MIL-HDBK-1005/16
provided to allow operation over the entire flow range (minimum
flow with new stators and rotors; maximum flow with worn stators
and rotors). Determine the motor horsepower based on worst-case
hydraulics, not including the added 50 percent capacity
allowance. Also, the minimum horsepower necessary to start the
pump must be provided. Proper selection of the pump speed range
is essential. The average operating speed should be in the range
of 40 to 80 rpm and should never exceed 200 rpm.
10.4.3
Plunger Pumps. A plunger pump, also called a piston
pump, is a positive displacement pump in which a reciprocating
piston displaces its volume on each stroke. This pump has the
capability to self-prime to low suction lifts of up to 10 feet
(3 m), although it is recommended that these pumps be used under
flooded suction conditions to avoid priming problems. Suction
and discharge ball check valves are provided to prevent backflow
during operation. To reduce surge in lines, air chambers should
be provided on all discharge pipes and on suction pipes with more
than 5 feet (1.5 m) of suction head.
One disadvantage of plunger pumps is their frequently
messy operation. Oil must be added every shift, and it usually
leaks around the pump area. Packing glands on the plunger
usually leak, so it is recommended that an easy means of
containing the spills and cleaning the pump area be included in
the system design.
10.4.3.1 Pulse Flow/Capacity Considerations. Plunger pumps are
relatively limited in capacity (75 to 250 gpm [4.7 to 16 L/s]).
The discharge is varied by manually adjusting the stroke length.
Stroke frequency is usually controlled by a timer. The system
must be designed for the pump's pulse flow, not its rated
capacity, as listed below:
Type of Pump
Pulse Flow/Rated Capacity
Simplex
3.10
Duplex or two simplex
1.55
Triplex or three simplex
1.20
Two duplex
1.10
As indicated, duplex and triplex pumps give a smoother
flow than simplex pumps, which reduces horsepower requirements.
Because of their pulsating flow, direct flow measurement can be
difficult. Analog devices that produce a signal proportional to
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