Modifying pressure tank pre-charge

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Bacon

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I apologize in advance - this is kind of long.

Background - we have a unique well setup at our farm that utilizes an old windmill driven Monitor ZA pump jack that is converted to run off of a 220 electric motor. We replaced the pressure tank and re-plumbed the well for a variety of reasons, but mainly because the tank was leaking air out of the top and we wanted something shorter so we could put insulation over it. This is in a ~7ft deep well pit and the previous tank was a galvanized bladder-less tank.

I just installed a 52 gallon State bladder pressure tank with all 1-1/2" piping running up to the tank. Tank uses a 1-1/4" stainless tee with pressure gauge, 30/50 switch, and pressure-relief valve. Water supply line comes off the tee and goes to the house via 3/4" copper and also via 3/4" pex to a hydrant above the well.

Everything seems to work, but I have two odd behaviors that I would like input on

Issue #1:
With pump off and tank full at 50psi, if you open the hydrant water will flow out at a ridiculously high rate - I estimate 20-30gpm. When the pressure approaches the cut-in pressure, it suddenly drops to 0 and then the pump will cycle on and off about every half stroke of the pump. Watching the pressure gauge you can see the pressure jumping between 0 and something greater than 50. I assume the hydrant flow out paces the well pump and what's happening is the tank is going completely empty. When the pump kicks on there is an inrush of water to a small area (pipes only, tank bladder is collapsed) causing a momentary pressure spike. This tells the switch to kill the pump, but then the bladder moves off the bottom of the tank and the switch again turns the pump on. It will do this forever until you turn off the hydrant at which point the well will fill up and shut off normally. If you run the shower, faucet, or any other fixture until the pressure reaches 30, the well kicks on, fills up to 50 and shuts off like it should. QUESTION: would changing the pre-charge to say 20 or 25psi instead of 28psi help prevent the completely empty tank and maybe prevent the cycling? I know it will put more water in the tank and in theory cause the well to run more, but im not terribly worried about that as this is not a main residence. I can also partially close the ball valve to the hydrant to restrict flow which should also resolve this, but that feels like more of a band-aid. The old tank never operated like this so it was odd to me.

Issue #2:
When inside the house using a faucet or even the toilet, you will sometimes notice a slight pulsing of the water. I assume this is when the well is running. This never happened with the old system, so i'm trying to wrap my head around how the new tank would cause this. The pulsing seems almost expected given the pump jack, but since the old tank didnt do this, it's a concern to my dad. Anything I should look at for this? Is it possible the old tank had such low pressure given the air leak and tiny air space in the tank that it masked the pulsing generated by the pump?

Thanks for any thoughts!
 

Reach4

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1. Yes, reducing the air precharge as you propose is a good thing. Make sure that the pressure switch senses the pressure at the pressure tank. I think you said you are using a tank tee, so no problem there.
2. That may be related to the first problem, and reducing that air precharge may solve that too.

You did not ask, but pits often get ground water. At that time, you find the well seal at the top of the well doesn't actually seal, and the ground water, perhaps from the surface, goes down the well. You can work around that by putting a utility pump, with a float switch that will trip low enough, and pump that contaminating water out. If there is a low enough spot compared to the top of the casing, you could use a sump pump instead of a utility pump.
 

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you could use a sump pump instead of a utility pump.

We do have a sump pump down there and it's always worked fine, but now that the pressure switch sits so low in the pit im worried about the float level. I may need to find something with a lower float or get a floatless pump that I turn on from time to time.
 

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It is normally the top of the casing that is the worry. But if the worry is the pressure switch, just use a longer nipple 12 inch or so would be fine. A long nipple does not cause a problem because it carries almost no flow. So there is no pressure loss.
 

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I had a 6" nipple for the switch but the tank is so wide that the long nipple makes the switch hit the tank when you thread it on. I had to go with a 1-1/2" to get it to clear. I guess I could move it away with some elbows and/or a union if it's ever an issue.

Not sure on the exact height of the well casing...which part are you speaking of specifically? And how would water get back down there? With the stroke pump isnt the top of the casing sealed around the shaft? If it wasnt, the water charge wouldnt generate any pressure to drive it into the tank.
 

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In a common well pit, the casing sticks up from the pit floor maybe 6 inches. Maybe less. The pipes enter thru a "well seal".

On my pit, the water level leveled out at the height of the casing/top and wells seal. I had scrubbed my pit with an excess of laundry detergent. When I saw suds from my faucet, I knew it was time to get the casing extended above ground and a pitless adapter installed for the pipe. My efforts to make the well seal seal had failed.

