Pressure Tank Problem

[steelepulse]

I have underground water storage that is pumped via two pumps and with a pressure tank delivering the water to the house. Recently the pressure tank seems to be losing pressure quickly and causing the pump to start and stop 3 times before stopping for maybe 30 seconds before the whole cycle is repeated again. In the past the pumps would turn on, stay on for maybe 5 seconds, then stop and not turn on until water was used and pressure dropped.

I do have an air valve at the top of the tank and when pressing the valve water immediately comes out. Is this the way it should be or should there be a bit of air in the pressure tank?

I'm sure this starting and stopping frequently isn't helping the longevity of the pumps nor on the electric consumption. Any ideas? BTW I have separate water pressure regulators for each pump, anything to do with those perhaps?

[Naam]

Is this the way it should be or should there be a bit of air in the pressure tank?

you are on the right track. your pressure tank lacks air.

[gusG]

You also could need a new internal bladder, in the tank.

[Crossy]

Something like this to get the air back in to your tank.

Turn off the pump, and close the pump outlet valve.

Open the drain at the bottom of the tank and the air valve on the top.

When the water stops coming out close the drain and air valves.

Open the pump outlet valve and turn on the pump.

The pump should run until the pressure builds up and all should be normal again

[LennyW]

Is it a separate pump and pressure tank? does the pressure tank have a valve on the top similar to a car tube valve? i will show you pics in daylight but if your pressure tank does have a valve on top then you can check your pressure, not sure your size but i have a 40 Litre and a 60 Litre system and both are supposed to be at around 24 Psi.

[Delight]

A bladder tank is installed in a domestic water system to cope with low demands for water. If the switching of the pump relied on a simple flow switch then the pump would be ‘on ‘ and then immediately ‘off’ as per low demand water consumption.

When the pump is running it pressurizes the water in bladder tank and this in turn compresses the air in the bladder. Sensors detect the ’full tank pressure’ –typically 2 bar (30p.s.i.) and stop the pump.

This pressurized tank and compressed bladder then ‘push ‘ water to satisfy demand(pump not running). This results in a drop of water pressure .. At typically 1.4bar (20 p.s.i.) a separate sensor detects this lower pressure and starts the pump . When the demand for water is at an end, the pump continues to run until the’ full tank pressure ‘ is sensed at which point the pump stops. The system is now ready for the next demand for water. This means that the pump will always run for minimum ‘healthy ‘time.

I would suggest that you purchase a motorbike foot pump,(sufficient air hose such that the pump can be connected to the air valve and be adjacent to your foot at the same time)and a good quality tyre pressure gauge –one where the needle stays at the measured pressure value. Both are low cost.

You need to see that the air in the bladder will be retained (try about 14 bar (20 p.s.i.)when the system is not working i.e. isolate both the pump and demand.

If this is not achievable then its bladder replacement time.

If it is then it is just about setting the values (Bladder pressure –full tank pressure (pump stop)-low pressure (pump start).

The tank manufacturer will be able to supply these values .

Note:There could be other components in system which are mis -functioning and causing the problem -check valves etc.

Edited October 30, 2012 by Delight

[Naam]

You also could need a new internal bladder, in the tank.

only if his tank has a bladder. most pressure tanks do not.

[Crossy]

Our OP notes that water comes out when he opens the valve on top of his pressure tank, so any air that remained has now exited.

Most likely he does not have a bladder and even if he does and it's ruptured, draining out the water from the tank with the pump off will get things working again.

[Delight]

You also could need a new internal bladder, in the tank.

only if his tank has a bladder. most pressure tanks do not.

I am curious how a 'Pressure ' tank can work without a bladder (or an internal diaphragm).Without either the tank can be pressurized -but will immediately lose pressure as soon as any demand for water occurs.

This describes the symptoms of the O.P's problems.

He either fixes it himself -as detailed in my earlier post -or gets a bladder repair/replace man in

Edited October 30, 2012 by Delight

[handydog]

You also could need a new internal bladder, in the tank.

only if his tank has a bladder. most pressure tanks do not.

