I was reading in one of the other threads that if you have two pressure tanks in one system at the same cut in pressure, it acts like one tank. I now have a 40 gal bladder tank in my well pit, with a 3/4hp red jacket pump. 30/50 pressure switch. I checked the pressure in the tank and it was good. my question is the well kicks on after 5 gallon pull down. I was wondering If I put an additional tank in my basement, how big would it have to be to draw 20 gallons of water before the pump kicks in? is there a table that would show that? 20 isn't a fixed number, but it just seems like the pump kicks in a lot.

 

This chart may be helpful.

 

A pump kicking on and off in rapid succession when running a faucet is what damages a pump. I had a pressure tank fail and the pump would kick on and off three times when you flushed the toilet. Pump failed about 2 weeks after I noticed that happening.

Your pump/tank system sounds normal to me. Remember it is not volume that turns the pump on and off, it is pressure.

 

frank are you sure your tank is 40 gallons? If so I think you should be getting more than 5 gallons drawdown. At 30-50 I believe the drawdown multiplication factor is 0.30. That is, you multiply 0.30 times the tank volume (that’s total tank volume) to get the drawdown number.

So your calculation would be 40 gals x 0.30 = 12 gals drawdown. Here is chart with drawdown factors:

Drawdown Factor Chart | WELLMATE Composite Water Storage Tanks

You can see that these factors are universal and if you apply them even to the chart in post #2 you can see they work. (Notice the WR140 in post #2 is a 44 gallon tank and has a drawdown at 30-50 of 13.6 gallons. So your tank at 40 gallons should not have that much of a different drawdown.)

I’m no expert but I believe submersible pump manufacturers state the pump should run for a least a minute when it starts. As stated earlier the start and stop is what wears the pump. Thus the tank should be sized to handle at least one minute pump run time. That is the drawdown gallons should be equal to or greater than one minute pump run time.

Did you make sure the tank pressure is set to 2 psi below the cut-in - in your case that would be 28 psi? The tank has to be drained to check the pressure.

 

Each pressure tank should be prepressurized as if it were the one and only pressure tank. Then all of the tanks together will behave like a single tank with the sum total as the volume.

 

thanks for the chart.

frank

 

you could be right about the size of the tank. I bought it at farm and fleet. the size I got was due to dimensions that would fit my well pit, hence wanting to put another in my basement to increase the volume. I have not timed my pump, but I'm pretty sure it doesn't run for a minute. thanks for the info.

frank

 

I have never had a well pump that has run for a minute except where there is heavy water usage like when using a lot of sprinklers. When taking a shower it does run close though.

 

This is one company’s view but I have seen this explanation over and over. Food for thought at least.

How to Correctly Size A Pressure Tank For A Submersible Or Jet Pump. | Doodlebug Pump