Check Valve Chatter in Closed Loop Ground Source Heat Pump

Old 10-16-17, 08:58 PM
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Unhappy Check Valve Chatter in Closed Loop Ground Source Heat Pump

I have two Ground Source Heat Pumps installed in our Ranch style home built on a slab. I have 5 -200 foot vertical loops. The main house has a 4 ton split system Water Furnace, that was installed in 2001 which works great. In 2009 I added a quest room w/ bathroom and added a 1.5 ton Water Furnace unit installed in the attic of the addition. Both systems run off the same 5 loops. Both systems still cool and heat the air just fine but the vibration noise from the small unit is unbearable in the guest room. The noise starts when the circulation pump in the attic comes on, not when the heat pump starts.

In the last few months the smaller unit developed a significant chattering noise. I called out the HVAC service company I have used for several years. Their diagnosis was the circulation pump needed replacing.for $900. I decided I could replace the motor cartridge myself for a lot less. When I replaced the cartridge I was careful to refill the system trying to remove all of the air i introduced from the loop. The old cartridge does not seem to have bad bearings but I have no way to test it positively. The small unit is in the attic and sits about 7 feet above the main unit so the install contractor installed an air vent valve on the discharge fitting of the heat exchange coil ahead of the circulation pump. I carefully reassemble everything but the chattering noise has persisted.

I called the service company back out and had them surcharge the loops. They raised the pressure on the loops to 40 psi, too much I thought but they assured me it would be fine. The chattering persisted.

The circulation pump is mounted so the flow is horizontal through the pump. I decided that there might be some air staying in the pump causing an off balance of the impeller. The old cartridge had a distinctive rust line across the impeller so I thought maybe the glycol fluid might not be filling the entire volute of the pump. The mounting of the pump had the the rotating axis of the pump off of horizontal by 5-10 degrees so I reconstructed the mounting so the axis is now 90 degrees from vertical as it should be, but the flow through the pump is still horizontal. It would be difficult to replumb the pump to run the vertically and the fluid still has to go down from the attic to the loops buried in the backyard. The circulation pump is pretty much at the top of the entire system, only a few inches below the discharge from the heat exchanger.

I think there might be air in the downstream side of the check valve. I was carefull reassembling the set up, I elevated the check valve and burped it while it still had back pressure on it. There are isolation valves on both sides of the pump so I was able to do all of the work on the pump with the system under some pressure, but I lost some of the 40 psi dropping it to 5 or 10 psi. After carefully reassembling and opening the isolation valves I let things sit overnight and then burped the air vent valve to assure all the air I could remove was gone. The chattering still persisted.

I purchased the needles and pressure gauge to inject water into the loops thinking maybe the pressure overcharge on the loops was too low after all of my work. I now have 20 psi at the ground level unit and 17 psi at the attic unit and those pressures are holding. The chattering still persists.

I am certain the problem is the check valve chattering. Using a screwdriver as a one ear stethoscope, the chatter is very loud at the check valve and diminishes towards the pump. The check valve is a Conbarco 125S, 400 WOG, ball cone spring loaded valve. The valve is mounted horizontally and is about 8 inches from the pump, a little close but it has been that way for over 10 years without any noise. The check valve is needed since there are 2 systems on the one set of loops, otherwise there would be short circuiting when one system was running and the other was not.

The only thing I can think to do next is to replace the check valve. I was thinking about doing the replacement with a spring loaded poppet style valve, for a softer close, with a side tap equipped with a needle valve on the downstream side for bleeding air. My thinking is that since the return line plunges down out of the attic from the check valve dissolved or free air is being pumped past the check valve, then migrating during non-circulations time back into the check valve. I don't understand why this would only start after 8 years of operation but then I am not a professional.
Any one have any thoughts, or answers?

Last edited by ROKJOK; 10-16-17 at 09:02 PM. Reason: Grammer
Old 10-17-17, 10:13 PM
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The higher water pressure would help get rid of air in the pipes but 17 should be okay. I would rather have 35 psi.

I have had homeowners complain of check valves that have acted this way for years when pipe insulation has come loose and allowed the vibration to be transmitted into a 2 x 4.

You want between 2 and 3 GPM of water Per Ton flowing through that Geothermal unit.
A spring actuated check valve may have an adverse effect on water flow.

Measuring GPM is not difficult if you have a Pete's plug immediately before and after the geo unit.
You only need the pressure drop across the unit, the temperature of the water entering the unit and the pressure drop chart found in the manual of that unit.

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