pump starts pressure drops

[Ben35]

When the well pump starts we get a momentary drop in water pressure. We have a 9-year-old submersible well pump, 85foot depth, one check valve at the pump. The problem seemed to start after the new water tank was put in, 42 gallon precharged blatter water tank, although the two happening at the same time could be a coincidence. The pressure switch is set to 40/60. After pumping up to 60 pounds the pump shuts off and the tank takes over. As water is used in the house the pressure slowly drops to 40, showing that the tank is working. But when it hits 40 pounds and the pump starts, for about one or two seconds there’s a pressure drop to 10 pounds, then right back up to 40 again, as the pump slowly builds back to 60. Anybody taking a shower gets a shot of cold water, then hot, during this pressure drop. I’m thinking the problem might be in the pump check valve. It is a 9-year-old pump.

Ben

 

[Redwood]

Set the precharge on the pressure tank to 38 PSI.

 

[Sponsor]

 

[Rancher]

Redwood hit the nail on the head, the pre-charge in the bladder tank is too close to the start up pressure of the switch.

If you don't want to drain the tank and re-set the bladder pressure, you can just use trial and error, vent the air valve for 1/2 second, then watch the cycle, if you don't get the drop, you've fixed it.

If not, vent it again.

Rancher

 

[Ben35]

I’m still learning how this bladder pressure tank works so I did a little experimenting. I shut off the electricity to the well pump and ran the water to see just how far the tank pressure would drop if the pump didn’t come on. From 60 pounds it went slowly down to 40 pounds and at 40 suddenly dropped like a rock down to zero. So the bladder must bottom out in the tank and you’re suddenly out of water pressure. I didn’t know that.

I did as you said and took some air out of the tank, first two pounds, and then another two pounds. But the same thing kept happening, sudden drop in pressure at the same time the pump started. But this time I realized that the sudden pressure drop happened a split second before the pump started. So I decided to see if I could adjust the pressure switch to start the pump at 45 PSI instead of 40 to beat the pressure drop, but it didn’t seem to be moving up at all. I was told the switch was a 20/40 turned up to 40/60 if that matters. It was also rusty and 25 years old. Maybe the old switch was getting sticky and wouldn’t come on until the pressure dropped way below 40 pounds. My 70 year old father was doing the pressure switch adjustments, which he said he’s done many times, following the cover instructions. I hope he turned the screw the right way.

Anyway, I had a new 40/60 switch on the workbench that I’ve wanted to put in. So that’s what I did. I adjusted the tank to 38 pounds and put in the new pressure switch. It worked great! No water pressure drop. The new switch turns the pump on at 42 pounds and off 60. That’s where I stopped for the day because I was just glad to see it working.
Thanks for the help and great site.
Ben

 

[Rancher]

A 20/40 switch turned up to 40/60 may be at the upper limit of adjustment.

Rancher