captive air tank and water pressure

bobcatnj

i have a kenmore captive air water tank. all it said on the tank was model 390. over the past few weeks, the water pressure in the shower seems to be lower than normal. what should the pressure be in the tank? we bought the house 2 years ago and the tank was already in place with no owners manual. the is a pressure fitting,like on a car tire, on top of the tank, i didnt see an pressure guages anywhere . we have a well and oil for heat and hot water. what else can i be?

Mike Swearingen

The air pressure in the tank should be two psi below your pump cut-on pressure (i.e. 18 psi with 20-40 psi pump cut-on/cut-off or 28 psi with 30-50 psi pump cut-on/cut-off).
With the pump turned off or unplugged and the water pressure completely drained down, check the air valve with a tire pressure gauge. If it is too high, let air out, or if too low, air it up with a bicycle pump or portable air tank or compressor.
If you get water out of the air valve, that means that the bladder is shot and you need to replace that tank.
Loss of water pressure could be from any number of other things, but the tank is first thing to check.
Good Luck!
Mike

bobcatnj

where is the pump cut on pressure guage? i looked by the tank and the well and found no guage

Mike Swearingen

There may or may not be a gauge on or near your pump.
If you have a half-horse pump, it probably is set to 20-40 psi. If you have a 3/4 hp pump, it probably is set at 30-50, just for a guess.
You can install a small 100 psi gauge near your pump. If you install it on or before your pump, it will zero down when the pump is running because that will put it on the suction (well and pump) side, then it will go to the correct pressure when the pump cuts off.
If you install it on the discharge side, it should give you current pressure readings as it goes on, pumps up, and goes off.
It just depends on where you plumb it. Most people just install it on the pump, because that is easiest since there probably is a spare 1/4" plug on the pump head that can be removed to install a gauge.
Good luck!
Mike

jwmatt

Hi Mike, It seem that you are "up to speed" on captive air water tanks. I sure could use your help. I have a cistern useing a Sears pump/tank model 390.29151, 19 gal. 20/40 cut in, cut out pressure switch. I replace the bladder, the old one had failed. When I did that I also replaced the rubber hose that comes from the bottom of the tank and tee-in to the pressure side of the pump or should I say the house supply line. That hose was 3/4". I replace with 1'. Before the bladder failed the pump would cycle 20/40 psi, just like it should. Now the max build up pressuer only tops around 36 to 37 psi. So I adjust the cut out to 35 psi. Useing 1" hose instead of going back to 3/4", is that causing my problem? The air pressure in the tank is at 20 psi. I set that when all water was bleeded off the system. This has got me puzzled. The 1" hose is the only change in the set up.