How to Size a Well Pressure Tank

How to Size a Well Pressure Tank


Hey, everybody. It’s John with Fresh Water Systems. Today, we’re shooting in our warehouse. Over the past several blogs that we’ve done
and posted, we’ve had a few people wonder if we were shooting out of our garage and
maybe that’s where we ship our items from. Well, I wanted to express to you that couldn’t
be further from the truth. We’re coming to you from Greenville, South
Carolina in our 80,000 square foot facility. We have 22,000 SKUs on hand, and by golly,
we’ve got the water treatment filters and equipment that you need for your business
or for your home. Today, we’re going to talk about pressurized
well tanks. What are they? How do they work? How do you size it? And what kind of accessories do you have to have
to make them work properly? A pressurized well tank does two very important
things. It maintains pressure in the household, so
that when you open a faucet, it doesn’t spit, it doesn’t sputter, and it doesn’t hesitate
waiting for the pump to catch up. More importantly, it protects the life of
the well pump, whether it’s a submersible or a jet pump that’s in the house, usually
next to the pressure tank. Every time the faucet gets turned on or a
shower gets turned on or a toilet’s flushed, it demands water. And these pressure tanks hold the quantity of
water to draw down before we ask the pump to kick on. And that extends the time between the pump turning
on and turning off. If that cycle time is fast, every time you
open a faucet, the pump turns on, and when you close the faucet, the pump turns off,
puts a lot of stress and wear and tear on that pump. So the most important thing that a pressure tank
does is it extends the time between the on and off cycles. The way the pressure tank works is the tank
has a bladder or a diaphragm in it and it and it separates an air chamber from where the water
goes. Well, since water doesn’t compress, but air
does, as the tank fills with water, it compresses that air chamber, and that compressed air is the energy that pushes
the water back out of the tank. We set these up to run in conjunction with
a pressure switch. The pressure switch monitors the pressure
in the tank, and it tells the pump when to turn on and when to turn off based upon the
rise and fall of that pressure. Most households are set up with a pressure
switch that turns the pump on at 30 pounds of pressure and turns the pump off at 50 pounds
of pressure. So when water is filling the tank up, when it
gets to 50 pounds and there’s a little pressure gauge on the package in front of the tank
to let you know when that is. The switch does it by itself, but the gauge helps you kind
of make sure that it’s working properly. When it gets to 50 PSI, it tells the pump
to turn off. Now, as water comes out of the tank, you’ve
opened the faucet in the kitchen or you’ve turned the shower on. As water comes out of this tank, the pressure
starts to come down and that volume of water is what we refer to as the drawdown. The pressure will continue to go down until
it hits 30 PSI, at which point the switch comes back on and turns the pump on. So that volume of water between 50 PSI and 30
PSI is the drawdown, and that’s the length of time that we’re protecting the pump from
turning on and off. Once it gets down to the turn back on part,
the pump will run until that pressure builds back up to 50 PSI. A question we get a lot is what size tank
do I need? So the three things you need to have is know
what the pump flow rate is. How fast does it pump in gallons per minute? You also need to know what the minimum run
time for that pump is. And the rule of thumb is anything under 10 gallons
a minutes should be one gallon per minute of runtime. And then multiplying the flow rate times that
one minute gives you the drawdown capacity that you’re looking for in a storage tank. Anything over 10 gallons per minute, you’re
going to calculate 1.5 for that drawdown capacity. The other thing that comes into play is the
pressure switch setting. I referred to in our last section 30/50. The pump turns on at 30 PSI, off at 50. There are three other switches that are available
in different settings. There’s a 20/40. There’s the 30/50 and a 40/60. First number is the turn back on pressure. The top number is the turn off the pump pressure. That is going to affect directly the amount
of drawdown that comes out of a tank, and most manufacturers will have a chart and tell
you what the drawdown number is based upon the pressure switch setting. So If you have a 40/60 switch, you’re going to
have less capacity than you do on a 30/50 switch. And that’s why as we get into some of those higher
flow rates, we need to calculate more of that minimum runtime. So simply put, just to go over it again, flow
rate times minimum run time gives you the drawdown capacity that you need to look for in your
pressure tank. When we sell a well pressure tank, one of
the things that we always recommend is the tee package. This is the fitting that attaches to the outlet
of the well tank and then hooks up to your inlet line from the well and then onto your
household. We recommend that you replace this, especially
if you’re replacing the well tank, because if you’re replacing the well tank because
it’s old and it’s not working well anymore, well, that pressure switch is the same age. And it’s always a good idea to replace it just
as well, especially if you’re changing brands or you’re changing a type of tank. That way the tee package is going to match
the tank and work well for you. One thing I did want to share with you, we
get a lot of questions on what’s under this little cap. Well, to be honest with you, it doesn’t do
anything. This little piece right here is used when
they powder coat the tank to hold it in the air. Other than that, they put this wonderful little
dress cap on top of it so that we can all wonder what the heck’s under there. Well, that’s all I have on well tanks. Be sure and like this video, subscribe to
our channel, and check us out on our website, freshwatersystems.com.

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