Pump not shutting off

[Proud]

My 2hp Irrigation pump seems to work fine for months at a time then randomly it will not turn off when no valves are open.  This will cause the water in the pump to heat to the point the pvc pipes separate from galvanized pipes going in and out of pump (2.5’ from pump).  Any help would be appreciated. Pump 2 horse, small 15”x15” +- pressure tank, 40/60 pressure switch,  1.25/50 cycle stop. Thanks, Jon 

[Cary Austin]

You need a jet pump.  Sprinklers pumps don't build enough pressure to work with a pressure switch and/or CSV.  Well, they will work with like a 30 PSI CSV and a 20/40 switch as those pumps usually have a max pressure of 42-52 PSI.  Water gets hot when running a pump too close to its max pressure.  To use a CSV125 in 50 PSI, you need a 40/60 pressure switch and a pump that has a max pressure of at least 70 PSI.  Even then you need the 50-3 instead of the 50-1 to get enough flow through the CSV to keep the pump cool.

[Proud]

Thanks!  My local irrigation supply house set me up with my current pump/ cycle stop configuration and it has worked for years except for the occasional times that it doesn’t . I think my pump must be making close to 70 psi when everything is perfect.  The pump is Franklin electric end suction centrifugal pump model cp-200-c , 3400 Rpm’s, 230 volt, 2 horse.  So I need to replace it with a 2horse jet pump?  Thanks for your help.  Jon

[Cary Austin]

I don't know how it is working at all?  Here is a link to the curve for that pump.

https://littlegiant.com/media/130644/995258.pdf

It only make 125' of head, which is 54 PSI max.  No way it is making a 40/60 switch and shutting off the pump.  Looks like that pump will still do about 25 GPM at 50 PSI even though it maxes out at 54 PSI.  You won't need a 2HP jet pump.  A 1.5HP jet pump like a Goulds J15S will pump a lot more water than that pump at 50 PSI and has a mx pressure of 80 PSI, so it works great with a 40/60 switch and will shut off as needed.

[Proud]

Thank you!

[Proud]

One more question for you.  My pump has to draw water up and over a five foot high concrete cistern with the pump being about level with bottom of cistern and 15’ away.  The pipe that draws from the cistern is 1-1/4” until the last 2-1/2’ which is 2” going into suction side of pump.  1-1/4” to irrigation valves from pump. 
Thanks again for the help.  Jon

[Proud]

I didn’t ask the question... will those conditionS affect The pump you suggested?
Thanks, Jon

[Cary Austin]

Sure a jet pump will draw from like 24' deep if needed.  However, the way you describe the suction line means there is a huge high spot before it gets to the pump.  That high spot will trap air and gulp into the pump causing a loss of prime.

If you can't draw from the bottom of the tank you should set the pump up high so the pump is the high spot in the suction line.

You could also drop a submersible in the cistern and pump up and over without any problems.