A: An expansion tank is a piece of equipment you’re going to use on any pressurized water system. There are two different kinds of expansion tanks.
There’s a pre-charged or diaphragm tank that has an actual bladder made of different materials for different manufacturers inside of it. The tank, when empty, actually has a pre-charge of air—it has pressure on it already.
The other style is a hydro-pneumatic tank which is actually just the tank filling up until the air volume control device tells the air to stop being released and build pressure up.
These are typically used to eliminate the water hammer effect and as a shock absorber for your pump turning on and off. This way it’s not sending a large jolt through your system and piping.
How does an Expansion tank work?
Anytime a water system, either for hydronic heating or normal water supply, heats water it creates pressure. You think of it as a tea kettle. When you heat it, it builds up pressure and that pressure escapes through the release valve causing it to whistle.
Naturally, your heat source, commercial or residential, does not heat water to the point of boiling, so it doesn’t create steam. However, it still expands when water is heated, and this is called thermal expansion. In a closed heating system, the space in the pipes and heater or boiler is limited. So, when the water is occupying more space and has no escape, pressure builds and can cause damage. Typically, the damage occurs at your system’s weakest points and usually results in a busted pipe or a leak.
The way an expansion tank works is basic—it equalizes a pressure system-wide to create a balance. Let’s just look at a diaphragm-based tank since it’s the oldest design. It’s nothing more than a small tank that is separated into two sections by a rubber bladder or diaphragm. One end connects to your heating system pipes and has water inside. The other section is dry and is pressurized with a little over 10 psi of air.
As water heats up and passes through the heating system the pressure increases. As this happens that pressure forces the diaphragm down, compressing the air in the tank. That compression makes more space for the excess water to flow in. This, in turn, relieves pressure on your system, preventing serious damage to the pipes.
When Is An Expansion Tank Needed?
An expansion tank is relatively inexpensive, so it is always a good idea in a closed-loop system. Although you may not see the immediate effects of excess pressure in your system the damage is still done.
You can compare it to high blood pressure—at first, the symptoms may not be seen. However, the long-term effects on your body shorten your life expectancy. The same goes for your heating or water system. Weak points such as fill valves for toilets, solenoid valves in kitchen appliances, and supply lines tend to fail early due to excess pressure. Additionally, your water heater life expectancy can be cut by as much as half with constant pressure build-up.
Let’s say you have quite a bit of excess pressure coming to your home from your municipal water supply. An expansion tank on its own will not be able to correct this. That’s why your system has a PRV or a check valve. However, without an expansion tank that fluctuating pressure would wreak havoc on your system. The expansion tank prevents that fluctuation, eliminating many system failures. In fact, many cities require new construction homes and businesses to have an expansion tank installed on all closed-loop systems.
Do I Need More Than One Tank?
It’s not so much about quantity as it is having the right size expansion tanks. Even if you have multiple water heaters, you only need the right capacity expansion tank, not multiple. However, you can also choose to add a tank for each heater. But a sufficiently sized single expansion tank would also suffice as long as your building codes allow it.
For a better idea, a 50-gallon heater can easily be handled with a 2-gallon expansion tank. If you have two 50 gallon heaters, you can install one 4-gallon or two of the 2-gallon tanks to accommodate.
If you are unsure what size tank to buy, it’s better to stay on the safe side and go too big rather than too small. An expansion tank that is larger than needed for your system, will still be able to perform just fine. However, a tank that is too small will still allow excess pressure to build—and that is what you’re trying to avoid.
How Long Does An Expansion Tank Last?
This is a question that is hard to give a definitive answer to since so many variables are at play. Variables such as the quality of the tank and the water supply, as well as making sure the tank is properly inflated just to name a few. To err on the side of caution, it is best to not keep using the same tank over a year past the manufacturer’s warranty. Most tanks have anywhere from a one to five-year warranty—stick with ones that offer a longer warranty.
Do They Leak?
As is the case with any part of a plumbing system, expansion tanks can fail over time with continued usage. They go through wear and tear like anything else, and eventually, that wear causes a failure.
Typically, failure occurs in two ways. Either the bladder inside wears out and therefore cannot function, or the connection corrodes and leaks. You can mitigate the chances of this happening by having them properly installed and purchasing high-quality brands such as Goulds.
Water heater expansion tanks need regular maintenance to ensure optimal operation. Most experts recommend that you or a licensed professional perform routine maintenance annually.
Do Expansion Tanks Need Maintenance?
Expansion tanks do experience wear and tear, so they do need to be properly maintained. The internal bladder over time will leak air through diffusion. This can be a leak at a rate of as much as 1 psi per month. Over a single year, that can be detrimental and cause the bladder to not be effective.
If the internal bladder breaks for some reason, the tank won’t fill with water and will not drain correctly. While you can add air to the expansion tank to fix a leak, you cannot repair the internal bladder if it’s ruptured. You must replace the entire tank.
Typically, most reputable brand tanks will last an average of six years with proper maintenance, provided installation was done correctly.
How To Inspect Your Tank
To make sure your tank is in working order you need to know what to look for and inspect your tank frequently:
- Shut off your water supply at the cutoff and open a faucet somewhere on the system to release pressure.
- Remove the cap on the valve stem and connect a tire pressure gauge—you should get a reading of over 75 psi.
- If there’s no pressure at all—your tank has failed and cannot be repaired.
- If there is some pressure inside the tank, the next step is to check the water pressure.
- The tank pressure and water pressure should be within close range of each other. If not, you’ll need to use a bike or hand pump to add more air to the tank. DO NOT use an air compressor—it doesn’t take much to accidentally rupture the bladder. An air compressor is far more likely to fill it too quickly and too much.
If You Need Quality Expansion Tanks Call Us
At Gulf Coast Pump & Supply we carry a wide array of reputable brands and different sizes of expansion tanks. Whatever your application is, we have the right tanks for you and can ship out quickly. Just contact us and one of our technicians will get you started on your order.