Constant Pressure System - Pressure fluctuation

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Ericcorser

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Hi, we have a Grundfos 15SQE07 3/4 hp constant pressure pump in our 265ft well producing 15gpm. Pump is set 240ft deep. System is set at 70psi and small pressure tank is set at 49psi. System works pretty well but on the pressure gauge when water is being used the psi starts out constant at 70psi and then drops down to 60psi and then moves up to 80psi and then settles back at 70 for a few minutes and then the cycle continues. You can also hear the increased water being pushed through pipe when it pushes up to 80psi. It almost seems like pump is slowing down and then speeds up even though water usage has remained the same. We also have irrigation installed connected with T at pump and the pressure variation is seen in the sprinkler heads. Our well company has replaced the tranducer but nothing changed. Any ideas what could be going on? Thanks.
 

Valveman

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Yeah, that is the most typical problem with the SQE. The CU301 controller has lost connection with the electronics in the motor. When this happens it resorts to working like it has a regular pressure switch with 15 PSI between the on and off. I think the "newer" generation of the SQE will cycle like this 1000 times before it even shows the "lost connection" fault.

We have been solving this issue with Cycle Stop Valves since the SQE was introduced in 1999. Remove the CU301 and transducer. Replace the transducer (1/2") with a standard 50/70 pressure switch, which is 1/4" Need a 1/2 X 1/4 bushing. Then install a Cycle Stop Valve model CSV1A set for 60 PSI constant on the line before the pressure switch and tank or before any tees in the line. The pump becomes an SQ not and SQE and will be much more reliable and long lasting when using a Cycle Stop Valve.

See this link. https://cyclestopvalves.com/pages/vfd-repair-kit
 

Ericcorser

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Yeah, that is the most typical problem with the SQE. The CU301 controller has lost connection with the electronics in the motor. When this happens it resorts to working like it has a regular pressure switch with 15 PSI between the on and off. I think the "newer" generation of the SQE will cycle like this 1000 times before it even shows the "lost connection" fault.

We have been solving this issue with Cycle Stop Valves since the SQE was introduced in 1999. Remove the CU301 and transducer. Replace the transducer (1/2") with a standard 50/70 pressure switch, which is 1/4" Need a 1/2 X 1/4 bushing. Then install a Cycle Stop Valve model CSV1A set for 60 PSI constant on the line before the pressure switch and tank or before any tees in the line. The pump becomes an SQ not and SQE and will be much more reliable and long lasting when using a Cycle Stop Valve.

See this link. https://cyclestopvalves.com/pages/vfd-repair-kit
Is it possible some of the variation is due to undersized pump or do the specs I posted above look OK?
 

Valveman

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The pulsing is a symptom of the loss of connection fault. Looking at the pump curve the 3/4HP can do 70 PSI as long as the water level in the well doesn't get much deeper than 100' or so. I don't know why they would set that pump at 240' because the 100"-120' is about as deep as it can work and supply 70 PSI. Now if you lower the pressure from 70 to 40 that pump will work from nearly 200'. It is all a matter of the level in the well as to whether the pump is large enough or not. But the symptom of the water level being too deep would be that it couldn't build 70 PSI.
 
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