I am curious how a 'Pressure ' tank can work without a bladder (or an internal diaphragm).Without either the tank can be pressurized -but will immediately lose pressure as soon as any demand for water occurs.

This describes the symptoms of the O.P's problems.

He either fixes it himself -as detailed in my earlier post -or gets a bladder repair/replace man in

Older style pressure tanks are simply larger (taller) in size and many did not have a bladder fitted. The air cavity is created by having the water in and the water out pipes close to the bottom of the tank (outlet 6 ish inches above the inlet) and this allows the space above to facilitate the air cavity. The downside of this style of tank is the air does over time becomes disolved in the water and the water level rises... necessitating the need to drain the tank. On a house pump expect to do it monthly, but this depends on how much it is used....

The use of a bladder containing the air, allows the tanks to be smaller overall and the need to drain them less frequent. Bladders do wear out and will leak (air) with age.

[steelepulse]

Something like this to get the air back in to your tank.

Turn off the pump, and close the pump outlet valve.

Open the drain at the bottom of the tank and the air valve on the top.

When the water stops coming out close the drain and air valves.

Open the pump outlet valve and turn on the pump.

The pump should run until the pressure builds up and all should be normal again

That did it. Thanks Crossy!

[Pib]

You also could need a new internal bladder, in the tank.

only if his tank has a bladder. most pressure tanks do not.

I am curious how a 'Pressure ' tank can work without a bladder (or an internal diaphragm).Without either the tank can be pressurized -but will immediately lose pressure as soon as any demand for water occurs.

This describes the symptoms of the O.P's problems.

He either fixes it himself -as detailed in my earlier post -or gets a bladder repair/replace man in

Older style pressure tanks are simply larger (taller) in size and many did not have a bladder fitted. The air cavity is created by having the water in and the water out pipes close to the bottom of the tank (outlet 6 ish inches above the inlet) and this allows the space above to facilitate the air cavity. The downside of this style of tank is the air does over time becomes disolved in the water and the water level rises... necessitating the need to drain the tank. On a house pump expect to do it monthly, but this depends on how much it is used....

The use of a bladder containing the air, allows the tanks to be smaller overall and the need to drain them less frequent. Bladders do wear out and will leak (air) with age.

Usually the bladder type does not contain the air; it contains the water....kinda like filling up a balloon with water and then squeezing it with your hands to force out water...with your hands simulating pressurized air in pressure tank surrounding/pressing down on bladder. Besides the prime purpose of helping to create an energy source/cushion/spring to push out water when the pump is off, this approach accomplishes two other main purposes of a bladder-type tank: 1) keeps the water and air from making contact in order to stop the air slowly being absorbed into the water causing a tank waterlogged condition and, 2) ability to use metal tank material which doesn't have to be rust-proof/keep the water from contacting the metal. And a diaphragm-type tank does the same job of keeping the water separated by having a rubber barrier between the water and air.

The larger pressure tanks I've seen in Thailand do not have a rubber bladder/diaphragm...they are just solid stainless steel which don't rust (or take a very long time to rust) with an air valve in the top to periodically recharge air...and the better setups come with an air control valve installed in the upper part of tank which automatically adds just a little air to offset the air being naturally absorbed into the water. And if it's an irrigation pressure tank, it probably won't be stainless steel but instead some other metal which won't last as long but there is no concern if a tiny amount of rust gets into the irrigation water.

Basically the same principle used with a very common house-hold pump sold all over Thailand where the pump assembly sets on top of a small pressure tank around 15-20 liters in size and there is an air control/balance valve which feeds a little bit of air into the tank each time the pump cycles on and off. And when this air control valve stops working properly (like mine did before) within about two weeks the tank will be water logged with the pump will rapidly cycle with a tap on...say with a tap on the pump will mostly run and maybe turn off for a second and then start running again..cycling that is 90% pump run and 10% pump off when is should be more along the lines of a 50-50 affair.

Here's a Link that may be helpful in analysing/repairing a pressure-type tank.