A bladder pressure tank contains pressurized air and water separated by a flexible membrane (bladder). These tanks are typically precharged with air at the factory.
As water pressure changes, the volume of air in a bladder tank contracts and expands. Periodically, the amount of air in the tank should be measured and the tank recharged if the air is too low.
Although a bladder tank for a typical home or smaller commercial water system will not have a very large storage capacity, it will perform several important functions:
- It maintains a desired range of water pressure in the distribution system.
- It minimizes pump cycling, preventing frequent starts and stops and protecting pumps from motor burnout or other water system components from damage.
- It protects against water hammer.
If it appears that a bladder tank is not operating correctly, check the tank’s air charge:
- Disconnect electrical power to the pump.
- Drain the tank by opening the closest faucet.
- Check the tank’s pressure by placing an air pressure gauge on the air charging valve on the top of the tank.
- Add air if the pressure is more than 2 psi below the pump cut-in pressure. Use caution when using an air compressor or air pump.
- Release air if the pressure is 2 psi above the pump cut-in pressure (lowest pressure in the operating range).
- Check for leaks in the air charging system by dripping a soap solution on the air charging valve.
- Restart the pump and run through a normal cycle to verify the setting. If tank pressure drops abnormally, the bladder inside the tank may have a tear or hole in it.
Is it waterlogged?
You should also check a bladder tank to determine if it’s waterlogged. A tank is waterlogged if it is completely filled with water or has too much water to function correctly. Waterlogged bladder pressure tanks contribute to the following problems:
- The pump motor cycles too often. Frequent cycling can shorten the lifespan of a pump.
- Because waterlogged tanks can contain stagnant water, there can be unsatisfactory coliform samples or taste and odor complaints.
- Premature tank failure: the inside walls of a waterlogged tank can corrode and weaken from the exposure to water.
It may often be most cost-efficient for the customer to simply replace a waterlogged tank.
Reasons for waterlogging
Bladder tanks can become waterlogged for many reasons. Some of the more common reasons are:
- Sediment, such as iron and manganese, can coat the surface of the bladder, causing it to harden and become less flexible.
- Sediments can plug the fill or draw line, preventing the tank from filling and emptying normally.
- Excessive levels of chorine can damage the bladder, causing it to become brittle and less flexible.
- Tanks sitting directly on the ground or on another surface that is continually moist can rust and lose structural integrity.
- Chlorinators can give off corrosive vapors that cause the tank to rust.
When working with bladder pressure tanks, always be sure to read and follow the manufacturer’s safety warnings.
The above article was adapted from an April 2006 article available from the Washington State Department of Health, Division of Environmental Health, Office of Drinking Water, which can be accessed at: www.doh.wa.gov/ehp/dw.