A water hammer arrestor works by absorbing the shockwave created when water flow abruptly stops, preventing damage to your plumbing system. It acts as a hydraulic shock absorber, much like the shock absorbers on a car smooth out bumps in the road. This device is a crucial component for water hammer prevention, ensuring the longevity and quiet operation of your pipes.
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Deciphering the Force of Water Hammer
Water hammer, also known as a pipe hammer dampener effect or plumbing shock eliminator, is a phenomenon that occurs in plumbing systems when the flow of water is suddenly stopped or changed rapidly. Imagine a train moving at high speed; if it suddenly brakes, the momentum of the entire train has nowhere to go, and it creates a powerful jolt. In plumbing, this jolt is caused by the kinetic energy of the moving water.
When a valve, such as a faucet or a washing machine solenoid valve, closes quickly, the water immediately behind it is forced to a standstill. However, the water further back in the pipe is still in motion. This moving water slams into the stopped water, creating a pressure wave that travels back through the pipe at the speed of sound in water. This wave bounces off fittings, bends, and the end of the pipe, reverberating back and forth, causing the characteristic banging or hammering sound and significant stress on the pipework.
The effects of water hammer can range from annoying noises to severe damage, including:
- Pipe Rattling and Banging: The most common and immediate sign.
- Loose Fittings and Leaks: Repeated shocks can loosen pipe connections, leading to drips.
- Damage to Valves and Appliances: Solenoid valves in washing machines, dishwashers, and ice makers are particularly vulnerable.
- Cracked Pipes: In severe cases, the pressure surges can cause pipes to split or burst.
- Damage to Pressure Gauges and Water Meters: Sensitive components can be compromised.
Fathoming the Function of a Water Hammer Arrestor
A water hammer arrestor is specifically designed to mitigate these destructive pressure surges. It acts as a plumbing surge suppressor, effectively dissipating the energy of the moving water before it can cause damage. The core principle behind its operation is to provide a cushion or an expandable space within the plumbing line that can absorb the shockwave.
There are several types of water hammer arrestors, but they all operate on similar principles, utilizing either trapped air or a flexible barrier to absorb the pressure. The most common types include the air chamber principle and the diaphragm arrestor function, along with variations like the piston arrestor mechanism.
The Air Chamber Principle: A Simple Solution
The earliest and simplest form of a water hammer arrestor relies on the compressibility of air. This is often referred to as a simple air chamber or a standpipe arrester.
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How it Works: An air chamber is essentially a vertical section of pipe installed above the water line, typically at a fixture. When the system is first filled, air gets trapped in this chamber. When a valve closes abruptly, the pressure wave travels towards the arrestor. As the wave enters the chamber, it compresses the trapped air. Air is much more compressible than water, so the air cushion absorbs a significant portion of the shock’s energy, preventing it from propagating further through the system and causing damage. The water then recedes slightly into the chamber, and the air expands back to its original volume, pushing the water back into the pipe.
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Advantages:
- Simple to install.
- No moving parts.
- Cost-effective.
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Disadvantages:
- Over time, the air in the chamber can be absorbed by the water (a process called “air entrainment” or “air logging”). This reduces the effectiveness of the arrestor, and the chamber can become waterlogged, rendering it useless.
- When air logging occurs, the chamber fills with water, and the system loses its cushioning effect, leading to a recurrence of water hammer.
- May require periodic “recharging” by draining the water system to allow air back into the chamber.
The Diaphragm Arrestor Function: A More Advanced Design
Modern water hammer arrestors often utilize a diaphragm or a bladder to separate the water from a captive air or gas charge. These are generally more reliable and long-lasting than simple air chambers.
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How it Works: A diaphragm arrestor consists of a sealed chamber. Inside this chamber, there is a flexible diaphragm (often made of rubber or a similar resilient material) that divides the chamber into two sections. One section is connected to the plumbing line and is filled with system water. The other section contains a permanent charge of air or an inert gas, like nitrogen. When a pressure surge occurs, the incoming water pushes against the diaphragm. The diaphragm flexes into the gas-filled chamber, compressing the gas. This compression absorbs the shockwave, similar to the air chamber principle but with the added benefit of the diaphragm preventing the air from being absorbed by the water. The diaphragm acts as a barrier, maintaining the separation and effectiveness of the air cushion.
