Expansion/pressure tank question

[HilltopDaisy]

Could someone explain to me what this is exactly, and how it works? I live in a trailer and this thing sits in a closet. I will be taking it out and putting it in the cabin in a couple of months. I just want to understand it's purpose. Thanks.

[DYngbld]

I assume you are on a well.

Our pressure tank is under the house. The well pump itself does not have the pressure required to supply the house with proper pressure. This tank provides the water pressure needed. THere are a couple of different kinds depending on what type of well you have.

[T-Bone 369]

It's function is to maintain pressure in the system when the pump is off.

Think of it like this - Water come in from your pump and passes through a check valve so it can not get back out into the well when the pump is off. Beyond the check valve is the pressure tank. Inside the pressure tank there is a balloon. As the pump works it compresses the balloon - as you know fluids do not compress under pressure, air does. When the pump reaches the cut off point (the set point where the max water pressure is) is shuts off. The water can not escape back into the well because of the check valve so the bladder stays compressed. As you draw water (turn on a faucet for example) the bladder starts to expand back to it's larger size forcing the water to continue to flow. When the pressure reaches the cut in point (the set low pressure) the pump restarts and re-compresses the bladder by adding water to the pressure tank. Simple as that.

There are other ways to maitain water pressure - gravity fed (think water tower) and on-demand (many RV's have this system - the pump has a constant pressure switch that runs the pump whenever a tap is opened). But most wells use a pressure tank system. Hope that helps.

[Windy in Kansas]

"The well pump itself does not have the pressure required to supply the house with proper pressure."

This isn't quite right as the pump itself is what pressurized the tank in the first place.

The bladder tank is in the system to hold water under pressure from the bladder full of air. This way the pump doesn't have to run each time you need a teacup full of water. This brings up the point---get the largest tank you can afford so that the pump isn't cycling on and off as much. In your case it will be a matter of moving the current tank.

An expansion tank is really an entirely different kind of tank that is generally used in hot water heating systems. I'll not bother to explain more.

In addition to what T-Bone already wrote about other systems, some campers, especially older ones used air pressure to move the water rather than an on demand pump. A diaphragm pump forced air into a water storage tank and served similarly to a bladder tank

Another type might be to use a gravity flow overhead tank and then use a booster pump to raise the pressure higher. Sort of a waste in some respect as the well pump might just as well pump into a bladder tank to create the pressure. If using a windmill, a spring to feed the gravity tank, etc., then yes a booster pump might be warranted. This Old House show installed one a while back in a house with low city water pressure.

Another type of water system is the shallow well pump. As indicated shallow water is a must. The ones I've been around, which is only a few because of deeper water, also use a bladder tank.

At my farm I have a submersible pump to bring forth water from the well. I have no pressure tank at all and no storage. I have water when the pump runs and none when it doesn't. Since it is used for garden irrigation that really isn't much of a problem.

I haven't decided whether I'll eventually add a bladder tank or perhaps install an overhead tank with gravity flow system. I lean toward the latter so that a person can still have a good and ready water supply even if the electricity goes off.

[TnAndy]

Originally Posted by DYngbld

I assume you are on a well.

Our pressure tank is under the house. The well pump itself does not have the pressure required to supply the house with proper pressure. This tank provides the water pressure needed. THere are a couple of different kinds depending on what type of well you have.

Nope....you don't understand a pressure tank....the pump provides all the pressure in the system.

See T-bone's explanation.

[Old Vet]

Originally Posted by Windy in Kansas

"The well pump itself does not have the pressure required to supply the house with proper pressure."

This isn't quite right as the pump itself is what pressurized the tank in the first place.

The bladder tank is in the system to hold water under pressure from the bladder full of air. This way the pump doesn't have to run each time you need a teacup full of water. This brings up the point---get the largest tank you can afford so that the pump isn't cycling on and off as much. In your case it will be a matter of moving the current tank.

An expansion tank is really an entirely different kind of tank that is generally used in hot water heating systems. I'll not bother to explain more.

