I have had an open loop system since 2007 which has worked well without any major problems for a the last 9 years. The only real repair I have had to do is the replacement of the pressure switch for the pressure tank (which is a solenoid type switch). The pressure switch was replaced around 4 years ago. Yesterday, I hear a really loud thudding noise when the pressure switch cuts off at the end of the cycle. I assume this is a sign that the pressure witch is going to fail again. Am I correct? Since this is the second time the pressure switch appears to be giving way, I was curious if there is a good/better solution than the standard pressure switch? I hear people in this forum discuss the use of a variable speed pump or Cycle Stop Valves. Would the experts here recommend either of these? Are there operating cost benefits to using any of these? Any advice is appreciated. Thanks in advance.

Sounds like water hammer - if true, this can be solved with a water hammer arrestor located near a closing valve (eg the HP).

A dual pressure system (high pressure for domestic water, low for the heat pump) will be more energy efficient.

Thanks for the response. I don't use the well for any domestic water - only for the heat pump for heating and cooling. It sounds like a water hammer. Is there any reason why it suddenly shows up. I also noticed that the pressure gauge which is usually set to between 22-40 now appears to go to 45 on the upside and when it hits 20 on the downside, it suddenly drops to 10 before it goes back to 20. Is that because of the water hammer or is something else likely wrong with the pressure tank? I will get a well person to take a look at it tomorrow. Thanks!

Have him look at lowering the pressure to as low as it can go while maintaining your required GPM through the HP (perhaps 10 psi). Then adjust the upper limit so that the pump doesn't cycle too often (> 2 min?). Also verify that the pressure tank is working and charged properly for the low pressures that you want to use.

I'd look into getting a pump so that is sized such that it pumps the right GPM/PSI continuously while the HP is on (ie, never over-pressurizes or cycles). But look at other solutions if the water level in your well changes significantly.

As long as you have a single stage heat pump, you can match the output of the well pump to the demand of the heat pump and the well pump will not cycle on and off. But if you have 2 or more stages to the heat pump, the flow rate will vary and you will need a Cycle Stop Valve or something to vary the flow from the well pump to prevent cycling.

Since you are having problems with the pressure switch, I would guess that your well pump cycles on and off while the heat pump is running. Cycling is not good and will shorten the life of the well pump. I hear from lots of heat pump owners who say it doesn't matter how much energy the heat pump saves if they have to buy a new well pump every 18 months to 3 years from being cycled to death.

Not only does cycling shorten the life of the pump, but it also shortens the life of the pressure switch, bladder in the tank, and the check valve. Your check valve has slammed shut so many times from the pump cycling that it is failing. The check valve is sticking open, the spring is weak, and the water has to reverse direction to shut the check valve. This is what is causing the water hammer when the pump shuts off.

Not only does a Cycle Stop Valve eliminate cycling and make the pump last longer, but it also makes the bladder tank, pressure switch, and even the check valve last longer. Not only does it greatly reduce the number of cycles, but the Cycle Stop Valve actually reduces the flow to 1 GPM before the pump does shut off. This means the check valve is only open the thickness of a piece of paper when the pump shuts off, which eliminates the slamming and water hammer. Along with the reduction of of cycles, a mechanical soft start and soft stop from the Cycle Stop Valve greatly increases the life of the check valve.

The change in sound when your pressure switch is cutting off is most likely caused by a failed bladder or incorrect precharge in your pressure tank. When working correctly the tank should be abled to absorb the shock of the pump turning abruptly off. If you still suspect it is the pressure switch usually the first sign of failure is on/off pressures drifting beyond original settings. Variable speed pumps work great with geothermal but come at a cost. Only you can decide whether it is worth the investment for increased efficiency.

As valveman said, it sounds like a check valve to me. Whether it is in the pump or in your house or both. Just curious; but how deep is your well?

Where does the water go out of the heatpump?

Sorry I have been on the road and haven't had an opportunity to check on the responses. Thanks for all your responses. I will try and address the questions raised. It might be a check valve since it makes the sound when cutting in at around 20 psi when the pressure switch is acting. There is no sound when it hits the higher pressure around 40 psi. The well is about 250 feet deep. The water is sent back to the well - it is not used. I can ask the well service guys to see if they know about cycle stop valves. And also ask for how much it would take to go with a variable speed pump. Someone told me that there are also different pump controllers that one can use instead of the pressure switch. Is that correct? Or is a pump controller only used with a variable speed pump? Can someone enlighten me on this? Thanks for all your insights in advance!

Water hammer on pump start is caused by having more than 1 check valve in the line. Pressure switch failure is one of the first signs you are cycling the pump on/off too much. And this cycling is also what causes check valves to wear out among other things. When the lower check in the system leaks back a tiny amount or just begins to close slower than the upper check, the upper check is holding the water in the drop pipe, the same as holding your finger over a straw full of ice tea. This leaves the water in the drop pipe hanging at a negative pressure. So when the pump starts it re-pressurizes the water in the drop pipe almost instantly. The water below the upper check will fly up and hit the upper check just like a boxer punching you in the nose as hard as he can. This is what causes the water hammer on pump start.

