Domestic well with pressure drop problem

[stevo_61]

This small (I think 1.5hp) above ground domestic water centrifical pump will pump up to 78psi. As water is used, the pump drops down to 68psi where it then very quickly drops and the pump starts up and goes back up to 78psi. The bladder tank will range from 38 to 45 psi during a cycle. The problem is the quick drop in pressure that lasts for about a second in the house. I know the air pressure in the bladder should be about 5 psi under the minimum water pressure, but if I add any more air, the pump will buck a few times before it starts. I cleaned the contacts. The pump sounds like it is operating normally. It worked fine for the 14 years we have lived here. The motor was replaced about 6 years ago due to lightning strike. Any ideas?

 

[Valveman]

You must have a bad gauge because the pump pressure and the pressure at the tank should be the same. However, it sounds like the bladder in the tank is bad and the tank is water logged.

 

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[stevo_61]

Thanks for the reply

The water pressure guage right off the pump is pretty rusted. I will replace that but I am afraid to break the prime. I had a heck of a hard time getting it to prime a few years ago when I replaced the pump. The air tank is only about 2 years old. If the tank was broken or puncured in some way, wouldn't water come out the air valve?

 

[Bob NH]

Here is a way to set it without a usable gauge on the water side.

1. Decide what pressure range you want to operate over. I suggest something like your existing starting pressure but increase the shutoff pressure to at least 15 psi greater than the starting pressure.

2. With pump power off, run all of the water out of the tank.

3. Put air in the tank to 2 psi less than you want for start pressure, using the tire gauge.

4. Run the pump for 5 seconds to put some water in the tank. Add or remove water (pump or drain) as necessary to get the air pressure to 2 psi greater than your precharge.

5 Adjust the pressure switch so it is at the START point. You can do that with the power off by first increasing the pressure setting (tighten the screw or nut) until the switch stays in the OFF position when you lift the plate at the bottom of the switch. Then, back off on the switch (lower the pressure setting) until the switch trips to the START position.

 

[NHmaster]

What is the pressure switch set at? With a 20 degree differential say 30lbs cut in and 50 lbs cut out the tank pressure should be at 28lbs.
It sounds to me like the tank bladder is ruptured and you are working off whatever air got trapped in the top of the tank. A easy way to check is to shut the pump off, draw all the water pressure down and then open the shrader valve. It may take a bit to get the air out but if the air goes and then you get water, the bladder is bad. If not, re-charge the tank 2lbs below cut in and change or adjust the pressure switch.

 

[Gary Slusser]

The water pressure guage right off the pump is pretty rusted. I will replace that but I am afraid to break the prime. I had a heck of a hard time getting it to prime a few years ago when I replaced the pump. The air tank is only about 2 years old. If the tank was broken or punctured in some way, wouldn't water come out the air valve?

You usually have problems priming when there is a bad foot valve in the well or some other leak. That would also explain why this sudden drop in pressure as the possibly sticking foot valve pauses before closing.

Do you ever hear the pump run when there's no water being used? If so that proves a leak and you should shut off the water past the pressure tank and see if that stops the pump from running. If so, the leak is back between the tank and the foot valve in the well. If the pump didn't run, the leak is on the house side of the tank.

So what problem did you have priming the pump? Is it really a centrifugal pump, or is it a jet pump?

I think you need to adjust the air in the tank properly. That 5 psi or whatever it truely is, is probably the reason for the 78 to 68 drop.

The air psi has to be 1-2 psi less than the cut in setting, that's with no water in the tank.

 

[stevo_61]

Thanks, problem solved

My water pressure guage was way off. It was reading 60-80 psi when the actual pressure was 27-47 psi. This caused me to over pump my air bladder which must have caused my problem. I put the bladder tank to 27 psi and the problem is gone.

 

[Gary Slusser]

The air psi has to be 1-2 psi less than the cut in setting, that's with no water in the tank.