7
D10-991-2400 5/1/04
D/G-10 Installation
Discharge Piping
Hose and Routing
Use the shortest, most-direct route for the discharge line.
Select pipe or hose with a working pressure rating of at least
1.5 times the maximum system pressure. EXAMPLE: Select a
1500-psi W.P.-rated hose for systems to be operated at 1000-
psi-gauge pressure.
Use about 6 ft (1.8 m) of flexible hose between the pump and
rigid piping to absorb vibration, expansion or contraction.
Support the pump and piping independently. Size the discharge
line so that the velocity of the fluid will not exceed 7-10 ft/sec
(2-3 m/sec):
For pipe in inches: Velocity (ft/sec) = 0.408 x GPM/Pipe ID
2
For pipe in mm: Velocity (m/sec) = 21.2 x LPM/Pipe ID
2
NOTE: Pumps with non-metallic pumping head are
limited to 250 psi (17 bar) maximum working pressure
rating.
Pressure Regulation
Install a pressure regulator or unloader in the discharge
line. Bypass pressure must not exceed the pressure limit of
the pump.
Size the regulator so that, when fully open, it will be large enough
to relieve the full capacity of the pump without overpressurizing
the system.
Locate the valve as close to the pump as possible and ahead
of any other valves.
Adjust the pressure regulating valve to no more than 10% over
the maximum working pressure of the system. Do not exceed
the manufacturer’s pressure rating for the pump or regulator.
Route the bypass line to the supply tank, or to the suction line
as far as possible from the pump (to reduce the chance of
turbulence and cavitation).
If the pump may be run for a long time with the discharge closed
and fluid bypassing, install a thermal protector in the bypass
line (to prevent severe temperature buildup in the bypassed
fluid).
CAUTION:
Never install shutoff valves in the bypass line
or between the pump and pressure regulator.
Provide for permanent or temporary installation of a pressure
gauge to monitor the discharge pressure at the pump.
For additional system protection, install a safety relief valve in
the discharge line, downstream from the pressure regulator.
Net Positive Suction Head
NPSHa must be equal to or greater than NPSHr. If not, the
pressure in the pump inlet will be lower than the vapor pressure
of the fluid — and cavitation will occur.
Calculating the NPSHa
Use the following formula to calculate the NPSHa:
NPSHa = Pt + Hz - Hf - Ha - Pvp
where:
Pt = Atmospheric pressure
Hz = Vertical distance from surface liquid to pump centerline (if
liquid is below pump centerline, the Hz is negative)
Hf = Friction losses in suction piping
Ha = Acceleration head at pump suction
Pvp = Absolute vapor pressure of liquid at pumping temperature
NOTES:
•
In good practice, NPSHa should be 2 ft greater than NPSHr
•
All values must be expressed in feet of liquid
Atmospheric Pressure at Various Altitudes
Altitude
Pressure
Altitude
Pressure
(ft)
(ft of H
2
O)
(ft)
(ft of H
2
O)
0
33.9
1500
32.1
500
33.3
2000
31.5
1000
32.8
5000
28.2
