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Question DetailsAsked on 11/1/2016

What causes air pressure to slowly (over 1 or 2 days) decrease to zero?

What causes the air pressure in a precharged well tank to decreass to zero in 1 or 2 days after being properly set?

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2 Answers


1) A leak in the tank or the fill valve - obviously a tank leak in the wet zone would be expected to eventually leak water or at least show lime or iron buildup where a pinhole leak is evaporating the leaking water, but an air leak (above the bladder) would not be visible. Ditto to a leaking Schrader valve (vehicle tire type valve) commonly used on top of the tank to fill it with air and to check pressure. Check tank and air fill valve using soapy water to find leaks.

2) Tank almost full of water so there is almost no air to pressurize (water being virtually incompressible at the pressures we are talking about), so what little air there is in the tank gets absorbed into the water (if no bladder or broken bladder or slight air leak), and the pressure gets dissipated because of that. Usually you can detect the water level in the tank with hand (feels colder in water zone because of higher thermal conductivity/heat capacity of water versus air), or by tapping the tank with the handle of aq screwdriver or such and listening for the change in sound between the wet and air zones.

Tank installed upside down (if small "football" size), so air escapes into the water lines if no bladder in tank or leaking bladder so there is nothing to keep the air in the tank.

If this is a "flow-through" bladderless or leaking bladder tank (water from pump constantly flows through the tank at the bottom fitting) then if the bladder is ruptured orthere is no bladder (so air and water mix freely) the flow through the tank can constantly mix with the water in the tank and replace it with "fresh" water that is typically (being from a well) oxygen-deprived - so the air in the tank diffuses in the water and is transported out with the mixing, eventually (in a day to a week commonly) depleting all the air in the tank and leaving it full of water, so you lose the pressure-stabilization and shock-absorbing effect of the tank. With some models of bladder-free (or bladder type with a bladder leak) tanks you have to mount them on a say 4" or longer nipple coming off the piping Tee, so the water passing by the Tee does not mix substantially with the water in the tank.

Also - if the pressure in the piping drops to zero or near-zero when the pump is off (water supply system does not hold pressure) because of a leak somewhere or usage that drops the pressure but is not enough of a drop to kick the pump back on, with a ruptured bladder or bladder-free type tank the air in the tank leaks out into the water lines - till the pressure in the tank becomes just the same as in the lines. If the pressure in the lines drops to zero so does the tank pressure, then comes back up to full pressure when the pump is running.

A pressure dropoff like this can be due to leaks in the plumbing system, running toilets, leaking foot valve letting water run back into the well, etc. Though of course will only go to zero pressure if the pump is manually or timer or storage tank fill-sensor controlled (so only runs intermittently, not whenever the pressure switch detects a drop in line pressure). So, for a normal on-demand pump switch for that to happen (pressure dropping to zero) it would require that the pressure switch on the pump be malfunctioning or be mis-set - allowing the pressure in the system to drop to zero instead of kicking the pump on as soon as it reaches say typically 30-40 psi.

If you can't figure the problem out from above, then Well and Pump contractor would be the normal Search the List category for this type of diagnosis.

Answered 3 years ago by LCD



This is Erick in Member Care. Thanks for your interest in Angie's List!

We'll be happy to help find top rated providers that can look into the air pressure issues you've had with your well tank, but it doesn't look like you have a subscription to the List yet. You can join by visiting or by giving us a call. Our call center is available 8:00 am-9:00 pm weekdays and 8:00-5:00 pm ET on Saturdays.

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Answered 3 years ago by Member Services

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