Tank Size

[bobabuoy]

I have recently been upgrading the plumbing on my house and now feel it is necessary to replace my water tank. Currently the water tank is in a pit under my house which is currently leaking from one of the galvanized pipes. The tank is practically inaccessible, and is in a totally unsanitary area if I need to redo the piping. The problem is that I don't know what size tank to replace it with. My current tank is probably galvanized and not bladder (I emptied it and blasted the water out with compressed air). I don't know what size it is. I also do not know what size my submersible pump is. How can I determine what size tank to replace it with?

[Bob NH]

First you must find the flow rate of the pump. If you can find the model number it is usually possible to find the flow rate.

Another way is to measure it when the flow is steady. Connect a hose to an outside faucet near where your pump comes into the house. Turn off all the other water in the house and then turn on the hose. When the pump comes on, close down the faucet until the pressure (you do have a pressure gauge) remains steady somewhere within the range of the pressure switch.

Now measure how many seconds it takes to fill a 5 gallon bucket (5 gallons is usually about 2" from the top). The Gallons per Minute of your pump is 300 divided by the number of seconds to fill the bucket. (I'll bet you never thought you would need long division).

Pick a bladder tank that has a real volume of about 5 times the GPM of your pump. That will give you a cycle time of about 90 seconds with a 30 to 50 psi pressure switch setting. A smaller tank, 3.3 times your pump GPM, will give you about 1 minute cycle time. That is the smallest I would ever go.

Make the seller show you the REAL VOLUME, not the strange numbers that they quote for "galvanized tank equivalent".

When you install the tank, pressurize it with air to 2 psi less than the ON setting of your pressure switch. Make sure your tire gauge and your water pressure gauge give the same reading when there is water in the tank.

[bobabuoy]

Thanks. That's great. I can definitely do that to measure the flow rate. I don't think I would have been able to get the pump out of the well without causing a huge headache.

Do installers ever write the pump information somewhere visible? Maybe inside the well cap?

Thanks

[Bob NH]

They should leave you with a manual and tag that gives you the model number of the pump, and the well driller should leave you with complete information about the well. Some responsible drillers and/or pump installers will put a permanent tag on the well head or other conspicuous place that includes all of the information about the well and the pump.