What Is Water Hammer in Pump Systems? Causes, Symptoms and Prevention

What Causes Water Hammer?

Understanding what causes water hammer is essential because the root cause is often linked to a combination of pump operation, valve performance, pipework design and pressure control.

Common causes of water hammer include:

• Rapid valve or tap closure
• Pumps starting or stopping suddenly
• Power failure
• Incorrect pipe sizing
• Poor non-return valve performance
• Air trapped in pipework
• Sudden directional flow changes
• Incorrectly sized or poorly maintained pressure vessels
• Poor pump sequencing or control settings

One of the most common water hammer causes in booster sets is a sudden stop/start event. When a pump starts or stops too aggressively, the water inside the pipework reacts instantly. This can create a pressure surge that travels through the system and results in banging, knocking or vibration.

Non-return valves can also be a major water hammer cause. If a valve closes too slowly or slams shut after reverse flow has already started, it can create a sharp pressure shock. Likewise, if the pressure vessel is undersized, incorrectly pre-charged or not functioning properly, the system may not have enough capacity to absorb pressure fluctuations.

What Does Water Hammer Sound Like?

The sound of water hammer is commonly described as a loud bang, knock or hammer noise within the pipework. Many facilities teams first notice a problem when they hear water hammering noise, water banging in pipes or repetitive hammering in pipes during pump operation.

You may notice:

• Water banging in pipes
• A knocking noise when pumps start or stop
• Repetitive hammering in pipes after valve closure
• Water surging and vibration through pipework
• Pipe hammering when demand changes
• Hammer noise near booster sets, valves or risers

In critical systems, water hammering noise may be heard near plant rooms, risers, distribution pipework or pump equipment. However, the source of the noise is not always the source of the problem. A pressure shockwave can travel through the system, meaning the visible or audible symptom may appear some distance away from the root cause.

Why Water Hammer Is a Serious Issue in Critical Pump Systems

For critical sites such as hospitals, universities and prisons, water hammer should never be ignored. It can place significant stress on mechanical and electrical components, particularly in systems where pumps operate frequently or pressure demand changes throughout the day.

At Dura Pump, water hammer is something we consider across a wide range of pump systems, including:

• Booster sets
• Chilled water pumps
• Pressurisation units
• Wastewater pumping stations

In booster sets, water hammer can be especially problematic because these systems are designed to maintain stable pressure across a building. If controls, pressure vessels or non-return valves are not correctly selected or maintained, the booster set may respond too aggressively to pressure changes.

Over time, repeated pressure shock can lead to:

• Burst pipework
• Seal failure
• Valve damage
• Control faults
• Pump wear
• Premature component failure
• Pressure instability
• Increased maintenance costs
• Unplanned downtime

In sensitive environments such as hospitals, universities and prisons, downtime can cause major disruption. That is why it is important to address water hammer at the root cause rather than simply trying to reduce the noise.

Water Hammer in Pumps: Why It Happens

Water hammering in pumps often happens when water flow changes faster than the system can safely absorb. Pump water hammer is particularly common in booster sets, pressurisation systems and pumping stations where pressure demand changes rapidly.

In booster sets, pump water hammer can occur when pumps are brought online or taken offline too quickly. If a pump stops suddenly, the moving column of water can continue travelling through the pipework, creating a pressure drop followed by a pressure surge. This can be made worse if the non-return valve slams shut or if the pressure vessel is unable to cushion the change.

Common pump-related causes include:

• Sudden pump stop/start
• Incorrect VFD settings
• Poor sequencing in duty/standby pump arrangements
• Non-return valve slam
• Undersized or incorrectly charged pressure vessels
• Pressure vessels that have lost charge
• Controls reacting too quickly to small pressure changes
• Lack of system commissioning or maintenance

Variable frequency drives, or VFDs, can help reduce water hammer when correctly set up. However, if ramp-up and ramp-down times are too short, or if the controls are not properly matched to the system, pressure surges can still occur.

Duty/standby and multi-pump booster sets also need correct sequencing. If pumps cut in and out too sharply, or multiple pumps respond at the wrong time, the system can experience unnecessary pressure fluctuation. A well-designed control strategy helps the booster set respond smoothly to demand rather than creating sudden hydraulic shocks.

Pressure vessels are also critical. The right pressure vessel provides a cushion within the system, helping to absorb pressure changes and reduce pump cycling. If the vessel is too small, incorrectly pre-charged or waterlogged, the booster set may short cycle and create further stress on the system.

