Drain Pressure tank via the Pressure Relief Valve

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Tim Fastle

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I need to replace one of my well pressure tanks (has 2 32 gallon bladder tanks). The tanks are plumbed together before the pressure switch and there is a pressure relief valve but no drain valve. My plan is turn of the well breaker, run my irrigation to run the pressure out of the system and then drain the rest of the water so I install the new tank. The problem is that the tank is not in a good place to have a lot of water. The pressure relief valve looks to be adjustable with acorn nut over the adjustment screw. My hope is I can use the large outer nut (the one below the acorn nut, if indeed that is an acorn nut) to thread out the spring and adjustment rod and, as it backs out it will allow water to flow out the nozzle. I will attach a hose to the nozzle and get the water outside. (I will attach a picture)
While I have dealt with PRV in other applications I am not overly familiar with them with regard to wells. Does the one in the attached picture work like I think allowing me to take out the spring and adjustment rod, almost like a cartridge? If so, as I back it out is the water likely to start to flow before it is all the way out? A little water spillage is ok but 40 or so gallons would not be good.

Any input would be appreciated.
PRVrs.jpg
 

Fitter30

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Since the bladder is compromised just open a faucet put compressed air on it 20 lbs will be more than enough. Air will blow it out.
 

LLigetfa

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If the bladder has more than a slow leak, you could add air to the top of the tank to push out whatever water is in the tank. Just be aware that the water could be disgusting, contaminated, and have particles that could clog screens and aerators so best to drain it out a nearby hose bib.
 

Tim Fastle

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I must say, that is a very good idea and much less complicated than the approach I was thinking of. This system has two tanks next to one another. The bladder on the second tank is not broken. I have never thought about this but, with regard to the second tank, when the well is off, how much of the water in the tank will it push out - all of it, most of it half? I assume it's most of it but am not sure.
Thanks very much.
 

Tim Fastle

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On further thought, the fact that the water may be dirty and contaminated has me wondering if it might be wiser to get the water out right at the tank. There is not good way to get the water from that tank out without blowing it a long way and partially though the house. If I let all of the pressure out of the system and then disconnect the union connecting the tank to the water system I'll then have two tanks, one with a good bladder one with a failed bladder, open at the bottom but now way for air to get into the tank. Am I correct in assuming that the one with the failed bladder would likely leak or gurgle out very little water and the one with bladder might gurgle a bit more, but not a lot? I could contain that fairly easily and it might keep me from pushing the dirty water back into the system. It seems to me that, because there is not air going in, that the water isn't going to come out. Thoughts?
 

Fitter30

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I must say, that is a very good idea and much less complicated than the approach I was thinking of. This system has two tanks next to one another. The bladder on the second tank is not broken. I have never thought about this but, with regard to the second tank, when the well is off, how much of the water in the tank will it push out - all of it, most of it half? I assume it's most of it but am not sure.
Thanks very much.
Should be all of it other than what would be left in the pipe. The other tank might have some in it because the bladder might not push it all out. Still a shop vac running on a outside faucet should hold most of it back.
 

LLigetfa

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when the well is off, how much of the water in the tank will it push out
When the pressure drops to zero there should not be any water in a tank that has a sound bladder or diaphragm. I know you said bladder but I suspect it has a diaphragm, not a bladder. On diaphragm tanks, the air side has no corrosion protection hence why I said the water could be disgusting.

Sometimes water can get trapped on the wrong side of a bladder or diaphragm and cannot be drained without drilling a hole in the tank. This happens when the hole in the bladder is up high or rubber from it blocks the outlet port at the bottom.
 

Bannerman

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A little water spillage is ok but 40 or so gallons would not be good.
With the correct air precharge pressure setting (2 psi lower than the pressure switch cutin pressure = 38 psi for 40/60 pressure switch settings), each 32-gallon tank will contain only ~8 gallons water while the system is pressurized to the pressure switch cutout pressure (ie: 60 psi). The remaining 24 gallons tank space, will contain compressed air.

Each tank will contain almost 0 water at the PS cutin pressure (40). "Almost" due to the 38 psi precharge, which will cause a small amount of water to always remain in each tank @ 40 psi when the pump is activated by the PS.

With the pump's breaker shut off, drain the system. Once the system pressure has dropped to 38 psi, any further drain down will result in the pressure suddenly dropping to 0 psi, which will signify, there is no pressurized water remaining in the tanks.

Because the diaphragm in one tank is compromised, that tank's air chamber will likely, no longer contain compressed air to push water out, so some amount of unpressurized water may remain in the tank. With no compressed air in the air chamber, water may continue to gurgle out as air enters the water chamber, to replace the water that is exiting through the same connection.
 
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Valveman

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Water comes from the well and pump, not the tank. 32 gallon size tank only holds 8 gallons. It would be much less expensive and work much better to solve the cycling problem that caused the tanks to go bad in the first place than to just replace the tanks as they are. Replacing those tanks with a PK1A would save money, space, and give strong constant pressure to the showers, and make the entire pump system last longer.


PK1A Sub Pitless House.jpg

 
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