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Advantages:
- Longer lifespan and consistent performance.
- Prevents air absorption and waterlogging.
- Effective over a wider range of pressures.
- Typically more compact than air chambers.
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Disadvantages:
- More complex and potentially more expensive than simple air chambers.
- The diaphragm can eventually degrade and fail, though this is usually after many years of service.
The Piston Arrestor Mechanism: Robust Shock Absorption
Another effective type of arrestor employs a piston mechanism. This design is known for its durability and ability to handle higher pressure surges.
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How it Works: A piston arrestor mechanism features a piston that moves freely within a cylinder. This cylinder is connected to the plumbing line. The piston is typically spring-loaded or has a captive air charge behind it. When a water hammer event occurs, the surge of water pushes the piston. The piston moves within the cylinder, compressing the spring or the air charge behind it. This movement absorbs the kinetic energy of the water. As the pressure wave subsides, the spring (or compressed air) pushes the piston back to its original position, restoring the arrestor. The key here is that the piston creates a seal, preventing water from coming into direct contact with the air charge, thus avoiding the waterlogging issue common with simple air chambers.
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Advantages:
- Very durable and robust.
- Excellent at handling high-velocity water flow and significant pressure spikes.
- Long service life.
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Disadvantages:
- Can be more expensive than diaphragm or air chamber types.
- The piston and cylinder can wear over time, though this is usually a slow process.
Factors Influencing Water Hammer and Arrestor Effectiveness
Several factors contribute to the severity of water hammer and influence how well an arrestor performs its water hammer solution role:
- Valve Closure Speed: The faster a valve closes, the more abrupt the change in water flow, and thus, the greater the pressure surge. Solenoid valves in appliances are notorious for their rapid closure.
- Water Velocity: Higher water velocities mean greater kinetic energy, leading to more severe water hammer effects. This is influenced by pipe diameter, water pressure, and flow rate.
- Pipe Length and Configuration: Longer runs of pipe can allow water to accelerate to higher velocities. Elbows and changes in pipe direction can also contribute to turbulence and increase the likelihood of water hammer.
- Pipe Material and Support: Rigid pipes are more prone to transmitting shockwaves and noise. Poorly secured pipes can rattle and bang against structures, amplifying the sound and stressing connections.
- System Pressure: Higher system pressures generally result in more forceful water hammer events.
Where and How to Install Water Hammer Arrestors
Proper installation is crucial for the effective operation of any water hammer arrestor. They are typically installed at or near the source of the problem, which is usually close to quick-closing valves.
Common Installation Locations:
- Washing Machines: Install directly on the supply lines leading to the hot and cold water inlets of the washing machine. This is a very common location due to the rapid solenoid valve closure.
- Dishwashers: Similar to washing machines, install on the hot water supply line.
- Ice Makers/Refrigerators: If the ice maker has a solenoid valve, an arrestor can be beneficial.
- Single-Lever Faucets: Especially those with ceramic disc cartridges that can close quickly.
- Toilet Fill Valves: Some modern toilet fill valves can also cause minor shockwaves.
- Sprinkler Systems: Quick-closing valves in irrigation systems can create significant water hammer.
Installation Steps (General Guide – Always Consult Manufacturer Instructions):
- Turn Off Water Supply: Locate the main water shut-off valve for your home and turn it off. Open a nearby faucet to drain the remaining water from the system.
- Identify Installation Point: Choose a location as close as possible to the appliance or fixture causing the water hammer.
- Install the Arrestor:
- Threaded Arrestors: These typically screw directly onto existing threaded pipe fittings or hose bibs. You might need a small extension nipple or a tee fitting to accommodate the arrestor without interfering with other connections.
- Compression or Sweat Fittings: For more permanent installations, arrestors with compression or sweat fittings can be integrated directly into the pipe run.
