Why Does a Check Valve Make Banging Noises? Water Hammer Analysis and Selection of Swing, Lift, and Dual-Plate Check Valves

In water supply, circulation water, pumping stations, and industrial piping systems, operators often encounter the same problem:

When the pump stops, a sudden “bang” comes from the pipeline. Sometimes it sounds as though someone has struck the pipe with a hammer. In other cases, the check valve disc repeatedly slams inside the valve, creating sharp and rapid noises.

In more serious cases, the following problems may also occur:

1. Flange gaskets or fasteners become loose;
2. Pressure gauge needles fluctuate violently;
3. Pipes and supports vibrate noticeably;
4. Valve discs, seats, and hinge components wear rapidly;
5. Pumps, instruments, and other piping equipment are subjected to impact loads.

When this happens, the first reaction on site is often:

“Is the check valve defective?”

Manufacturing quality can certainly cause disc sticking, abnormal sealing, or loose internal components. However, in many cases, check valve noise is mainly related to three factors:

1. Improper pipeline flow rate or velocity;
2. Incorrect check valve structure selection;
3. Incorrect installation direction or location.

When a check valve makes banging noises, it is often a warning that the valve design, flow conditions, and installation arrangement are not properly matched.

What Is the Function of a Check Valve?

A check valve, also called a non-return valve or one-way valve, is designed to allow flow in one direction and prevent reverse flow.

Its basic operating process is as follows:

1. During forward flow, fluid force or differential pressure pushes the disc open;
2. When the flow decreases or stops, the disc begins to close under gravity or spring force;
3. When reverse flow occurs, back pressure pushes the disc against the seat and prevents backflow.

A check valve usually does not require manual operation or an electric actuator. It operates automatically through fluid movement, pressure difference, disc weight, and spring force.

The problem often occurs during this automatic closing process.

If the valve closes too slowly, reverse flow may already have developed before the disc reaches the seat. The reverse-flowing fluid then forces the disc violently against the seat, producing a loud impact.

If the valve closes too quickly, the moving fluid may be stopped abruptly. The fluid’s kinetic energy is then converted into a pressure wave, which can also create water hammer and pipeline shock.

Therefore, a check valve is not considered properly selected simply because it can close.

The key requirement is:

The check valve must close at the correct time and at a speed that matches the piping system.

Main Causes of Check Valve Banging

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Check valve noise can generally be divided into two categories: water hammer and disc slamming.

Water Hammer

Water hammer usually occurs when a pump stops suddenly, a valve closes rapidly, or the fluid velocity changes sharply.

The fluid inside a pipeline has inertia. When the moving fluid is suddenly slowed or stopped, its kinetic energy is converted into a pressure wave. This wave travels and reflects through the piping system, creating a strong impact noise.

Water hammer usually sounds heavy, as though the pipe has been struck forcefully. It may also be accompanied by:

1. Visible pipeline vibration;
2. Rapid pressure gauge fluctuation;
3. Shock loads on flanges and pipe supports;
4. Repeated vibration in certain pipe sections.

When troubleshooting water hammer, the check valve should not be inspected alone. The entire system must be considered, including pump shutdown characteristics, pipeline length, fluid velocity, elevation difference, pipe supports, and slow-closing measures.

Disc Slamming or Chattering

Disc slamming usually occurs when the check valve cannot remain steadily in the fully open position.

When flow rate or velocity is too low, the fluid force may not be sufficient to fully open the disc. The disc may remain partially open and repeatedly strike the seat or stop as the flow fluctuates.

This noise is usually sharper and more continuous, similar to rapid clicking or tapping.

Common causes include:

1. Actual flow below the minimum stable opening flow;
2. Oversized valve diameter;
3. Unstable flow at the pump outlet;
4. Valve installed too close to elbows, tees, or pump discharge;
5. Incorrect installation direction;
6. Sticking of the disc, guide, hinge, or spring.

Although disc slamming and water hammer may occur together, their troubleshooting priorities are different.

Why Are Swing Check Valves Prone to Slamming?

A swing check valve uses a disc that rotates around a hinge pin inside the valve body, similar to a door.

During forward flow, the fluid pushes the disc open. When the flow stops or reverses, the disc returns to the seat under its own weight and reverse pressure.

Swing check valves generally have the following characteristics:

1. Relatively open flow passage;
2. Low flow resistance;
3. Low pressure loss;
4. Suitable for medium and large pipe sizes;
5. Commonly used in water supply, circulation water, and general industrial pipelines.

However, swing check valves also have one important characteristic: the disc has a relatively long travel and closes more slowly.

When a pump suddenly stops, the fluid first decelerates and may then begin to reverse. If the disc has not fully closed before reverse flow develops, the reverse-moving fluid can force the disc violently against the seat.

Swing check valves are therefore more likely to produce water hammer or slamming in the following conditions:

1. Pump discharge lines;
2. Long-distance transmission pipelines;
3. High flow velocity;
4. Large elevation differences;
5. Frequent pump starting and stopping;
6. Rapid reverse flow after pump shutdown;
7. Systems without cushioning or slow-closing measures.

For these applications, slow-closing check valves, tilting-disc check valves, axial-flow check valves, or other fast-response designs may be considered.

A pump discharge check valve should not be selected based only on nominal size and pressure class. The fluid deceleration process and maximum reverse velocity after pump shutdown are often more important.

Why Do Lift Check Valves Produce Continuous Knocking?

A lift check valve has a disc that moves vertically along an internal guide.

During forward flow, fluid force lifts the disc. When the flow decreases, stops, or reverses, the disc falls back onto the seat under gravity or spring force.