So as far as which part I am talking about, that would be the place where water could fall down the casing if the seal leaked some.

I understand that your well pump system would not be adaptable to use of a pitless adapter. So the utility/sump pump becomes more important.

can control lower than your typical float switch

But the HydroCheck switches can control even lower. With those, you set one or two probes at the level you want. With two probes, the higher one is the on-point and the lower is off. With a single probe, I presume the pump stays on for a prescribed time once the probe is out of the water. https://www.hydrocheckproducts.com/shop
 
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Valveman

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Switching from a galvanized tank to a bladder tank when using a piston pump can be problematic. The old galvanized tank was acting as a pulsation dampener. Water goes in one side of the tank and out the other. The tank cushions the pulses from the piston pump, and supplies excess water over what the pump can supply. A bladder tank is basically totally empty by the time the pump comes on, and it cannot supply any extra water over what the pump is making. The piston pump supplying water directly to the tank cross or water line instead of the inlet to the galvanized tank will cause pulsing on the water line. You will also only get as much water as the piston pump can supply. Plus, anytime the bladder tank is empty and the bladder is stuck to the bottom of the tank, the pressure switch will bounce the pump on and off as it is not getting any cushion. You maybe able to solve the pressure switch problem by reducing the air charge in the tank to 10 PSI lower than the pressure switch start point, but it will be hard to solve the pulsing and low water supply problem.
 

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Thanks valveman. Some of that makes sense, some of it is a bit confusing. To clarify, I guess I should state that we dont have a low water supply issue. I dont foresee a time we will ever actually run the hydrant so fast that it would ever drain the tank - theres no need for flow that high.

Having the inlet and outlet on the galvanized tank dampening the pulses makes sense, but the "extra water supply" part doesnt. Dont both tanks operate as a reserve volume and and pressure source? Does a galvanized tank pre-charge differ from that of a bladder? In other words, do you fill a galvanized tank with some amount of water before you set the 28psi?

My well knowledge is limited - we always had a well guy do our work, but he retired and it's just about impossible to find anyone these days so I have to learn another trade I guess :)

Thanks again
 

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On your pressure switch, consider turning the nut on the small spring CCW until the spring is not compressed. That might reduce the differential from 20 psi to maybe 18 or 19 psi. That will lower the cut-out pressure a bit. So you would probably adjust the nut on the big spring CW a bit, to keep the same 50 PSI cutout. 3.5 turns on that nut CW raises both the cut-in and cut-out pressures by about 10 psi.

The point would be to reduce the amount of diaphragm flexing that the lowered precharge will cause. The pump will be starting a bit earlier than it was.
 
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Valveman

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Thanks valveman. Some of that makes sense, some of it is a bit confusing. To clarify, I guess I should state that we dont have a low water supply issue. I dont foresee a time we will ever actually run the hydrant so fast that it would ever drain the tank - theres no need for flow that high.

Having the inlet and outlet on the galvanized tank dampening the pulses makes sense, but the "extra water supply" part doesnt. Dont both tanks operate as a reserve volume and and pressure source? Does a galvanized tank pre-charge differ from that of a bladder? In other words, do you fill a galvanized tank with some amount of water before you set the 28psi?

My well knowledge is limited - we always had a well guy do our work, but he retired and it's just about impossible to find anyone these days so I have to learn another trade I guess :)

Thanks again
Galvanized tanks don't usually have a pre-charge amount of air. They will usually continue to supply water even when the pressure drops to like 10 PSI. So, with a 30/50 switch, the tank drains to 30 and the pump starts. The tank still has some water and can continue to add to what the pump is supplying. If it is a 3 GPM piston pump and you can use 4 GPM or 5 GPM for a while as the pressure slowly drops to 10 PSI.

Bladder/diaphragm type tanks have a bag separating the air from the water. The bag is pre-charged with 28 PSI of air. When water is used the tank drains from 50 to 30 and the pump starts. But if you are using 4 GPM and the pump is only supplying 3 GPM, at 28 PSI the bladder hits the bottom of the tank and there is ZERO more water in the tank. All you will get is the 3 GPM the pump is supplying, and it will be pulsing. To do 3 GPM at piston pump does 6 GPM on stoke and then zero GPM on down stroke. Nearly any kind of piston pumps needs an accumulator or pulsation dampener, to keep the pulses out of the users system. I don't think you will ever be happy with the piston pump on a diaphragm tank.
 
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