In addition to what T-Bone already wrote about other systems, some campers, especially older ones used air pressure to move the water rather than an on demand pump. A diaphragm pump forced air into a water storage tank and served similarly to a bladder tank

Another type might be to use a gravity flow overhead tank and then use a booster pump to raise the pressure higher. Sort of a waste in some respect as the well pump might just as well pump into a bladder tank to create the pressure. If using a windmill, a spring to feed the gravity tank, etc., then yes a booster pump might be warranted. This Old House show installed one a while back in a house with low city water pressure.

Another type of water system is the shallow well pump. As indicated shallow water is a must. The ones I've been around, which is only a few because of deeper water, also use a bladder tank.

At my farm I have a submersible pump to bring forth water from the well. I have no pressure tank at all and no storage. I have water when the pump runs and none when it doesn't. Since it is used for garden irrigation that really isn't much of a problem.

I haven't decided whether I'll eventually add a bladder tank or perhaps install an overhead tank with gravity flow system. I lean toward the latter so that a person can still have a good and ready water supply even if the electricity goes off.

He should have said volume to the sink in stead he said pressure. You pump will have enough pressure to fill the tank but not the volume to keep it at full pressure for very long.

[HilltopDaisy]

So the water enters the tank from the well; then the water goes to the hot water heater from one line and to the faucet/s from another? And does the tank require electric?

[DYngbld]

Yes, sorry water VOLUME. I just got a well this past year so I am still learning on the in-and outs of it myself. The well pump does have the pressure to fill the tank. I think it is something like 11Psi on tank under the house. The old well on the trailor we lived in while building the house had a different kind of pump. Mine is a submerged pump, the other one is above ground jet pump. (don't let it loose prime).

Yes I stand corected, (as usual). The tank suplies the water volume needed. Mine is also nice for small supply of water after the power goes out. Now on to something else to be wrong about.

[jross]

Originally Posted by TnAndy

Nope....you don't understand a pressure tank....the pump provides all the pressure in the system.

See T-bone's explanation.

That is not quite true either, since the tank is pre charged with air. The tank air pressure is to be set with the pump off and at the required pressure which depends on the pressure range you want the pump to operate at and is usually posted on the tank. The air pressure setting is important to maintain the life of the system. After the air is set, the pump maintains the operating pressure of the system via the cut in and cut out settings.

[Windy in Kansas]

Originally Posted by HilltopDaisy

So the water enters the tank from the well; then the water goes to the hot water heater from one line and to the faucet/s from another? And does the tank require electric?

Well water goes to the tank. From there a cold water line basically takes it to all cold needs which includes the cold supply side of the water heater, outside faucets, etc. A water heater tank will be marked at the inlet and outlet which should be used for cold and for hot. The cold side has an interior pipe taking the cold supply to the bottom so it is closest to the burner if I remember correctly.

Where the water heater is located in the run of the cold water pipe really doesn't matter as a hot water line then goes from the water heater to all of the hot needs such as faucets, dishwasher, shower, washing machine, etc.

The bladder tank itself does not need electricity. However a pressure switch on it is used to control the well pump electricity on and off cycling so there is electricity to the tank even if it doesn't itself use it.

[dpdee13]

We have an older pressure tank (late 70's) pre-bladder model. These older pressure tanks can become "water logged". There is a test you can run to determine how your pressure tank is doing. Depending on tank size and high/low limits you should be able to get x amount of gallons of water from the tank from high limit until the pump kicks on.

I have to recharge our tank approx. every two years. Shut off pump and water supply line to tank. Open valve above tank and bleed all water from tank using valve on the bottom of the tank. Close all valves, fill tank with air to 38 psi (our tank has 40 psi low and 60 psi high) using schrader valve at bottom of tank then turn pump on. After this procedure there is a noticeable increase in the amount of water available between the high and low limit.

I normally run water through the closest valve to the tank until the water runs clear after doing this. The recharge process stirs up sediment that collects on the walls and the base of the tank.

Dave

[fordy]

................If , your tank has a valve stem on top , it has an air bladder ! If yes , to set the air pressure correctly.....a)drain all water from the tank , this allows the bladder too expand too its proper size without any water in the tank , b)check pressure with a regular tire gauge , then inflate the bladder to 2 psi less than the low side , kickin pressure of your pressure switch . Ex. , so IF your pressure switch kickin pressure was 40 psi , you'd inflate your bladder to 38 psi . , c) Once you set the bladder pressure simply turn the Pump back on and it will fill the tank as it should . , fordy