How to Prevent Water Hammer

Preventing water hammer requires a system-based approach. The solution is not always to replace a single part. In many cases, the best long-term result comes from reviewing the booster set, controls, pressure vessels, valves and pipework together.

Effective ways to prevent water hammer include:

Soft Start and VFD Drives

Soft starters and VFD drives help pumps start and stop more gradually. This reduces sudden changes in flow and helps protect pipework from pressure shock. In booster sets, correctly configured VFDs can improve pressure stability and reduce the risk of water hammer.
The key is correct commissioning. Ramp times, pressure setpoints and control parameters must be suitable for the system. A VFD that is poorly configured can still allow pressure surges.

Correct Non-Return Valve Selection

Non-return valves play an important role in preventing reverse flow. However, the wrong valve type or a poorly performing valve can contribute to valve slam and water hammer.
Selecting the correct non-return valve for the flow rate, pressure and application helps ensure the valve closes at the right time and reduces shock through the pipework.

Surge Vessels and Pressure Vessels

Surge vessels and pressure vessels are among the most important components for controlling pressure fluctuations. In booster sets, the pressure vessel helps maintain system pressure, reduce pump cycling and absorb small changes in demand.

To work effectively, the vessel must be correctly sized, correctly installed and correctly pre-charged. A failed or incorrectly charged vessel can cause rapid pump cycling, unstable pressure and increased risk of water hammer.

Regular pressure vessel checks should form part of planned preventative maintenance. This includes checking the vessel charge, inspecting for signs of failure and confirming it is still suitable for the system demand.

Pipework Redesign

Sometimes, water hammering in pipes is linked to pipework layout or sizing. Undersized pipework, sharp directional changes and excessive flow velocities can increase the risk of pipe hammering throughout the system.

Where required, pipework modifications can help reduce flow velocity, improve system stability and minimise sudden pressure changes. This can reduce hammering water pipes, water surging and pressure shock across the wider pipe network.

Pump Control Sequencing

For multi-pump booster sets, correct pump sequencing is essential. Pumps should be staged smoothly to meet demand without sudden pressure changes.

Good control sequencing can help avoid unnecessary pump starts, reduce short cycling and improve the overall efficiency of the system. It also helps extend the life of pumps, valves, vessels and controls.

Planned Preventative Maintenance

Planned preventative maintenance is one of the most effective ways to reduce the risk of water hammer. Regular checks can identify failing pressure vessels, worn valves, control issues, air in the system and early signs of pump wear before they become major problems.

A booster set maintenance visit should include checks on:

• Booster set operation
• Pump start/stop performance
• VFD settings
• Pressure vessel condition and charge
• Non-return valve performance
• System pressure stability
• Signs of vibration or pipework movement
• Control panel faults or alarms

Which Sites Are Most at Risk?

Any critical or commercial site with pumped water systems can experience water hammer, but some environments are more vulnerable due to high demand, complex pipework or critical operational requirements.

Sites most at risk include:

• Hospitals and healthcare environments
• Education facilities
• Industrial sites
• Commercial buildings
• Correctional facilities/Prisons
• High-rise buildings
• Hotels and leisure facilities
• Manufacturing sites

Large commercial and industrial sites with extensive pipe networks can be particularly vulnerable to a hammer pipeline effect, where pressure shockwaves travel significant distances through the system before becoming visible as noise, vibration or equipment failures.

Booster sets in high-rise buildings are particularly vulnerable because they are often required to maintain pressure across multiple floors. Any instability in pump control, vessel performance or valve operation can quickly affect the wider system.

Hospitals, correctional facilities and industrial sites may also be at higher risk because downtime can have serious operational consequences. In these environments, preventing water hammer is not just about reducing noise. It is about protecting essential infrastructure.

When to Call a Pump Specialist

If you are experiencing water hammering noise, water surging, hammering in water pipes, pump trips or repeated component failures, it is time to call a pump specialist.

Water hammer is often a symptom of a wider system issue. The cause may be linked to pump controls, pressure vessels, non-return valves, pipework design or system commissioning. A specialist assessment can identify the root cause and recommend a long-term solution rather than a temporary fix.

Dura Pump can inspect your booster sets, clean water pumps, heating and cooling pumps and wastewater pumping stations to help diagnose water hammer and pressure-related issues.

Our team can advise on the correct controls, VFD settings, non-return valves, surge protection and pressure vessels needed to protect your system and reduce the risk of future failures.