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We have a freshwater bore and I recently replaced the very old pump with a 1hp Pentax pump and Trevoli 18 litre pressure tank system. For reasons I won't go into, the pressure tank has lost its precharge (nominally 2bar/30psi), and I want to recharge it. The system runs as it is, but due to micro-leaks in the system, the pump runs for 6sec or so every minute.

I want to recharge the tank to minimize the pump cycling, and I'm worried that the diaphragm in the tank is being stressed somehow without the tank air pressure to contain it as the water enters the tank.

I have a digital pressure gauge and the tank has a standard bike/car tire valve fitting on top, so I'm assuming this will be OK to check the pressure. The pressure gauge indicates sensible values on the car's tires.

I have a couple of problems:

  • I have tried putting air in with a cheap cigarette lighter adapter 12v air pump, but the pressure gauge fitted to the air pump shows the pressure ramping up very quickly towards the 150 psi tank maximum (I always turn the electric pump off way before it gets there !). In fact, it's almost as if no air is getting into the tank. Pressing down on the center bit of the valve doesn't result in the usual "pffft" and the hand-held pressure gauge doesn't show any pressure - it's almost as if the air pump is trying to pump into a dead-end. My assumption is that the valve on the tank should open and let the burst of air from the pump into the tank. The air fitting on the end of the pump has a lever-operated clamp instead of a threaded attachment: cheap battery pump and I'm wondering if this isn't allowing the valve to open (the fitting completely covers the shank of the air valve - the air fitting has a center protuberance which is supposed to depress the corresponding centre bit in the valve and I don't think the fitting can get far enough over the valve in order for this to happen and open the valve). Any comments?

  • Instructions I have read say I should 1) turn off the pump. 2) open a faucet and wait for the water to stop flowing. 3) Put air in to 2 bar / 30 psi. 4) Close the faucet. 5) turn on the pump. Should I expect the pressure tank to be empty of water after step 2 (it doesn't seem to be)?

UPDATE

I had some success with the following:

  • turned the power off to the pump
  • undid the hose from the pressure tank outlet and let the pressure tank empty out.
  • tried various methods to get air into the tank, none of which seemed to be doing anything. I couldn't get an air pressure reading off the tank.
  • connected up the hose to the outlet.
  • switched on the pump.

Remarkably, it is behaving much more like I would expect it should. Before (this is with no taps open), it was running for a few seconds every minute, now it runs for 20-30 secs every 30 mins or so, and the tank now holds an appreciable charge, i.e. it supplies water for a good length of time before the pump starts again.

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2 Answers 2

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The tank should be empty but with no air in the bladder the water may not have been pushed out. It sounds like your compressors not properly seating on the Schrader valve, I have filled pressure tanks with bicycle pumps in the past it takes a while but any pump should do the job if it has a standard valve stem adapter. Your observation that there is no pffft makes me think the supply side of that valve is not opening when attached to the tank.

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  • Many thanks for the comments. One reason there might still be water in the pressure tank is that the house plumbing is by and large above the level of the tank. Presumably, if that's the case and I can get 30 psi into the tank, will all the water will be forced out? Or do I need to disconnect the house plumbing at the tank outlet and let it drain from there before pressurizing?
    – rossmcm
    Commented Jan 9, 2019 at 19:29
  • Also: when a bicycle pump is being used to fill the tank, what causes the Schrader valve to open? Is there some mechanisn in the connector on the end of the flexible connecting tube that forces the valve open, or is it just the pressure of the incoming air?
    – rossmcm
    Commented Jan 9, 2019 at 19:37
  • @rossmcm Yes, 30 psi is equivalent to about 60 feet of water column, so as long as the open faucet is less than that high above the tank, water will come out. That actually makes it easy to see if any air is getting in at all. Also, the pressure of the incoming air should be enough to force its way through the valve, even without pushing on the central pin.
    – TooTea
    Commented Jan 9, 2019 at 19:45
  • Both, but the pin from the pump pushing on the Schrader valve provides an accurate pressure reading if only pressure is used no pin pushing on the valve you have to overcome the pressure and the small spring holding the Schrader valve closed so in that case you can add air but you don't know how much was added.
    – Ed Beal
    Commented Jan 9, 2019 at 19:46
  • Further observations. Nothing I have tried seems to put air into the tank. Bicycle pump, foot pump, electric 12v "cigarette" pump. If I close off the outlet, run till the water pump cuts off, turn the pump off, turn on a faucet, open the outlet valve, the faucet runs for a second or so - i.e. no pressure to speak of pushing the water out of the pressure tank, which feels as if it is full. Am I looking at a faulty Schrader valve (i.e jammed shut)?
    – rossmcm
    Commented Jan 9, 2019 at 21:41
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If there's no air in the bladder, the tank is full of water, and no water is running, when you try to pump it up you're trying to compress water, and the only volume elasticity in the system is from the pipes expanding-not much!!

In order to add air to the bladder, there has to be somewhere for the displaced water to go. If you empty the tank, leave the drain valve open and now add air to the bladder, it should be much easier.

In theory you want the bladder inflated to the minimum pressure that will turn on the pump, so in operation the pump will compress the bladder up to the maximum pressure, turn off, then as water leaves the tank, the pump only comes on when the tank is empty of water and the bladder fills it.

In practice you want it a little lower so the pump turns on before the tank is completely empty.

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