Pump switch problem

Old 03-01-10, 03:10 PM
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Pump switch problem

I have a open loop geothermal system. Water comes in from a 50' well and dumps into the lake. I have had a nasty knocking sound from the pipes when the water valve is triggered from the thermostat that it has reached its temperature. I have replaced the 36 gallon pressure tank which is at 27.5 PSI. Replaced the water sprinkler valve at the unit, and replace the pressure switch (30-50 psi)I also had the water well pump and the wiring replaced and then tested. I do not have a checkvalve installed (after reading some of the other forums this was mentioned and I do not know where to install if needed) The tank is approx 30' from the pressure switch also. I set the switch to start up at 29.5psi. However the only way I could get the knocking to stop (lasted usually 2-3 minutes) was to increase the pressure switch to 47psi startup. There is still a loud knock but only for a second or two. Help!!
Old 03-02-10, 04:16 PM
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Why isn't the pressure switch by the tank? With it located so far from the tank, you might be suffering from that infamous pressure wave syndrome we have been discussing here a little bit lately. That could be the cause of the multi-second banging you get.

Also, early on in your post, you say that there is this knocking that occurs after set temp is reach, and a water valve is activated. Could it be that this valve is shutting off the geothermal pump water, and is causing water hammer? If so, a water hammer arrestor should be your cure.

But what I don't understand is if a pro installed this system, you'd think they would know this, and would have installed one as standard procedure. Unless they DID install one, and the air escaped either because they used a bladderless type, or something happened to the bladder style one, if you have one in-line, that is. And then also - if a pro installed the system, what made them install the pressure switch so far away from the tank?
Old 03-02-10, 06:54 PM
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The pressure switch should be mounted no more than 3 feet from the tank, on the inlet side. The valve that opens and closes the flow to your system, should be on the out going side of the tank, or down stream for the tank.

It kinda sounds like the psi in the tank and the setting of the pressure switch are just not set correctly.

The thermostat you are using, is it the mercury type?
If it is, change it!
As they get older the spring inside gets weak, and WILL cause the switch to bounce.

It would be easier, and more accurate to set the pressure in the tank to the on psi of the switch, and not try to set the switch. Most pressure switches are not that sensitive, and are very hard to get a setting that close.The tank is a much better way to get these settings correct.
The tank should be 3psi less than the ON setting of the pressure switch.

There should be a check valve in the pump, and that would be the only one you need with a bladder tank.
The only time more than one is needed, is with a pneumatic tank, or one with no bladder.

Did the system have this bounce, hammering or banging of the pipes before you had the components changed?
If it did not, What part that was changed, is not back in the place it came from, or is maybe a differnt size part, than that was there before the change?

Old 03-04-10, 04:39 PM
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I had knocking when the pump started from my well, it was the bottom checkvalve at the pump leaking down.

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