Well Pump Expansion Tank

[WinterDeere]

So, 946 pounds of pressure on a single check valve??

Is that math for the OP? I thought water ran about 0.43 per foot, so more like 300 psi for the 700 ft. rise, plus whatever pressure he's running in the house. Let's call it 340 - 360 psi.

 

[steve tym]

Is that math for the OP? I thought water ran about 0.43 per foot, so more like 300 psi for the 700 ft. rise, plus whatever pressure he's running in the house. Let's call it 340 - 360 psi.

I was referring to valveman at 2,200 foot setting. You are correct, .43 pounds per foot.

 

[Valveman]

So, 946 pounds of pressure on a single check valve??
You and I don't work in the same world.
Most check valves are designed to be operated int he full open position, not partially open. VFD check valves being the exception, but who uses a VFD check valve with a Cycle stop?

Yes, and 946 PSI is nothing for an oil field type check valve made for 3K PSI or so. Also, a pump set at 2200' needs to see 946 PSI on start up. Any extra check valves up the line would defeat the back pressure needed to keep the pump from upthrusting on start up.

You are correct a VFD check valve is not needed with a CSV. The varied flow rates from a CSV do not cause a spinning action at the pump like a VFD. Also, many VFD's like the sub/mono drive with the switch are hard on check valves as the check opens and closes every time the subdrive switch makes and breaks. This can cause a check valve to open and close 45 times a minute. For these reasons a better check valve is needed with a VFD system than a CSV system.

 

[Valveman]

Is that math for the OP? I thought water ran about 0.43 per foot, so more like 300 psi for the 700 ft. rise, plus whatever pressure he's running in the house. Let's call it 340 - 360 psi.

Yes, and if the pump was made for 700' it needs to see that 300 PSI on start up. Just need a single check valve on the pump that is rated for 300+ PSI.

 

[geteh]

That's a normal way to deliver them, but doesn't imply they shouldn't be adjusted. 40 - 60 PSI is a very common well pressure switch setting, and it's easier for a plumber to relieve a few PSI during installation, after checking with a gauge, than to haul a compressor or pump down to the basement to charge the thing. And if you're one still running 30 - 50 PSI, also easy enough to let 12 psi out thru the valve.

This doesn't apply to the OP, if he's running a constant-pressure rig, but for everyone else, this is important:

Having your tank bladder over-charged can result in both short cycling AND massive pressure losses before cut-in. Round numbers for demonstration, let's say you have a 40 - 60 PSI well pump switch and a tank bladder pre-charged to 50 PSI. Turn on the system, and the well will charge everything up to 60 PSI cut-out, before turning off. Then you use some water, and get nice linear pressure down to 50 PSI, at which point pressure in your plumbing almost immediately plummets toward zero, as the bladder is completely expanded and there's no water left to push out of the expansion tank. If you're taking a shower, you'll notice great pressure, then a total loss of water, then it comes rushing back with a bang Ants for sale UK. Not good.

Having your tank bladder under-charged doesn't cause this problem, hence the recommendation to run 3 psi below cut-in. However, going too low also reduces useable tank volume, what they call the "draw-down" capacity, between pump re-starts. This is because there is less air space remaining in the tank, when the bladder is under-charged. So, even though there's water left in the tank, there's no bladder left to push that volume.

Setting the bladder right at cut-in would maximize the draw-down capacity, but run the risk of pressure loss right at cut-in. Hence the advice to pre-charge to 3 psi below cut-in.

For OP: I've never rigged a constant-pressure pump, they weren't a thing back when my family owned a plumbing business. But I would strongly suspect that one would want to set the bladder pressure (empty tank) right at your constant pressure setting, or just a few PSI below it, for the same reasons: maximizing draw-down while preventing pressure cycling.

I ended up replacing an expansion tank on my water heater and at the same time I did the same thing on my plumbing near my pressure switch. I had thought the tank was an expansion tank. (it was a 4.8 gallon tank) I had a plumber came over and he mentioned that he thought there was suppose to be a pressure tank here instead. Is there a big difference between the 2? My well system is also a constant pressure system. I've been having problems when my sprinkler comes on my pressure gauge goes to 0 and only goes up half back to the original pressure and I can hear the bladder in the expansion tank move and the ball in the tank slams hard and makes a big thug noise every time the zones change. Could this be caused by the wrong tank installed? i drained the system and checked the pressure inside the tank. it is what its suppose to be at?

 

[steve tym]

If it's not going to the preset pressure when the sprinklers are running, the pump can't keep up for one reason or another.

 

[WinterDeere]

@steve tym already nailed it. The fact that you're never returning to at least min switch pressure indicates pump is unable to deliver what's being asked of it. There could be three reasons for that:

1. Most likely there's a damaged line or soaker ring in your irrigation system. I've punctured full 1" lines with my plug aerator, and very few residential well pumps would ever keep up with a 1" leak. You'd think this would be obvious, but if the thing is running at 4am and you're never out in the lawn before 9am, then it may not be obvious.

