How to Find & Use the Air Inlet Valve for Putting Air into a Water Pressure Tank
WATER TANK AIR INLET VALVE - Water Tank Air Valves or Schrader Valves for Adding Water to the Pressure Tank, how to find and use the air valve. How to fix or replace a leaky water tank air valve or Schrader valve or "tire valve". How to use the air inlet valve on a water tank to adjust the air pressure, a step in curing water well pump short-cycling. Definition of Schrader Valves & Dill Valves.
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This article describes the location, use and repair of water tank air valves or schrader valves for adding air to the water pressure tank - the water tank air inlet valve. It's no coincidence that on many water pressure tanks you'll see what looks just like a tire valve (the black capped device at the red arrow in our photo just above).
This air valve provides an easy way to adjust the air charge in water pressure tanks.
Captive air water tanks that use an internal bladder to keep water and air separate, such as the Well-X-Trol™ water
pressure tank, will display an air valve, usually on top of the water tank, and often red in color such as shown
in this photograph.
Older steel water tanks and even some modern bladder type tanks also may include an air input valve or "schrader valve"
to permit air to be pumped into the tank, but it may be located in various locations.
In these installations the air valve may be located anywhere on or near the water tank such that air pumped into the
valve will flow into the water tank itself.
You should not normally need to use the air valve on a water tank with an internal bladder, other than possibly an adjustment at initial installation. Even then, usually the factory air charge is the correct one for most well pump systems.
To use the water tank air valve to put air into a water pressure tank that does not use an internal bladder, see
Step by step details on using the air inlet valve to add air to a bladderless (non-bladder type) water pressure tank are at WATER TANK AIR ADD AT AIR VALVE
But logically you'd expect to see such a valve (if it's present at all)
in a location where air inserted into the valve (say from a tire pump or from a can of compressed air) will flow into the water tank and not just out into the building water supply piping or water pump.
Here is a close up view of the typical air valve or schrader valve located on the top of a bladder type captive air
water tank. These tanks come from the factory with air pre-charged and you do not normally need to change the air volume or
pressure in these tanks.
Notice that the warning label surrounding this air valve indicates that "WARNING! Removal of cap by persons other than authorized dealer may void warranty". This is because the
manufacturer is not going to accept responsibility if you over pressurized the tanks's internal system and cause damage.
Furthermore, over pressurizing any tank of any type beyond its working pressure is very dangerous and can cause the
tank to rupture or explode. That's why we require a pressure relief valve on any pressurized tank, even a water tank.
Guide to Repairing Leaky Water Tank Air Valves
Sometimes when we remove the cap from a water tank air valve, or more likely when we try pumping air into the water tank at the water tank's air valve, we're troubled by water (or air) leaking back out at us from the valve - making us sorry we touched it in the first place.
If the air valve or "tire valve" or Schrader valve on your water tank is leaking water or air there are a few wonderfully easy steps you can take. We describe how to clean an air valve to get it to stop leaking, a simple emergency way to stop a leaky air valve on a water tank, and how to replace the valve stem core if that's needed.
Definition: Schrader valves (American Valves) and Dill Valves are used prinicipally on vehicle tires to insert (or release) air to a specified pressure. 
Schrader or Dill valves are also used, often in modified form with an internal spring with strength matched to the application where air inlet or outlet or water or air pressure management require adjustment on water pressure tanks and similar systems.
The Schrader valve or Dill valve (two different companies) consists of an externally and internally threaded metal stem.
The external valve base and stem connect (using appropriate seals or washers) to the vehicle wheel rim, or in plumbing to a water pressure tank or water piping at an appropriate location.
The internal stem of the valve accepts a replacable part, the actual control valve that opens (when a center pin is pressed) to admit air or to release air.
In reverse, pressure inside the system pushing against the valve stem core closes the valve when its center pin is not depressed. 
Similar control valves but of different diameters are used in other countries than those comprising North America.
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