We have a Sta-Rite Signature 2000 4” ¾ hp submersible water pump. The well is 227 feet deep; the water level is at 110 feet and the pump is down 147 feet. The pump is connected to an Amtrol Well-X-Trol bladder water tank. The Square D pressure switch is set to cut in at 40 PSI and cut out at 60 PSI. The tank pre-charge is 38 PSI.
I have verified that the above pressure settings are correct by following the procedure in the Signature 2000 owner’s manual available here: http://www.onga.com.au/secure/downloadfile.asp?fileid=1001397
TO CHECK PUMP PRESSURE SWITCH SETTING
- To check pressure switch setting, disconnect power to pump at supply panel (but be sure to leave pressure switch connected to power supply wires).
- Remove pressure switch cover.
- Open a faucet near tank.
- Allow water to drain until pressure switch contacts close; immediately close faucet.
- Check pressure at valve with standard tire gauge or with pump pressure gauge (if supplied).
- Pressure gauge should read at pump cut-in setting (30 PSI for 30-50 switch, 20 PSI for 20-40 switch, etc.) If not:
- Adjust switch according to switch manufacturer’s instructions.
- Reconnect power supply to pump and pump up pressure in system.
- Disconnect power supply to pump again and recheck switch setting.
- Repeat until pressure switch starts pump within ±1 PSI of proper setting.
- If cut-in setting is too low, system will rattle or develop water hammer when pump starts.
- Cut-out setting is not as critical as cut-in setting. Make sure that pump will stop running in a reasonable time. If it does not, cut-out setting may need to be adjusted down slightly. Be sure that after readjustment, system does not rattle or hammer on startup.
- Re-check tank air pre-charge to be sure it is 2 PSI below pump pressure switch cut-in setting.
When any upstairs faucet is drawing water and the pump starts, it starts with a bang (water hammer). On the other hand when I open the faucet located below the pressure gauge to draw down the water, the pump starts quietly when the cut-in setting is reached.
What is causing the water hammer at pump startup, and, more importantly, how do I get it to stop? Why would a low cut-in setting cause a water hammer?