You can just remove the upper or above ground check valve and this problem will go away. If the lower check is still good, the additional pressure from removing the upper check will hold the lower check closed better. If the lower check continues to leak back, it will need to be replaced no matter what.

You really need to address the cycling problem as wearing out pressure switches and check valves is just the first sign that you are going to need a new pump soon. There are only a few ways to control a pump like that. The pressure switch is the most common and the most reliable, especially when used with a Cycle Stop Valve to stop the cycling. A variable speed pump or VFD will require a pressure transducer instead of a pressure switch. And then there are the little "tankless" controllers like the Masscontrol, Prescontrol, Burcam, which also comes with a dozen other names and configurations as well. These devices use a flow switch, which is one of the worst ways to control a pump, especially a submersible.

As a side note I am helping with an Autopsy on a 75HP submersible later today. This is the third one to fail in a year. I am pretty sure we are going to find that the failure is caused by the variable speed controller, which is very common. Also nearly all well drillers and pump installers have tried variable speed pumps in their own homes. I am now hearing that while installers are still eager to sell their customers a VFD system, most have or are switching back to a standard pressure switch type system in their own homes. Even if you have your own hoist truck, all the tools, and a warehouse full of pumps to use, it is still no fun to wake up to no water coming out of the faucets.

This leaves the water in the drop pipe hanging at a negative pressure. So when the pump starts it re-pressurizes the water in the drop pipe almost instantly. The water below the upper check will fly up and hit the upper check

This is a good explanation, but I would add that in most wells, the negative pressure is enough to vaporize the water - this produces the gap in water filling the pipe. This doesn't occur with a straw (not long enough).

Since you are not using the system for domestic water, couldn't the heat pump control the well pump? I am assuming it has a solenoid supply valve that turns on/allows flow of water from a pressure system now? The signal that controlls that valve could also activate a well pump control relay. You would have to add a pressure relief valve that dumped excess pressure back to the return line, but a system such as this with a properly sized relief valve would be able to automatically compensate for changing flows in a multi-stage system without short cycling the pump...

ronmar: a key concept with a CSV is that it is more energy efficient to let pressure (as seen by the pump) rise than to dump excess flow.

samhariharan: do you have a two stage heat pump (with two exit valves such that it uses two different flow rates)?

Posted By jonr on 28 Sep 2016 11:14 PM
ronmar: a key concept with a CSV is that it is more energy efficient to let pressure (as seen by the pump) rise than to dump excess flow.

samhariharan: do you have a two stage heat pump (with two exit valves such that it uses two different flow rates)?

Yes you can do that. Like Jonr says though, it is best not to dump the excess but restrict the flow from the pump, which reduces the load and therefore reduces energy cost. Dumping the excess will quickly wear out the pressure relief valve, as they are only designed to work during an emergency. Dumping will also aerate the water, so it is not good to dump it down the well. And like Jonr says, dumping won't decrease the power load like restricting with a CSV does. You could use a CSV to control the pressure and flow to the heat pump, and still let the heat pump start the well pump (no pressure tank or pressure switch). This way the CSV would hold the same pressure when one or more heat pump zones are on. Then you can add a little pressure relief valve after the CSV. In this way if the heat pump relay started the pump but the flow line to the heat pump was clogged or the solenoid did not open, the pressure relief after the CSV would dump 1 GPM to keep the pump from melting down. We do this on irrigation systems with pump start relays. The CSV will vary the flow so that there can be irrigation zones of different sizes, and the pressure relief will protect the pump when the gophers eat the wires to the sprinklers and they don't come up when the pump is told to start. If you have a single stage heat pump the best and most efficient way is to size a pump to exactly match the heat pump demand. Then you can just let the heat pump turn on the well pump with a relay. But if the well pump is larger than the heat pump zone, or if there is more than 1 heat pump or multiple zones, the CSV will vary the flow to match what is being used. You can just let a relay from the heat pump start the well pump, but with multiple zones it is easier to use a pressure tank and pressure switch so the pump comes on automatically and the CSV matches the varying need when 1, 2, or more zones are running.

Thanks for all your suggestions and advice.
The original well contractor came by yesterday and I asked him also about CSV's and maybe going to a constant pressure pump. He has a geothermal system similar to mine but uses it for domestic water, heating//cooling and also for agriculture. He thought my system was simple enough that changing to a constant pressure pump was probably not cost effective for now. He is convinced we need a second check valve and one is not enough. Also he didn't think I needed a CSV but agreed that might help.
He thought the water hammer could be because a) the pressure switch not acting fast enough, or b) the check valve above ground failing, or c) the check valve near the pump failing. In any case, he said he would first replace the pressure switch and see if it made a difference since that was the easiest first step. He also said he thought the above ground check valve must be working since he didn't hear the water going back down. And of course, pulling the well-pump out was going to be more expensive to do.
And guess what: changing the pressure switch solved the problem for now. The system runs as smoothly as before and with no water hammer etc. Problem solved easily for now but long term I do think I might go with a CSV or other solutions.

Thanks!
Sam