Water Hammer: It's Causes & Solutions To The Problem

What is Water Hammer?

Water is a phenomenon that can occur in any piping system where valves are used to control the flow of media. When valves close or an acting pump stops suddenly, the momentum of the water can create a pressure wave. This wave rebounds from the closed port, travelling back up the pipe. This phenomenon is exacerbated when the frequency of the transient pulse resonates with the pipework or from standing waves already present in the system, which can build to the extend where severe damage can be caused. 

Causes of Water Hammer

Many of us have experienced banging pipes when a tap is turned off. In fact, that's likely why you're reading this guide right now! Water hammer has a number of potential causes, all of which have been detailed below. 

Loose pipes

If pipes are not secured correctly, or perhaps have become unsecured completely, shock waves within the pipework are likely to be exacerbated by the physical banging of the pipe itself. Pipes should be fixed securely to sturdy materials, to ensure their rigidity for years to come. Make sure to check under floorboards and in cupboards. Thought these pipes may be out of sight, they still require attention! 

Worn stop valves

Stop valves, commonly referred to as stopcocks, can cause water hammer if their gland packing is lose and/or they have worn washers. Stop valves will almost always be open at the time of water hammer, meaning it's shock waves have the ability to knock the valve handle and valve jumper. 

Entrapped air

Water hammer can commonly be caused by trapped air inside the system. Air can find its way into your pipework system if empty pipework is filled too quickly. To minimise the risk of air accumulating with the system, ensure pipework is filled slowly to allow air to escape. 

Alternatively, air-relief valves can be used to allow entrapped air to escape. These valves are placed at high points within the system. 

Ball-float valves

Water hammer can result from ripples inside an open water tank where a ball/float valve is used to control the inflow/outflow of water. As water flows into the sealed tank, the valve float can rock up and down, which opens and closes the valve. This movement can create a pressure wave which resonates through the pipework, creating the hammer sound. As plastic tanks flex considerably more, metal plates can be utilized to add rigidity to their structure to weaken this effect. 

Fast acting valves

Another common cause of water hammer is fast-acting valves. Fact-acting valves, such as electronically operated solenoid valves, stop water instantaneously , resulting in water shock waves reverberating back up the pipework. 

The Effects of Water Hammer

Whilst it may look and sound harmless, ignoring water hammer can ultimately result in severe damage to your pipework system. The long-term effects of water hammer might present themselves in the following ways:

• Leaks: Water hammer has the potential to damage joints, fittings and connections, resulting in poor seals and ultimately leaky pipes. 
• Ruptured pipes: Ruptured pipes due to built-up pressure can be particularly expensive to repair. Due to the nature of the repair, it will often entail a major replacement operation. 
• Property damage: If leaks go unnoticed, they have the potential to damage surrounding electrical equipment and/or lead to the corrosion of infrastructure. Think of electrical cabling and the rotting of supporting beams and/or foundation. 
• Downtime: If extensive damage is caused to a system, the financial cost of downtime to the system or building entirely (if commercial) needs to be considered. 

How to Stop/Prevent Water Hammer

Secure & wrap loose pipes

Check that all pipes are suitably secured to their surroundings using strong and sturdy fixings. Pipe straps can be added to provide additional support, though careful consideration should be taken when choosing their material. Some metals can chemically react with one another and corrode, leading to poor fitment down the line. Some others, if heat is involved, may expand at different rates, resulting in poor fitment. 

Pipes can also be wrapped in foam insulation to absorb the inner shock waves. 

Install air-relief valves

Air-relief valves, placed at high points throughout a pipework system, allow entrapped air to escape. In scenarios where a system is spread across a large flat area, air-relief valves should be placed early in the system, middle of the system, around pumps and downstream. 

Install air chambers

Air chambers are also an effective solution to water hammer. These systems consist of a short segment of pipe with an empty/air filled chamber that cushions shock waves. This reduces the size of the shock waves downstream of the valve. It's worth noting, however, that these air chambers need to be drained of water every few months, to ensure their continued effective operation. 

Install water hammer arrestors

Water hammer arrestors operate similarly to air chambers. However, instead of a vertical pipe that absorbs pressure, water hammer arrestors use a mixture of springs and air bladders to absorb water movement and reduce shock waves downstream of quick closing valves. Whilst more expensive, water arrestors don't require any ongoing maintenance (unlike air chambers), so are an effective long-term solution to water hammer. 

Our range of water hammer arrestors

At Measure Monitor Control, we stock a variety of water hammer arrestors.