Water pressure is low, but pressure switch doesn't turn on

[Leo Fruman]

My 3 month old irrigation pump has a pressure tank and NEW water pressure switch WITH LEVER. Intermittently, the switch doesn't turn ON after water pressure drops below cut-in level (actually to "0" ). When I force switch ON and make water pressure above cut-in level, everything works great for a while. Cut-out pressure is ~35 psi, cut-in is ~25 psi. Pressure tank bladder(?) pressure is unknown. Please advise. Regards

 

[LLigetfa]

Pressure tank bladder(?) pressure is unknown

You need to do something about that to make it known. If there is too much pressure on the air side of the bladder, the pressure nose dives when the tank is empty which then trips the low pressure cutoff. I would increase the cut-in and cut-out settings rather than decrease the air precharge.

 

[Sponsor]

 

[Reach4]

Irrigation only? You may not need a pressure tank or switch at all.

Cut-out pressure is ~35 psi, cut-in is ~25 psi. Pressure tank bladder(?) pressure is unknown.

With a pressure switch, you normally want at least 20 PSI differential. When you do have a pressure tank and switch, it is ideal if the irrigation uses an amount of water where the pressure does not rise to the cut-off while you are doing serious irrigating.

Make the water pressure zero. For a submersible pump, set the pre-charge to 2 PSI lower than the cut-in. With a jet pump, set to about 4 psi below. Your symptom would be compatible with your precharge air pressure being a little high.

 

[LLigetfa]

When you do have a pressure tank and switch, it is ideal if the irrigation uses an amount of water where the pressure does not rise to the cut-off while you are doing serious irrigating.

Eggs-act-lee. The idea is to be high on the curve to where the pump GPM matches the usage GPM but not so high that the pump can deadhead.

 

[Leo Fruman]

You need to do something about that to make it known. If there is too much pressure on the air side of the bladder, the pressure nose dives when the tank is empty which then trips the low pressure cutoff. I would increase the cut-in and cut-out settings rather than decrease the air precharge.

Thank you. I'll do that. What are the good CUT-OFF and CUT-IN pressure levels, if my pipes are PVC 1" and 2". I don't want to damage it

 

[Reach4]

What are the good CUT-OFF and CUT-IN pressure levels, if my pipes are PVC 1" and 2". I don't want to damage it

Note that white PVC should not be exposed to the sun for long periods. Paint or otherwise cover the PVC to protect it from the UV.

Normally PVC should not have a problem with 80 PSI.

 

[Leo Fruman]

Thank you guys for your comments and advises. I'll raise both CUT-OFF and CUT-IN levels, I'll make a difference ~20 PSI.
I also would reduce pressure in PRESSURE TANK if problem would not be resolved. Regards

 

[Reach4]

Thank you guys for your comments and advises. I'll raise both CUT-OFF and CUT-IN levels, I'll make a difference ~20 PSI.
I also would reduce pressure in PRESSURE TANK if problem would not be resolved. Regards

I think step one would be to measure what the current precharge is.

At what pressure does your irrigation system work best?

When adjusting a normal pressure switch, the nut on the big spring affects both cut-in and cut-out. The nut on the little spring adjusts differential.

 

[Leo Fruman]

I'm not sure how to measure current pre-charge pressure. My pump has a gauge meter attached and I can read it.
I remember it was in my pump manual, but I read it long time ago.

 

[Reach4]

I'm not sure how to measure current pre-charge pressure. My pump has a gauge meter attached and I can read it.
I remember it was in my pump manual, but I read it long time ago.

Drop the water pressure to zero. Measure the pressure with a tire pressure gauge. If you have more than one, see if they agree. If in doubt, a tire store can help tell you which one is right.

When you change the air precharge pressure, that is also done with the water pressure at zero. If there is non-zero water pressure, the air pressure would always read at least that much pressure.

 

[Leo Fruman]

Hello, Reach4. Thank you! I'll check air pressure in the tank the way you told me. I appreciate your help. Regards Leo