1
1.
Path of the water
Figure 25: Suction pipe above the pump – incorrect
4.5.3 Suction-piping valve considerations
Suction valves
CAUTION:
Never throttle the flow from the suction side. Only use suction valves to isolate the pump for
maintenance, and install such valves in positions to avoid air pockets.
Before you install suction valves in the suction piping, review these considerations:
•
Make sure that the suction piping valves are placed right before the run of recommended straight
pipe.
•
Never throttle the pump with the use of a valve on the suction side of the pump.
•
Only use suction valves to isolate the pump for maintenance purposes.
•
Always install the valve in a position that avoids the formation of air pockets.
Foot valves
If the pump operates under static suction lift conditions, you can install a foot valve in the suction line in
order to avoid the necessity of priming each time you start the pump.
Before you install foot valves in the suction piping, review these considerations:
•
Make sure this valve is of the flapper type, rather than the multiple spring type, and that it is sized to
avoid excessive friction in the suction line.
•
Size the foot valve and pipe in order to maximize NPSH
A
to the pump by minimizing suction line
losses.
•
When foot valves are used, or where there are other possibilities of water hammer, close the dis-
charge valve slowly before you shut down the pump.
Check valves
In normal applications, check valves are placed in the discharge piping. Before you use a check valve in
the suction piping, consider the added pressure drop to the pump, the potential of water hammer, and
the chance of allowing the entire pump volute to be exposed to the discharge pressure.
Gate valves
Where two or more pumps are connected to the same suction line, install gate valves so that any pump
can be isolated from the line.
Before you install gate valves, review these considerations:
•
Always install gate valves on the suction side of the pumps with a positive pressure for mainte-
nance purposes.
•
Always install gate valves with the stems in a horizontal position to avoid air pockets.
•
Globe valves should not be used, particularly where NPSH is critical.
4.5 Piping checklists
Model 3410 Installation, Operation, and Maintenance Manual
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