How To Get Pump Piping Right
It's fairly easy to install a pump, but what about the piping? Getting your piping right the first time simply isn't as easy, which can cause your pump to fail prematurely. Rather than letting you wade through your manual, which only provides minimal information on pump piping arrangements, we've put together some tips on how to get your piping right.
1. Keep suction piping short and leak proof
Suction piping must be completely leak-tight and thus not allow any air pockets to form. For suction head installation, a slightly downward slope towards the pump is recommended, while a slight upward slope towards the pump is recommended for suction lift installation. Any sharp bends or changes in direction or cross-section are best avoided. It's also important keep suction piping short in order to ensure that inlet pressure drop stays as low as possible.
Note: Once suction piping reaches the horizontal run, it should slope upwards slightly, even on a flooded suction. This allows any vapor bubbles that might form to pass through the pump. If the suction horizontal run is long; a drain valve will need to located at the low point.
2. Ensure there is no strain on the pump
Any weight, stress or strains on your piping system can reduce pump performance. Make sure the pipes are supported near the pump, and bolts and connections on suction and nozzles are loose to ensure no stress is transmitted from the piping system to the pump.
3. Take note of connections
Pumps are fitted with connections, usually either on the pump casing to drain the pump or on the bearing bracket to evacuate seal leakage. You can also pipe drain and seal leakage to a nearby reservoir. Make sure that cooling, sealing and flushing of seal piping is connected to the designated connections located on the pump only.
4. Be sure of pipe sizing
Unfortunately, the nominal sizes of pump suction and discharge nozzles don't necessarily provide an adequate guide to the correct sizing of suction and discharge piping. Generally speaking, the nominal bores of the pipes should be the same as, or greater than, the pump nozzles. Pipes or accessories with a smaller bore should not be used.
High velocities can lead to high pressure drops, causing cavitation conditions in suction piping and excessive friction losses in discharge piping. According to many experts, the diameter of the pipe on the suction side should be equal to, or one size larger than, the pump inlet. This limits velocities to 7 or 8 feet per second or less.
5. Use straight run piping and isolating valves
By including 5 to 10 pipe diameters of straight run pipe between the pump inlet and elbow, you can negate or even eliminate "side loading" of pump impeller. This can also create more uniform pump axial bearing loading.
An isolating valve with valve stem in horizontal position should be included in positive suction head piping. This should be open during pump operation and never be used to regulate flow.
6. Regulate flow and head with a control valve
Install a control valve in the discharge pipe, as close to the pump as possible, to regulate required flow and head.
Should your pump need to operate at zero flow (against a closed discharge valve or near a closed valve with minimal flow), a minimum flow valve must be installed on the discharge nozzle or on the discharge piping.
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