2. Pump is failing or at end of life, and no longer delivering what was prescribed.

3. Pump is working properly, but just undersized for scale of irrigation system.

To debug, I'd do something like the following:

1. Ensure pressure tank is adjusted properly, by shutting off water, draining system down to zero pressure, and then checking pressure on air bladder. It should be 2-3 psi below pump cut-in pressure.
2. Charge up system, bleed all air out, then check draw-down volume of pressure tank. Since most are only 10-20 gallons, you can easily do this with a few 5-gallon buckets. First, run a sink until pump kicks on, then shut off sink. Once system is fully charged and pump turns back off, start filling 5-gallon buckets until pump kicks back on. Total water dispensed into 5 gallon buckets between pump cut-out and pump cut-in is your "draw down" volume.
3. Go on internet, look up spec's for your expansion tank, and make sure listed draw down is close to what you measured, for the given pressure range. This will tell you if your pressure tank is operating properly.
4. Run irrigation system, the offending zone, and time the draw-down. If you already know the gallons, and you measure the minutes, now you know the GPM draw of the irrigation system.
5. If draw is obscene (like > 10 GPM), then start looking for a damaged or leaking line in the system. If none is found, consider splitting offending zone into multiple zones.
6. If draw is reasonable (e.g. < 6 GPM), then try to compare to your pump spec's, if available. If not available, make a guess as to pump used, based on line size and system pressure, based on your favorite pump manufacturer's design tables.

Of course, the 6 and 10 GPM benchmarks I give are for a typical residential pump setup. Commercial or farm equipment may be a whole other class, so scale the numbers to your situation, the same theory / method applies.

 

[Valveman]

I ended up replacing an expansion tank on my water heater and at the same time I did the same thing on my plumbing near my pressure switch. I had thought the tank was an expansion tank. (it was a 4.8 gallon tank) I had a plumber came over and he mentioned that he thought there was suppose to be a pressure tank here instead. Is there a big difference between the 2? My well system is also a constant pressure system. I've been having problems when my sprinkler comes on my pressure gauge goes to 0 and only goes up half back to the original pressure and I can hear the bladder in the expansion tank move and the ball in the tank slams hard and makes a big thug noise every time the zones change. Could this be caused by the wrong tank installed? i drained the system and checked the pressure inside the tank. it is what its suppose to be at?

Years ago I would see expansion tanks with a 3/4 outlet and a tiny hole inside for the water path. Any expansion tanks I have seen lately have a 3/4 outlet and a normal size opening for the water flow into the tank. If there is no tiny hole for the water flow, there is no difference between an expansion tank and a pressure tank. Just the small ones are labeled as expansion tanks as they are too small to be used as a regular pressure tank. However, with the new constant pressure systems those small tanks are as large as needed, and many pressure tanks are just labeled as expansion tanks.

Even if you got one with the tiny inlet hole it would not cause the problem you describe. As was said, using more than the pump or well can supply will cause the pressure to go low and stay low when irrigating. A break in the line is usually only on one zone.

More than likely it is a problem with the constant pressure pump, as they are not designed to be reliable, long lasting, or inexpensive. Very likely a problem with the variable speed controller or VFD is causing the pump to not get up to full speed. Amp and flow test as mentioned would determine if the problem is pump, well, or VFD controller.

BTW, the thump noise you hear happens when the system pressure drops below the air charge pressure in the tank and the diaphragm hits the bottom of the tank. Pressure should never get low enough for the diaphragm to hit the bottom.

 

[geteh]

Years ago I would see expansion tanks with a 3/4 outlet and a tiny hole inside for the water path. Any expansion tanks I have seen lately have a 3/4 outlet and a normal size opening for the water flow into the tank. If there is no tiny hole for the water flow, there is no difference between an expansion tank and a pressure tank. Just the small ones are labeled as expansion tanks as they are too small to be used as a regular pressure tank. However, with the new constant pressure systems those small tanks are as large as needed, and many pressure tanks are just labeled as expansion tanks.

Even if you got one with the tiny inlet hole it would not cause the problem you describe. As was said, using more than the pump or well can supply will cause the pressure to go low and stay low when irrigating. A break in the line is usually only on one zone.

More than likely it is a problem with the constant pressure pump, as they are not designed to be reliable, long lasting, or inexpensive. Very likely a problem with the variable speed controller or VFD is causing the pump to not get up to full speed. Amp and flow test as mentioned would determine if the problem is pump, well, or VFD controller.

BTW, the thump noise you hear happens when the system pressure drops below the air charge pressure in the tank and the diaphragm hits the bottom of the tank and **** unblocked. Pressure should never get low enough for the diaphragm to hit the bottom.

thank you so much for your suggestion

 

[Johnmash2]

Yes, and 946 PSI is nothing for an oil field type check valve made for 3K PSI or so. Also, a pump set at 2200' needs to see 946 PSI on start up. Any extra check valves up the line would defeat the back pressure needed to keep the pump from upthrusting on start up.

You are correct a VFD check valve is not needed with a CSV. The varied flow rates from a CSV do not cause a spinning action at the pump like a VFD. Also, many VFD's like the sub/mono drive with the switch are hard on check valves as the check opens and closes every time the subdrive switch makes and breaks. This can cause a check valve to open and close 45 times a minute. For these reasons a better check valve is needed with a VFD system than a CSV system.
If you’re into word games while waiting for the pump to cycle, check out:
Word List | Wordle Answer

You’re spot on — a well pump with the right check valve setup can easily handle that kind of pressure, and avoiding extra valves helps maintain the necessary back pressure to protect the pump from upthrust. With a CSV, you don’t get the same rapid open/close cycling that can wear out check valves in VFD systems.