Question: What are the advantages and disadvantages of using gear pumps?    Answer: Gear pumps are a type of positive displacement pump that are appropriate for pumping relatively high pressures and low capacities. Advantages include the ability to handle a wide range of viscosities, less sensitivity to cavitation (than centrigual style pumps), relatively simple to maintain and rebuild. Disadvantges can include a limited array of materials of construction due to tight tolerances required, high shear placed on the liquid, and the fluid must be free of abrasives. Also note that gear pumps must be controlled via the motor speed. Throttling the discharge is not an acceptable means of control. Reference: The Pilot Plant Real Book, FXM Engineering, ISBN 0972176918

Question: How can I quickly estimate the horsepower of a pump?    Answer: Try this handy little equation: Horsepower = (GPM)(Delivered Pressure) / 1715 (Efficiency) GPM = Gallon per minute of flow Delivered pressure = Discharge minus suction pressure, psi Efficiency = Fractional pump efficiency

Question: How can I estimate the efficiency of a pump?    Answer: The following method, developed by M.W. Kellogg, gives results within 3.5% of most manufacturers curves.Eff % = 80-0.2855H+3.78x10-4 H F-2.23x10-7 H F2+5.39x10-4 H2 -6.39x10-7 H2 F+4.0x10-

10 H2 F2 H = Developed head, ft F = Flow in GPM (gallons per minute) Applicable for heads from 50 to 300 ft and flows from 100 to 1000 GPM

Question: What is the significance of the minimum flow required by a pump?    Answer: The minimum flow that a pump requires descibes the flow below which the pump will experience what is called "shutoff". At shutoff, most of the pump's horsepower or work is converted to heat that can vaporize the fluid and cause cavitation that will severely damage the pump. The minimum flow of a pump is particularily important in the design of boiler feed pumps where the fluid is near it's boiling point.

Question: How can I determine the largest impeller that a pump can handle?    Answer: The motor amperage should be measured in the field with the pump discharge valve wide open. Subtract about 10% from the pumps maximum rated amperage. Then the maximum impeller size can be determined from: A2 = A1(d2/d1)3 A2 = Maximum amperage minus 10% A1 = Current operating amperage d2 = Maximum impeller diameter d1 = Current impeller diameter

Question: How can one determine if a pipe is running full or is at its sealing flowrate?    Answer:

The following equation gives a quick check to determine the sealing velocity for a pipe: Q = 10.2 D 2.5 where Q is the liquid flowrate in gallons per minute D is the pipe diameter in inches If the current flowrate in the pipe is less than the value calculated for Q above, then the pipe is below its sealing flowrate or is said to be partially flooded. In order to calculate the velocity in this pipe you must use a set of flow area equation presented in Chemical Engineering magazine (March 1998, p. 129). The above equation is valid for liquid flow through a horizontal pipe.

Question: How can I determine the choked or sonic flow in an orifice?    Answer: Choked flow (also known as sonic flow) occurs when the ratio of the upstream gas pressure to the downstream gas pressure is equal to or greater than [(k + 1) / 2]k / ( k -

1) , where k is the specific heat ratio (Cp / Cv). For many gases, k ranges from about 1.1 to about 1.4, and so choked gas flow usually occurs when the upstream pressure is about twice the downstream pressure. The equation for choked flow is: Q = C A (g k d PU )1/2 [2 / (k + 1)](k +1) / (2k - 2) If the ratio of upstream to downstream gas pressure is less than [(k + 1) / 2]k / ( k - 1), then the flow is non-choked (i.e., sub-sonic) and the equation for non-choked flow is: Q = C A (2 g d PU)1/2 [k / (k - 1)]1/2 [(PD / PU)2/k - (PD / PU )(k + 1) / k ]1/2 where: Q = mass flow, lb/s C = discharge coefficient (usually about 0.72) A = orifice hole area, ft2 g = 32.17 ft/s2 gravitational acceleration k = Cp / Cv = (specific heat at constant pressure) / (specific heat at constant volume) d = gas density, lb/ft3, at upstream pressure PU = upstream pressure, lbs/ft2 PD = downstream pressure, lbs/ft2

Question: What are some good sources where I can find information about "real life" fluid dynamics and pumping systems?    Answer: 1) Flow of Fluids Through Valves, Fittings, and Pipe (Crane Technical Paper No. 410). Asking price = $10.00, but actually free. 2) Engineering Data Book; from the Hydraulic Institute. This one is definitely not free. It retails for $70, but should be available in your college library. 3) Pump Engineering Manual, 6th Edition. This is the old Durco Pump Manual which is now distributed by FlowServe. They ask for $10, but it is also free. 4) Goulds Pump Manual, GPM6. Look in section 7 - Technical Data. This is Free and you can also wrangle a free Goulds Pump selection computer program which describes all the performance data and curves of their entire line of pumps. Very useful. 5) Pumps and Systems magazine is free to qualified industrial pump users. Contact AES Marketing, Inc., 123 N. College Ave.; Suite 260; Fort Collins, CO 80524; ph (970) 221-2006 or Fax (970) 221-2019 for a free subscription. This magazine should be in your engineering library as well. Try their web site at WWW.pump-zone.com.

Question: For mixing with a circulation pump, what's a good rule of thumb to determine when the tank will be "well mixed"?    Answer: A common used rule is: time = (3* volume)/circulation rate for mixing with a circulation tan