- Ensure Correct Orientation: Most arrestors are designed to be installed in a specific orientation (often vertical), especially air chamber types to ensure air is trapped at the top. Diaphragm and piston types may be more forgiving, but it’s always best to follow manufacturer guidelines.
- Turn Water Supply Back On: Slowly turn the main water supply back on. Check for any leaks around the installation point.
- Test the System: Open and close the relevant faucet or appliance to simulate the condition that causes water hammer and listen for any banging sounds. The arrestor should have significantly reduced or eliminated the noise.
Maintaining the Pressure Surge Control
While modern arrestors, particularly diaphragm and piston types, are designed for minimal maintenance, simple air chambers require periodic attention.
- Air Chambers: If you notice water hammer returning, your air chamber may be waterlogged. The solution is to turn off the water supply, drain the system, and then reopen the shut-off valve to allow air to refill the chamber. This is a temporary fix, and a more permanent solution like a diaphragm or piston arrestor might be necessary.
- Diaphragm/Piston Arrestors: These are generally maintenance-free. If water hammer returns, it might indicate a faulty arrestor that needs replacement.
Types of Water Hammer Arrestors: A Comparative Table
Here’s a look at the common types of arrestors and their characteristics:
| Feature | Simple Air Chamber | Diaphragm Arrestor | Piston Arrestor Mechanism |
|---|---|---|---|
| Working Principle | Compressed trapped air | Compressed gas separated by diaphragm | Compressed spring or gas via piston |
| Air Retention | Prone to waterlogging | Excellent | Excellent |
| Lifespan | Shorter; may need re-charging | Long | Very Long |
| Effectiveness | Good when properly charged; decreases | Consistently high | Consistently high |
| Maintenance | Periodic draining/re-charging | Minimal to none | Minimal to none |
| Complexity | Simple | Moderate | Moderate to High |
| Cost | Low | Moderate | Moderate to High |
| Installation | Often vertical | Can be installed in various orientations | Can be installed in various orientations |
Conclusion: A Vital Component for a Quieter, Safer Plumbing System
Water hammer is not just an annoyance; it’s a destructive force that can silently degrade your plumbing system. A water hammer arrestor, whether employing the air chamber principle, a diaphragm arrestor function, or a piston arrestor mechanism, is an essential water hammer solution for any household experiencing these shockwaves. By acting as a hydraulic shock absorber and plumbing surge suppressor, these devices protect your pipes, fittings, and appliances, ensuring a quieter, more reliable, and safer plumbing environment. Investing in quality water hammer prevention through the installation of these plumbing shock eliminators is a wise choice for any homeowner.
Frequently Asked Questions (FAQ)
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What causes the banging in my pipes?
The banging is usually caused by water hammer, which occurs when water flow is stopped suddenly by a valve. The momentum of the moving water creates a shockwave that travels through the pipes, causing them to vibrate and make noise. -
Are water hammer arrestors necessary in all homes?
Not necessarily in all homes, but they are highly recommended if you experience the banging sound of water hammer. They are particularly important in homes with quick-closing valves (like those in washing machines and dishwashers) or where pipework is older or less robust. -
Can I install a water hammer arrestor myself?
Yes, for many types of arrestors, particularly those with threaded fittings, DIY installation is feasible. However, always ensure you turn off the main water supply, follow the manufacturer’s instructions carefully, and check for leaks after installation. If you are unsure, it’s best to call a qualified plumber. -
How many water hammer arrestors do I need?
The number of arrestors needed depends on the number of fixtures or appliances that cause water hammer. Typically, an arrestor should be installed at or near each appliance with a quick-closing valve. Some plumbers recommend a general arrestor on the main line for overall pressure surge control, but specific appliance locations are the priority. -
How long do water hammer arrestors last?
Simple air chambers may need servicing or replacement every few years as the air gets absorbed. Modern diaphragm and piston arrestors, however, can last for 10 to 20 years or even longer with proper installation and no unusual system stresses. -
Will a water hammer arrestor stop all pipe noise?
Water hammer arrestors are designed to stop noise specifically caused by pressure surges. Other pipe noises, such as expansion and contraction due to temperature changes or loose pipe supports, may require different solutions.