Water hammer arrestors are an important part of any plumbing system. They help prevent damage from water hammer, which is the loud banging noise that can happen when a valve is closed suddenly. The sudden stop in water flow creates a pressure wave that travels quickly back through the pipes, causing vibrations and stress on pipe joints and fittings. Water hammer arrestors absorb these pressure waves to protect the plumbing system.
What is a water hammer arrestor?
A water hammer arrestor is a device that contains air to absorb water hammer shock waves. It has a body, gaskets, and air chamber. When installed properly on a water supply line, the water hammer arrestor will absorb the shock wave when nearby valves are closed suddenly, preventing the wave from continuing down the pipe. This stops the banging noises and damage from water hammer.
There are two main types of water hammer arrestors:
- Piston type – These have an internal piston that moves up and down to absorb the shock wave.
- Diaphragm type – These use a flexible diaphragm that flexes to absorb the pressure wave.
Water hammer arrestors are placed near points where water hammer occurs, such as near washing machines, dish washers, valves, and quick-acting solenoid valves. They may be installed in any water distribution system that uses quick-acting valves. Proper installation is key for the water hammer arrestor to work effectively.
Where should water hammer arrestors be installed in a home?
In a home plumbing system, there are several locations where water hammer arrestors are commonly installed:
- Washing machine water supply lines – Water hammer from the washing machine valves turning on and off is a common source of water hammer noise and pipe stress. Installing a water hammer arrestor on the hot and cold water lines just before they reach the washing machine will help absorb these shocks.
- Dishwasher water supply line – Like washing machines, dishwashers also cause water hammer from the valve opening and closing during operation. Put a water hammer arrestor right before the dishwasher on the supply line.
- Kitchen sink supply lines – The kitchen is where quick-closing faucets and sprayers are often used, which can lead to water hammer. Install arrestors on the supply lines, such as under the sink.
- Bathroom sink supply lines – Bathroom faucets and showers are also common sources of water hammer. Place arrestors on the supply lines serving these fixtures.
- Toilet supply line – The rapid closing of toilet fill valves can cause water hammer. Install an arrestor on the toilet supply line, such as near the shutoff valve.
- Sprinkler system supply line – Sprinkler valves turning on and off rapidly during operation is a prime source of water hammer. Install an arrestor near the sprinkler valves.
By installing water hammer arrestors at these locations, you can absorb pressure shock waves before they cause damage. Follow the manufacturer’s recommendations for proper installation.
Where should they be installed in commercial and industrial facilities?
In commercial and industrial plumbing systems, proper placement of water hammer arrestors is also important to protect pipes from damage. Some key locations include:
- Behind automatic washer valves – Commercial washing machines in laundromats, hospitals, fire stations, etc. require water hammer arrestors.
- Commercial dishwasher supply lines – Large dishwashers in restaurants, cafeterias and bars should have arrestors installed.
- Steam boiler lines – Steam valves on boilers will cause water hammer, so install arrestors on boiler supply lines.
- Pump discharge and suction lines – Centrifugal pump outlets and inlets are common water hammer locations. Install arrestors here.
- Solenoid valves – Rapid opening and closing of solenoid valves warrant water hammer arrestors nearby.
- Air conditioning cooling lines – Valves controlling chiller flows can induce water hammer in AC systems.
Proper placement near quick-closing valves and equipment subject to water hammer is key. Follow manufacturer guidelines for installation. Arrestors may also be placed every 200 feet in long pipe runs.
What size water hammer arrestor should be used?
Choosing the right size water hammer arrestor for a particular location depends on several factors:
- Pipe size – Match arrestor size to pipe size. For example, use 1/2″ arrestors on 1/2″ pipes.
- Flow rate – Higher flow applications need larger arrestors that can absorb more shock.
- Type of fixtures – Arrestors for fixtures like washing machines should match the machine’s water supply needs.
- Length of run – Longer pipe runs may need multiple arrestors spaced throughout.
Manufacturers provide sizing guides to select the optimal water hammer arrestor depending on these factors. For example, a 1/2″ diaphragm-type arrestor would be appropriately sized for a bathroom vanity faucet line. A 3/4″ piston-type unit would better suit a washing machine. Follow manufacturer instructions carefully.
How do you install a water hammer arrestor properly?
Proper installation is essential for a water hammer arrestor to work effectively. Here are some key installation tips:
- Position vertically – Install the arrestor in an upright and vertical position. Horizontal installation can reduce effectiveness.
- Directional flow – Make sure flow moves through the arrestor in the proper direction marked on the device.
- Accessible location – Install in an accessible area for any needed maintenance or repairs down the road.
- Secure fittings – Use the proper size fittings and ensure they are installed securely with no leakage.
- Support – Use hangers or braces to provide adequate support and prevent strain on the pipes.
- Single branch line – Install on a single branch line near the valve rather than on mains or multi-branch manifolds.
- Multi-story buildings – Use arrestors on the top and bottom floors, since pressure differentials between floors can contribute to water hammer.
Following the manufacturer’s instructions for proper installation, positioning, and support is highly recommended to maximize the benefits of the water hammer arrestor.
Where should water hammer arrestors NOT be installed?
While water hammer arrestors are very helpful in reducing water hammer damage, there are a few places they should not be installed:
- Gas lines – Never install water hammer arrestors on gas supply lines. They are only intended for water plumbing.
- Main water service entry – Arrestors are not needed at the main water line entering the building.
- Hose bibbs – Outdoor hose connections do not require water hammer arrestors.
- Overflow lines – Arrestors should not be placed on overflow pipes.
- Sprinkler main lines – Use only on branch lines near valves, not the main sprinkler supply line.
- Tankless water heaters – The flow sensors on tankless heaters can be affected by arrestors.
Improper placement can reduce the effectiveness of water hammer arrestors. Follow manufacturer guidelines and local plumbing codes for where not to install them.
Signs you need water hammer arrestors
Here are some signs that may indicate you need to install water hammer arrestors in your plumbing system:
- Loud banging noises – If you hear loud clanging or hammering sounds when water is turned off suddenly, you likely need arrestors.
- Piping vibrations – Tactile vibrations in pipes when water is turned off quickly points to water hammer.
- Fixture shaking – Water hammer can cause fixtures like sinks or laundry machines to shake visibly.
- Leakage – Water hammer stresses pipe joints, and leaks may occur as seals fail.
- Pressure relief valve discharge – Chronic water discharge from a pressure relief valve after the water is turned off can indicate water hammer.
- Valve malfunction – Water hammer can impede proper valve operation over time.
If you notice any signs of water hammer, the best solution is to strategically install water hammer arrestors based on the sources and locations of the pressure shocks.
Conclusion
Installing water hammer arrestors at key locations is an effective way to prevent the damaging effects of water hammer. For residential plumbing systems, be sure to place arrestors on laundry, kitchen, and bathroom supply lines prone to quick valve closures. Commercial systems will benefit from arrestors near equipment like automatic washers, dishwashers, boilers, and solenoid valves. Proper sizing based on pipe diameter and flow rate is important. Follow manufacturer guidelines for installation to ensure the water hammer arrestors work optimally. Position them vertically in accessible areas on single branch lines. Water hammer arrestors are a simple solution to extend the life of your pipes and plumbing fixtures by absorbing hydraulic pressure shock.