This is a list of centrifugal pump system tips or DOS AND DON’TS for pump systems. You may not of thought of some of these and they will help you design and trouble-shoot pump systems and select the proper pump. Also there is information here that is hard to find elsewhere. You can think of this list as GUIDELINES for the pump system designer.
1. Flow and pressure relationship of a pump
When the flow increases, the discharge pressure of the pump decreases, and when the flow decreases the discharge pressure increases
2. Do not let a pump run at zero flow
Do not let a centrifugal pump operate for long periods of time at zero flow. In residential systems, the pressure switch shuts the pump down when the pressure is high which means there is low or no flow.
3. Use pressure gauges
Make sure your pump has a pressure gauge on the discharge side close to the outlet of the pump this will help you diagnose pump system problems. It is also useful to have a pressure gauge on the suction side, the difference in pressure is proportional to the total head. The pressure gauge reading will have to be corrected for elevation since the reference plane for total head calculation is the suction flange of the pump.
4. Do not let a pump run dry, use a check valve
Most centrifugal pump cannot run dry, ensure that the pump is always full of liquid. In residential systems, to ensure that the pump stays full of the liquid use a check valve (also called a foot valve) at the water source end of the suction line. Certain types of centrifugal pumps do not require a check valve as they can generate suction at the pump inlet to lift the fluid into the pump. These pumps are called jet pumps and are fabricated by many manufacturers.
5. Suction valves
Gate valves at the pump suction and discharge should be used as these offer no resistance to flow and can provide a tight shut-off. Butterfly valves are often used but they do provide some resistance and their presence in the flow stream can potentially be a source of hang-ups which would be critical at the suction. They do close faster than gate valves but are not as leak proof.
6. Eccentric reducer
Always use an eccentric reducer at the pump suction when a pipe size transition is required. Put the flat on top when the fluid is coming from below or straight (see next Figure) and the flat on the bottom when the fluid is coming from the top. This will avoid an air pocket at the pump suction and allow air to be evacuated.
7. Use a multi-stage turbine pump for deep wells
For deep wells (200-300 feet) a submersible multi-stage pump is required. They come in different sizes (4″ and 6″) and fit inside your bore hole pipe.
8. Flow control
If you need to control the flow, use a valve on the discharge side of the centrifugal pump, never use a valve on the suction side for this purpose.
9. Plan ahead for flow meters
For new systems that do not have a flow meter, install flanges that are designed for an orifice plate in a straight part of the pipe (see next Figure) and do not install the orifice plate. In the future, whoever trouble-shoots the pump will have a way to measure flow without the owner having to incur major downtime or expense. Note: orifice plates are not suitable for slurries.
10. Avoid pockets and high points
Avoid pockets or high point where air can accumulate in the discharge piping. An ideal pipe run is one where the piping gradually slopes up from the pump to the outlet. This will ensure that any air in the discharge side of the pump can be evacuated to the outlet.
