Jet Pump Cavitation With CSV / Cistern

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Mr. Walker

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Well this is baffling, I just finished plumbing my new cistern tank to my jet pump (3/4hp AY Mcdonald Model 8670 with a shallow well/high pressure jet ejector using a 40/60 switch.) and then through my new AWESOME Cycle Stop Valve (csv1a) with a 4.4 gal pressure tank. After Adjusting the CSV to 50psi @ 2.5 GPM flow the jet pump starts cavitation pretty good until you back the pressure on the CSV back down to 40psi or less and it quiets down a lot. I've doubled checked for suction leaks and found non, so could I have a wrong jet size installed for a cistern feed setup or am I misadjusting the CSV with my set up?

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Valveman

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A pressure gauge somewhere between the pump and CSV would tell us a lot. 2.5 GPM flow is 2.5 GPM flow, it shouldn't matter if the pressure is set at 40 or 50. Now if you have the wrong jet and the pressure before the CSV maxes out at say 52 PSI, then you are just working too close to the max pressure this pump can build. A jet pump needs to be able to build a max pressure at least 10 PSI more than the off setting of the pressure switch. The pump would need to deliver a max pressure of 70 PSI to be able to use a 40/60 pressure switch.
 

Valveman

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You'd be better off skipping the csv and going to a conventional tank. You don't need a csv on a jet pump.

I agree you could fine tune a pressure switch to make a jet pump work like it has a CSV controlling it. But it is hard to set a pressure switch for a jet pump to not cycle at 1-2 GPM, and have any margin for error. The cut-off setting of the pressure switch must be very close to the max pressure the pump can build. If the water level drops a little, the pumps wears a tiny amount, or anything else causes the pump to not be able to reach that cut-off setting of the pressure switch, the water gets really hot and melts the pump. As with a pump that builds a max pressure of 62 PSI using a 40/60 switch. A little drop in water level or 1% wear in the pump and it will not be able to reach 60 PSI, which will melt it down in a few minutes, maybe an hour.

Either way you get strong constant pressure in the house and don't need a large pressure tank. But the CSV lets you operate well below the max pressure the pump can build, which gives a much larger window for adjustment. This makes it safer and easier to adjust. As with a pump that builds 73 PSI max using a 40/60 pressure switch. There is still plenty of room for a little wear in the pump or the water level to drop, as the pump would still be able to build to 60 PSI so the pressure switch can shut the pump off as it should. But there would need to be a CSV set at about 50 PSI to keep a system like this from cycling to death at low flow rates.
 

Mr. Walker

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Update; I installed a pressure gauge on the pump housing yesterday and it produces 75 PSI of water pressure while running. So, ether I somehow have a suction leak somewhere or the jet in the casing adapter is wrong/noisy. What would be the best way to check for suction leaks? Because I have two items on the suction line that possibly could cause a suction leak, one is a sch 80 pvc union between the pump and the ball valve. And the other is a rubber boot between the concrete cistern and the well house.
 

Valveman

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Those two things or anywhere else there is a thread could have a suction leak. You can foam the fittings with shaving cream and a hole will get sucked into the foam where the leak is. Or you can wrap one joint at a time with plastic wrap and see which one causes the cavitation noise to go away.
 
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