Many of you may not know this but there is a war going on within the well industry, a silent war, raging on for decades – this war has pitted fathers against sons and brothers against brothers, I’m speaking of course of the war between galvanized tanks vs bladder tanks.  Dun, dun, DUN!!!

It’s really not that dramatic but a rift does exist – Companies who use old, heavy, hot, ugly, cumbersome, galvanized pressure tanks that my grandpa used to use… and those who use bladder style pressure tanks.  Guess which ones we install?

…Give up?  Okay, I’ll give you a hint –  It ain’t your grandpa’s tank.

Jokes aside, I don’t actually have any real issues with the old “air-over-water” style galvanized pressure tanks, after all, they have worked well for many people for many years. As you’ll see in this post, they sometimes have a place but I think you’ll quickly see why the bladder tank has slowly been stealing market share from the galvanized tank for the last few decades.

For the purposes of this post, we will be examining the differences between “air-over-water” and “bladder” style tanks – “bladder” and “diaphragm” are used interchangeably nowadays but “diaphragm” style bladder tanks are most common in our area.


Galvanized Tanks


See the source image


First, we must establish that – for the purposes of practical use, water itself can NOT be compressed.  Air however, CAN be compressed.  And, if you’ve read my blog post relating to why tank sizing is important (if not-now would be a good time – then you will understand the need for pressure tanks to begin with.

Galvanized tanks (aka “air-over-water” tanks) are steel pressure vessels commonly used in water well pump systems.  The galvanized tank system has multiple components but is pretty simple when you understand how they work.  As the well pump pushes water into the tank, the air above the water is trapped and will compress as the water fills until the system reaches the cut-out pressure (usually 50 or 60 psi for residential use but can change based on specific applications).  These systems rely on three small mechanical components to work: the air release valve, the snifter (or schrader) valve, and the bleeder valve which comprise the “air volume control system”.


The Air Release Valve

See the source image An air release valve (pictured left) is a simple float operated valve mounted to the side of a galvanized tank.  As the water fills the tank for the first time, the valve will be releasing air and when the water reaches a certain level (usually about halfway up the tank), the water lifts the float and in turn closes the valve so that the water doesn’t squirt out.  The purpose of this component is to release air when the tank has too much air in it.  We will get into some of the causes of too much air later.




Air Volume Control for Deep Wells Product Image Not all air release valves are created equal.  The 2 on the left are the most common in our area.  The top one is the one we use for almost all applications and the one on the bottom is for special applications, namely when the top one won’t fit in the tan

k bung.  The main difference between these 2 is the materials they are made of.  While it may seem better to have a metal arm holding the float rather than “cheap old plastic” but that’s not the case when something is submerged in water all the time.  Many times we have been called out to replace controls and found that the float has rusted off and now resides in the tank, where it will stay forever until, when combined with other problems, it become lodged in your plumbing causing a scenario that difficult to diagnose (We show pressure in the tank but no water!)


It’s worth noting that usually, a pressure gauge will be mounted directly into the air release valve on the side of the tank, as shown on the right.




The Bleeder Valve and the Snifter Valve


Image result for snifter valve

The other components of an air-over-water tank’s “air volume control” system, are the snifter valve and the bleeder valve.  These 2 components work hand in hand (along with the air release valve) to keep the proper amount of air in the tank.  The snifter valve is mounted above ground, usually on a check valve while the bleeder valve is mounted down the well (20-21′ below the well head) on the first joint of drop pipe.  The job of the snifter is to allow air to enter the pipe while the job of the bleeder is to drain all the water from the first piece of drop pipe when the pump turns off.  It has a flap that closes when the pump starts and pushes the column of air in the first pipe up and into the tank, (glug, glug).  The water flowing through the pipe forces the flap closed and the pressure keeps it closed, not allowing water to squirt out into the well.  Then, when the system reaches cut-out pressure, the pump turns off, the flap opens and the water drains out of the first piece of drop pipe again and down into the well.  This allows the pump to push air into the tank at each start of the pump, when the tank gets too much air, the air release valve lest the excess air out.  These components are a leading cause of service calls.  If any one of the 3 components fail, the system will not work properly and things will start to go wrong.  Usually, the tank will “water-log”, meaning it doesn’t contain enough air to maintain an adequate pump cycle.  When this happens the pump will start more and more frequently, until it either trips the overload protection or causes pump failure.

Image result for morrison rubber bleeder

  1. This was some great information! I can see now how pressure tanks are an important component of private wells as they help water from falling below a safe level. We have a well near our home and if it ever needs fixing we will make sure we call a professional!

  2. How do i know if my air volume control is not working.

  3. The principle of air volume control at pressure tank


  5. Absolutely good simple well tank float operation.
    Thank you

  6. I had problems for several years, two wells tied together. one finally blew the galvanized pressure tank off of the supply to the house and bulged the tank out of shape. I began to demolish the tank and remove and reuse the fittings, I discovered the disconnected tank was full 80 gallons and under pressure! I was able to release the pressure, then when I removed the reducer at the bottom of the galvanized tank i discovered a small torpedo shaped red plastic plug stuck in the reducer to the supply to the house, and so it floated around and at anytime would stick and stop the water to the house, then after some fussing with the system, sometimes it work, other times not so much after a while it just became oh. . . well water is off, water is on. . .

  7. How much air should be in a galvanized air-over-water tank with an AVC valve mounted halfway up the height of the tank…given everything is functioning correctly? Is there a way to tell?

    • Feel the tank with your hand, you’ll feel where the water is because it will be cooler. It should be roughly 1/3 air in the top of the tank.

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