We have a 76 liter diaphram well tank that serves our irrigation system. It has been cycling on and off for a while. When checking the pressure via the Schraeder valve it was reading off the pressure gauge (way over 50psi.) The factory psi is 28 and the working psi is 100. I turned off the well pump power, drained it and checked the pressure on the schraeder valve which now read 12 psi. I filled the tank with air to 28 psi. I turned the power back on, the tank filled with waterand I checked the pressure and again it is reading way off the gauge - too high - it also cycled on and off immediately - the irrigation system is off. Am I doing something wrong? Any suggestions?

 

Don't worry about the pressure when the pump is running. The only pressure you need be concerned with is the empty tank pressure which should be two pounds less than the pump cut in pressure.

Now, for water pressure...what is the pressures when the pump cuts in and cuts out? Be sure you are not losing water anywhere in your irrigation system. And, be sure your check valve is not bad allowing the water to return back to the well.

 

Could you please explain to me the tank cut in and cut out pressure? When and how can I determine these?

 

With your pump operating in the normal mode, stand at your tank where you can see the water pressure gauge. Open a water faucet (or have someone open one somewhere) and watch the pressure gauge. When the pump starts record the pressure. That is the "cut in" pressure. Close the water faucet. Watch the pressure rise as the tank fills. When the pump stops record the "cut out' pressure.

When the pump stops (or even before) close the valve at the tank that feeds your irrigation system. Does the pressure immediately start to drop? If so then you most likely have a bad check valve between your pump and your tank.

 

The tank has the Schraeder valve which shows the tank pressure and then a dial gauge which shows the working pressure (right?) I figure that's the case. I'm no expert though THAT is for sure. Anyway, when I did as you stated, the tank cut in at 60 psi and cut out at 76 according to the working pressure dial gauge. When it stopped, I closed the valve that feeds the irrigation system and the pressure on the working gauge did not immediately drop. Any ideas? Thanks for your time.

 

Ok, here is what's happening.

The diaphram in your tank has 28 pounds of pressure behind it. But your pump cuts on at 60 psi. That means that your tank is only using a very small amount of the available room in the tank to store water. It takes 40 liters of water just to pressurize the diaphram from the preset 28 pounds to 60 pounds. That is the point the pump cuts on, so you are only storing 36 litres of water, max.

You want your tank to expell as much water as possible before the pump cuts on. Therefore, you want the diaphram pressure to be 2 pounds less than the pump cut in pressure.

Either reduce your cut in pressure to 30 or raise the diaphram pressure (pump off and no water in tank) to 58.

Then you will be using 70+ liters of water from your tank before the pump cuts in.

You need to decide if you need 60-75 pounds or pressure, or if 30-50 is sufficient for your needs. How much area is being serviced by that irrigation system?


(Geez I hope those figures are close...top of my head numbers)

 

We need the 60-75 pounds of pressure to service the irrigation area for sure. We've owned this home for nearly three years and this pump didn't cut in and out like this (couple times an hour) until about a month ago. The pump is located on the other side of the wall our bed sits against so I can hear it go on and off all the time. How did this state of affairs occur? Does it just happen over time? I know this pump is 5 - 6 years old. By the way, would you now re-read my first post on 5/18 at 11:34 am (it addresses the tank psi as shooting straight up as soon as I turn the power to the pump back on after I have just drained it and reset it to 28.) I just want to make sure we are on the same page because the tank pressure definitely doesn't stay at 28. I hope I'm making sense!! THANKS SO MUCH FOR YOUR HELP. I am learning a lot.

 

You are making perfect sense. And yes, the pressure on the tank schrader valve should ONLY be checked when the pump is off and absolutely NO water is in the tank.

When the tank fills with water then there will be a substantial rise in the pressure, But, that is only relevant if it exceeds the maximum rated pressure in the tank.

Over time two things could happen to create the symptoms you describe. First, schrader valves are not absolute. They do seep a little air out over time. You wouldn't know it except for the amount of time the pump cycles.

And two, the diaphram could have a pin hole in it allowing a liitle air out, but more important, letting water in. If you suspect that then the only check is to turn off the pump, then drain the air through the schrader valve. If any water comes out then you can suspect a bad bladder.

When you go back (after finding no water in the bladder,) you should first drain the tank completly, and put 58 pounds of air in the schrader valve, then turn your pump on and you should be good to go.


Can you check to be sure the tank is rated for the pressure?

 

Here are the specs right off of the tank...

Total Tank Volume: 20 gal.
Maximum Working Pressure: 100 psi
Tank Precharge from Factory: 28 psi
Drawdown at 30/50 psi

Can I move ahead with what you suggested?

 

Yep. Sure can.

 

I drained all the air from the tank from the Schraeder valve and no water leaked out. I then followed the instructions and put in 58 psi air into the tank. It took about 15 minutes and then cut in again right at 60 psi. When it does that, the pump runs for just about 10 seconds and then the pressure on the dial immediately starts to climb back up to the cut out at 76. Could there be a leak? What/where is the check valve? Is there a limit on these threads? I suppose I've way surpassed mine! Thanks again.

 

No, it sounds normal actually. You are actually raising the pressure by 16 pounds. A good pump will do that in a short time. Especially in a 20 gallon tank. As long as you do not lose pressure when no water is being used then you should be good to go.

What are the capacity requirements of this irrigation system? Are you irrigating crops or watering a lawn?

 

I'm thinking we might have a leak somewhere in the irrigation system..We are just watering a lawn and bushes and stuff on an 11,000 sq. ft lot - house in the middle of course. Anyway, last night I turned off the power to the pump all together because our irrigation system (which is on a timer) does not run on Tuesdays. When I went out to check it this morning, the tank was completely empty, working pressure was 0 and the pressure inside the tank was around 31 psi. I'm not an expert for sure (that's GOT to be obvious by now..) but it the irrigation system was completely off and the pump power was turned off where did the water that was in the tank go? Is it time for me to call in the troops?