Pump Selector Calculation

Contents of this page:

Minor Loss Coefficient Calculator. Enter the
number of elbows, valves, fittings, etc. that exist on the suction and discharge
pipelines. The calculation computes the sum of the minor loss coefficients for each
pipeline. These sums (K_{s} and K_{d}) are then entered into the
second calculation.

Pump Selector Calculator. Computes Total
Dynamic Head (TDH) and Net Positive Suction Head Available (NPSH_{A}) for a piping
system, then determines which pumps in the Master Pumps database satisfy the pump type,
capacity, TDH, temperature, and NPSH requirements for the system.

Discussion Piping Scenarios Equations Variables Error Messages References

Minor Loss Coefficient Calculator

Enter the number of fittings of each type on the suction and discharge sides of the
pump. The sum of the minor loss coefficients is computed and entered manually in Pump Selector Calculation that follows. Minor
loss coefficients were obtained from Mays (1999).

Discussion
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The pump selector calculation lists up to nine
pumps from the database that match the following criteria. To be listed, a pump
must:

· Be the type of pump that the user selects.

· Must have a maximum capacity greater than the system requirement and less than 1.25
times the system requirement.

· Must be able to supply a maximum TDH greater than the system requirement but less than
1.25 times the system requirement.

· Must have an NPSH requirement less than the NPSH available.

· Must have a maximum temperature rating higher than that of the liquid being pumped.

Pumps are sorted in order of increasing price.

Piping Scenarios
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Terminology:

"Main" can physically represent several different things: It could be a
water main or any large diameter pipeline having a smaller diameter pipe (a lateral) that
branches off of it. It could also be a tank that is under pressure.

"Reservoir" is a tank or lake whose surface is open to the atmosphere.
The calculation automatically sets a reservoir's pressure (P_{1} or P_{3})
to 0. Note that a reservoir is a main with a pressure of 0.

In all scenarios, flow is from 1 to 3. It is okay if Z_{2}-Z_{1}
and/or Z_{3}-Z_{2} is negative.

Equations
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The following equations are the standard equations for flow of viscous fluids. They
can be found in many fluid mechanics textbooks, some of which are listed in references. The Darcy-Weisbach friction loss method is used
because it allows major losses (pipe friction) to be determined for any fluid.

Horsepower and Affinity Laws (0.7 is efficiency, D is impeller diameter):

Variables
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[] indicates units: [L] means variable has units of length, [F] force, [M] mass, [P]
pressure, [T] time, [t] temperature.

Heads are typically expressed in length units, such as ft. However, they can be
expressed in pressure units such as psi (by multiplying the head by the weight density, *W*,
of the fluid). Likewise, pressures can be expressed in units of head (by dividing by
the fluid's weight density).

Subscripts:

*1* indicates location 1. *2* indicates location 2 (pump inlet).
*3* indicates location 3.

*s* indicates the suction pipeline (pipe and fittings between locations 1 and 2).

*d* indicates the discharge pipeline (pipe and fittings between locations 2 and 3).

*A _{s}* = Cross-sectional area of suction pipeline [L

NPSH = Net positive suction head [L]. The calculation computes NPSH

TDH = Total dynamic head [L].

Error Messages To top of page

>From Minor Loss Calculator:

From Pump Selector Calculation:

*"e, L's, K's must be >= 0."* Pipe roughness, and suction and
discharge pipe lengths and minor losses cannot be negative. Check your input.
These must be >= 0.

*"Q, S, y, P*_{v}*, Patm, D's must be > 0."*
Flowrate, specific gravity, dynamic viscosity, vapor pressure, atmospheric pressure, and
suction and discharge pipeline diameters must be positive. Check your input.
At least one of these was entered as <= 0.

*"T must be > 0K."* Temperature was entered as below absolute
zero. Check your input.

*"TDH <= 0. Pump not needed."* Total dynamic head was
computed to be <= 0. This means that a pump is not needed; therefore, no pumps
are listed.

*"Pump 32 has 8 commas."* This is a check of the pump data entered.
There must be 10 commas in each pump record. This message indicates that the
32nd pump typed in has 8 commas in its record. This is an example; it could be any
pump and any number of commas other than 10. Check the input field corresponding to
the pump number indicated.

*"Database error - Pump #19's type (Booster/Injector) is invalid."*
Pump types listed in the database must match a pump type in the Java computer
program. Booster/Injector is not a pump type in the program - Booster is. If
you have an injector pump, call it a booster pump. This is an example; it could be
any pump number in the database and any type that doesn't match. Check the pump
drop-down menus to see the allowable pump types.

*"Re or e/D out of range."* Reynolds number or roughness to
diameter ratio is out of range for the suction or discharge pipeline. *Re*
and *e/D* must be in the proper ranges (shown above in equations)
in order for the friction factor to be computed. Check your input to make sure the
units are what you intended and that your numbers are correctly entered.

References
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Mays, L. W. editor. Hydraulic Design Handbook. McGraw-Hill, Inc. 1999. (Minor loss coefficients were obtained from p. 22.7)

Munson, B.R., D. F. Young, and T. H. Okiishi. 1998. Fundamentals of Fluid Mechanics. John Wiley and Sons, Inc. 3ed.

Streeter, V. L., E. B. Wylie, and K. W. Bedford. 1998. Fluid Mechanics. McGraw-Hill, Inc. 8ed.

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