How Do Water Hammer Arrestors Work

Sudden banging noises in your plumbing when you turn off a faucet or when your washing machine shuts off? That's likely water hammer, and it's more than just an annoying sound. It’s a powerful force that can damage your pipes, weaken joints, and even lead to leaks. The solution? Water hammer arrestors. This guide explains how these simple devices work, why you need them, and how to choose the right ones for your home's HVAC and plumbing systems.

Understanding Water Hammer

Water hammer, also known as hydraulic shock, occurs when flowing water is suddenly stopped or changes direction. Imagine a train traveling at full speed abruptly slamming on its brakes. The force of the water crashing against the closed valve creates a pressure surge that reverberates through your pipes. This surge is what causes the banging noise. Over time, these repeated shocks can weaken your plumbing system.

The Physics Behind the Bang

When a valve closes quickly, the kinetic energy of the moving water is converted into pressure energy. This pressure wave travels back through the pipes at the speed of sound in water (around 4,800 feet per second!). When it hits a bend or a closed valve, it creates a shock wave. The intensity of the water hammer depends on several factors, including:

Water Velocity: The faster the water is flowing, the stronger the water hammer effect.
Pipe Length: Longer pipe runs have more water mass in motion, leading to a more significant surge.
Valve Closure Speed: Quick-closing valves (like those in washing machines and dishwashers) are notorious for causing water hammer.
Pipe Material: Rigid pipes like copper and steel transmit the shock more effectively than flexible pipes like PEX.

What are Water Hammer Arrestors?

Water hammer arrestors are devices designed to absorb the shock of water hammer. They act like miniature shock absorbers for your plumbing system, providing a cushion of air or a spring-loaded piston to dissipate the energy of the pressure surge.

How They Work: Two Main Types

There are two primary types of water hammer arrestors:

Air Chamber Arrestors

These are the simplest type. They consist of a vertical pipe (or chamber) filled with air. When a pressure surge occurs, the air compresses, absorbing the shock. However, over time, the air can become absorbed by the water, rendering the arrestor ineffective. This is a common problem with older, DIY air chambers that homeowners might have installed years ago. These older designs required periodic draining to replenish the air cushion.

Pros: Simple design, relatively inexpensive.

Cons: Can lose air charge over time, require periodic maintenance (draining).

Mechanical Arrestors

These are more sophisticated and reliable. They use a sealed chamber containing a piston or diaphragm pre-charged with air or nitrogen. When a pressure surge occurs, the piston or diaphragm moves against the air or nitrogen, absorbing the shock. Because the air or nitrogen is sealed, these arrestors typically don't lose their charge and require less maintenance.

Pros: More reliable, less maintenance, longer lifespan.

Cons: More expensive than air chamber arrestors.

Why You Need Water Hammer Arrestors

The benefits of installing water hammer arrestors extend beyond simply eliminating annoying noises. Here's why they are a crucial investment for your home:

Protect Your Pipes: By absorbing the shock of water hammer, arrestors prevent stress on your pipes and joints, extending their lifespan and reducing the risk of leaks.
Prevent Damage to Appliances: Water hammer can damage the solenoid valves in appliances like washing machines, dishwashers, and ice makers. Arrestors protect these sensitive components.
Reduce Noise: Eliminate the annoying banging and clanging that can disrupt your peace and quiet.
Save Money: By preventing leaks and appliance damage, arrestors can save you money on repairs and replacements in the long run.

Choosing the Right Water Hammer Arrestors

Selecting the appropriate water hammer arrestors is essential for optimal performance. Consider these factors:

Size

Arrestors are sized based on the diameter of the pipe they will be connected to. Common sizes include 1/2 inch, 3/4 inch, and 1 inch. Consult with a plumber or refer to the manufacturer's sizing chart to determine the correct size for your plumbing system. The size is directly related to the flow and water pressure in your system. Too small and it is ineffective. Too large and it can impact water pressure.

Type

For most residential applications, mechanical arrestors are the preferred choice due to their reliability and low maintenance requirements. Air chamber arrestors may be suitable for less demanding applications, but be prepared to maintain them regularly.

Location

Install arrestors as close as possible to the source of the water hammer. This typically means near quick-closing valves in appliances like washing machines, dishwashers, and toilets. You may also need to install arrestors on long pipe runs or near fixtures that are prone to causing water hammer.

Quality and Certification

Choose arrestors from reputable manufacturers that are certified to meet industry standards. Look for certifications from organizations like ASSE (American Society of Sanitary Engineering) and IAPMO (International Association of Plumbing and Mechanical Officials). These certifications ensure that the arrestors have been tested and meet performance and safety requirements.

Installation

While some homeowners may be comfortable installing water hammer arrestors themselves, it's generally recommended to hire a qualified plumber. Proper installation is crucial for the arrestors to function effectively and prevent leaks. A plumber can also assess your plumbing system and recommend the best locations for installing arrestors.

Maintenance

Mechanical arrestors typically require very little maintenance. However, it's a good idea to periodically inspect them for leaks or damage. If you have air chamber arrestors, you will need to drain them periodically to remove any accumulated water and restore the air cushion. Consult the manufacturer's instructions for specific maintenance recommendations.

Popular Brands and Models

Here are a few reputable brands and models of water hammer arrestors to consider:

Sioux Chief: Offers a range of mechanical arrestors suitable for various applications. Known for their durability and reliability.
Oatey: Provides both air chamber and mechanical arrestors at competitive prices.
Watts: Specializes in high-quality plumbing and HVAC products, including water hammer arrestors.
Zurn: Offers a variety of commercial-grade and residential water hammer arrestors designed for optimal performance.

When comparing models, look for features like:

Maximum operating pressure: Ensure it matches your water pressure.
Temperature rating: Suitable for your water temperature.
Connection type: Compatible with your plumbing system (e.g., threaded, sweat).
Material: Brass or stainless steel for durability.

Cost

The cost of water hammer arrestors varies depending on the type, size, and brand. Air chamber arrestors typically cost between $10 and $20, while mechanical arrestors range from $20 to $50 or more. Installation costs will depend on the complexity of the job and the plumber's hourly rate.

Water Hammer and HVAC Systems

While primarily associated with plumbing, water hammer can also impact HVAC systems, particularly those that utilize water for heating or cooling. For instance, chilled water systems in commercial buildings are susceptible to water hammer if valves close rapidly. In residential settings, improperly installed or maintained zone valves in hydronic heating systems can also contribute to the problem.

When evaluating or upgrading your HVAC system, especially if it involves water-based heating or cooling, consider the potential for water hammer and ensure that appropriate arrestors are installed to protect the system's components.

Conclusion

Water hammer arrestors are a simple yet effective solution to a common plumbing problem. By understanding how they work and choosing the right ones for your home, you can protect your pipes, prevent appliance damage, and enjoy a quieter, more peaceful living environment. Investing in water hammer arrestors is a small price to pay for the long-term benefits they provide.