cause of pump downtime is failure of the shaft seal. These failures are normally the result of an unfavorable seal environment such as improper heat dissipation(cooling) and poor lubrication of the seal faces or seals operating in liquids containing solids, air or vapors.”

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Environmental Controls

• In Water & Wastewater Treatment, controlling fluid properties and removing trapped air are the most significant concerns

• Preventing solids buildup, keeping abrasives from seal faces, & preventing heat generation at the seal faces

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Environmental Controls

• Most common single seal control: FLUSH• Clean, cool fluid with restrictor bushing in the stuffing

box throat to create flow• Strategy:

• Try to prevent solids build up in stuffing box (15 fps under bushing)• Try to keep abrasives away from faces, • Try to push air out of stuffing box and force liquid film lubrication

across seal faces.

• Source of Flush water:• City Water• Plant Effluent

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API Plan 32 – Clean Flush

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Issues with Flush Water to Seals

Capital cost of flush systems Reliability of flush water systems

Loss of system causes seal failure Quality of Flush???? No Worries on quality…

We use City Water We use Plant Effluent

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Issues with Flush Water to Seals

• City Water: Typical Cost of flush: $.002/ Gal .• Pump shaft size: 2.000”• Typical Flush rate: 2 GPM

per pump • $.002 x 2GPM x 60 Min x 24

Hrs. x 365 = $2102.72

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Issues with Flush Water to Seals

Plant Effluent: Cost of retreating water that has been through the plant = $$$$

Vertical Pump

(Flooding)

• AbrasivesEnter seal cavity

as pump is flooded.

• AirTrapped around seal face must be

vented off

BACK TO SUCTION1/8”(3.18mm) ORFICE

Vertical Applications –

API Plan 13

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“State of the Art” Sealing• Seal Design to Minimize Life

Cycle Cost• Split seals

• Effective Environmental Control• Active Throat Bushings

• Reduce or Eliminate Flush Water Requirement

• Eliminate flush water system wherever possible

• Improve Pump/Seal Reliability• Reduce Plant Operating Cost • Satisfies KISS Principle: reliance

on flush water can add unnecessary complexity

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Active Throat Bushing

Active Throat Bushing is used with Split Mechanical Seals

to reduce or eliminate flush fluid required and

further enhance seal reliability by driving

seal cavity circulation and exchange

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Zero / Reduced Flush Technology

Split Seal

Active Throat Bushing

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Trapped Air in Stuffing BoxTrapped Air in Stuffing Box

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Air Migrates to Seal FacesAir Migrates to Seal Faces

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Air Removed by Active Throat Air Removed by Active Throat BushingBushing

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Dirty Process Fluid in Stuffing BoxDirty Process Fluid in Stuffing Box

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Active Throat Bushing Extracts SolidsActive Throat Bushing Extracts Solids

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Active Throat Bushing TechnologyActive Throat Bushing Technology

From one municipal client…

“…active throat bushings are both an economically and environmentally responsible upgrade for your pumping applications.”

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Common sealing strategies:- Packing & Mechanical Seals: - Design features- Advantages & disadvantages

Seal Selection & Criteria in Water & Wastewater Environmental Controls State of the Art Sealing in Water & Wastewater

- Split Seals & Active Bushing Technology

SummarySummary