anyone using a cycle stop valve?
 

As some of you know, I use open loop (aka "pump and dump") geothermal heat pumps for heating/cooling the houses here on the farm and for water to livestock (for drinking) and for irrigation. Well water supplies the geothermal heat pumps and the exit water is used to fill ponds that I then use for pasture irrigation.

A 2 HP pump could never meet the volume demands of irrigation alone, so I fill ponds and then use a much larger centrifugal tractor PTO pump to supply the needs for the irrigation system (needs about 200 gpm).

Anyway, I use a deep submersible pump (2 HP) down in a well about 180 feet. This will provide about 30-35 gallons per min of water. To minimize short cycling of the pump, I use two 85 gallon bladder tanks in parallel. Two, because if one fails, then I have the other to prevent short cycling of the pump. Standard 40-60 psi pressure switch.

Extreme short cycling a water well pump can (and will) kill a pump in just a couple days.

One of the pressure tanks just lost the bladder and replacing it is ~ $400. A plumber friend suggested putting in a cycle stop valve to further minimize cycling of the well pump and to forget about replacing the broken bladder tank.

With the exception of spring and fall, this water well pump runs a lot and I suspect that even with the bladder tanks, I have hundreds of cycles on the well pump per day. Well pumps are like an incandescent bulb - lifetime is largely a function of the number of start/stop cycles.

Also, replacing the pump is expensive, tough to do physically and it seems like well pumps always fail on a day when I need water for livestock or it is below zero . . .

The cost of a cycle stop valve is < $100 and if it does what it says, then putting one in is a no brainer. Here is the URL of the manufacturer and am interested in the group's thoughts.

Cycle Stop Valves, Inc.

Thanks in advance!

Steve

The interactive graphic on their website leads me to believe the CSV is a flow modulated throttling device. It reduces pump output by raising back pressure to the end of the pump curve where motor current goes down.

My first concern would be that a centrifugal pump can boil water at this end of the curve. Submersible pumps depend on flowing water to cool the motor. Perhaps it isn't a problem but I would ask the manufacturer to address this.

I addressed the short cycling problem on my submersible by using a smaller pump and larger bladder tank. This may not be an option if your short term demand is high.

Doug

Doug,

You are exactly correct. Boiling water is not a concern as the low end of the pump is about 1 GPM. I put one in on my cousin's house (also a well source, open loop GT heat pump). He has livestock also and he allows water at about 1-2 GPM to fill livestock water tanks.

The well pump never shuts off! But the pump current does go way, way down.

Was hoping someone here had also used one.

Steve

Maybe try a delay on break timer? They're about $10 or so at a HVAC supply store and are simply wired in series with the contactor coil. They don't do anything until the control circuit tries to short cycle, at which point they enforce a minimum off time.

Adding restriction would reduce efficiency.

NiHao,

I wish I knew if efficiency went down, up - or stayed the same. There is no question that my deep well pump cycles many hundreds of times a day. Pump data clearly shows that there are only so many off - on cycles before failure occurs.

The critical question is: will prevention of short cycling extend pump life?

I do know, because I measured it, that a restriction in the outflow water line decreases pump current linearly proportional to water flow. In contrast to a constant volume displacement pump (think pistons here), a centrifugal pump does not exhibit afterload effect.

In the long run, does longer cycling extend pump life? If so, that is a BIG issue as pulling a pump and replacing it is a MAJOR pain in the *** as well as expensive.

Steve

Deep wells pose a particular problem for pumps. First, the pressure at the pump is the sum of static pressure at the bladder and the head pressure of the standing column, in your case 180ft.

I think the bigger problem for the motor is the inertia of the standing column of water in the riser. The effect is like a very large flywheel. Deep well pumps are expensive because they are made to withstand high starting loads. But even a well built motor doesn't like hard starts.

One possible solution to short cycling is to pump the water into three or four 275 gallon totes (or similar reservoir) at the surface and then use a small pump to distribute it from there. The well pump is controlled by a level switch with considerable deadband. The surface pump responds to pressure from a bladder. Low pressure centrifugal pumps stand up well to short cycling. Both pumps are thus operating under optimum conditions.

The delay on break will prevent short cycling. Depending on the pressure rating of the plumbing, also try increasing the cut out pressure and/or decreasing the cut in pressure.