Lift check valves generally have the following characteristics:

1. Short disc travel;
2. Direct closing action;
3. Good sealing performance;
4. Suitable for small sizes and higher-pressure service;
5. Sensitive to installation direction and fluid cleanliness.

Incorrect Installation Direction

A conventional lift check valve is usually installed in a horizontal pipeline so that the disc can move vertically and freely.

If the valve is installed in a position that does not match its design, the disc may tilt, rub, or stick, resulting in:

1. Incomplete opening;
2. Incomplete closing;
3. Slow disc movement;
4. Seat leakage;
5. Continuous disc vibration.

Some specially designed lift or spring-loaded check valves can be installed in vertical pipelines, but this must be confirmed according to the manufacturer’s installation instructions.

Insufficient Flow

A lift check valve relies on fluid force to raise the disc.

If the actual flow is too low, the disc may open only slightly and move repeatedly near the seat, causing continuous knocking.

This situation is common when:

1. The valve is oversized;
2. The system operates continuously at low load;
3. Pump flow changes frequently;
4. Pipeline velocity is too low;
5. Disc weight or spring force does not match the actual flow.

A lift check valve is not necessarily superior to a swing check valve. It is simply designed for a different range of applications.

Lift check valves are often suitable for small-size, high-pressure, stable-flow applications requiring good sealing. They should be selected carefully for large sizes, low velocities, or fluids containing particles.

Can a Dual-Plate Check Valve Completely Eliminate Water Hammer?

A dual-plate check valve, also called a dual-disc wafer check valve, usually has two semicircular plates and springs that assist closing.

Compared with a conventional swing check valve, the plates are lighter and have shorter travel, allowing the valve to respond more quickly to flow changes.

Its main advantages include:

1. Compact construction;
2. Short face-to-face dimension;
3. Relatively low weight;
4. Fast closing response;
5. Suitable for wafer installation;
6. Commonly used at pump outlets and in limited-space piping.

Although dual-plate check valves can reduce reverse flow and closing impact in many applications, they are not a universal solution to water hammer.

Spring Force Too High

If the springs are too stiff, the fluid force at low flow may not be sufficient to fully open the plates.

This can lead to:

1. Plates remaining partially open;
2. Increased local velocity;
3. Higher valve pressure drop;
4. Disc vibration;
5. Accelerated fatigue of springs and plates.

Spring Force Too Low

If the spring force is too weak, the plates may not close quickly enough.

By the time the valve closes, reverse flow may already have developed, so water hammer and slamming may still occur.

Contaminated Fluid

A dual-plate check valve contains moving parts such as plates, hinge pins, and springs.

If the fluid contains particles, fibers, deposits, or scale-forming substances, these components may stick, wear, or corrode, reducing long-term reliability.

Therefore, the following factors should be considered when selecting a dual-plate check valve:

1. Normal and minimum flow rate;
2. Pipeline velocity;
3. Allowable pressure loss;
4. Fluid cleanliness;
5. Spring material and spring force;
6. Flow change after pump shutdown.

How to Select Swing, Lift, and Dual-Plate Check Valves

Check Valve Type	More Suitable Applications	Main Advantages	Common Problems
Swing check valve	Medium and large pipelines, low pressure loss, relatively stable flow	Low flow resistance, open flow path, suitable for larger sizes	Long closing travel; prone to disc slamming when reverse flow is significant
Lift check valve	Small sizes, high pressure, stable flow, high sealing requirements	Short closing travel, direct action, good sealing	Disc chattering under low flow; sensitive to installation direction
Dual-plate check valve	Pump outlets, limited installation space, applications requiring faster closing	Compact structure, fast closing, short installation length	Improper spring selection may increase pressure loss or cause vibration; contamination may cause sticking

This table is only suitable for preliminary selection.

A proper check valve selection should also consider:

1. Nominal pipe size;
2. Normal and minimum flow rate;
3. Design flow velocity;
4. Operating and design pressure;
5. Fluid type and temperature;
6. Fluid cleanliness;
7. Pipeline installation direction;
8. Pump starting and stopping method;
9. Pipeline length and elevation difference;
10. Allowable pressure loss;
11. Water hammer and low-noise requirements.

A common selection mistake is to focus only on the term “check valve” without considering how the disc moves.

7. Which Piping Systems Are Most Likely to Experience Water Hammer?

Pump Discharge Lines

Pump discharge lines are among the most common locations for check valve water hammer.

When a pump suddenly stops, the forward-moving fluid decelerates and may reverse under static pressure or elevation difference.

If the check valve closes too late, the disc is slammed shut by reverse flow. If it closes too quickly, the fluid may be stopped abruptly, creating a strong pressure wave.

Pipelines with Large Elevation Differences

When fluid is pumped from a lower elevation to a higher elevation, the fluid in the upper section tends to fall back after pump shutdown.

The greater the elevation difference and pipeline length, the more significant the reverse flow and pressure fluctuation may become.

Systems with Frequent Flow Fluctuation

When the system flow changes continuously, the check valve disc may not remain steadily in the fully open position.

Repeated disc movement may result in:

1. Repeated impact between the disc and seat;
2. Wear of hinge pins and hinge components;
3. Spring fatigue;
4. Damage to sealing surfaces;
5. Shortened valve service life.

Check Valves Installed Near Elbows, Tees, or Pump Outlets

Immediately downstream of a pump, elbow, or tee, the flow profile is often unstable and may include swirl, pulsation, asymmetric flow, and non-uniform velocity distribution.

If a check valve is installed in such a location, the disc may experience uneven fluid forces, causing vibration or uneven wear.

Where space permits, a suitable straight pipe length should be provided according to the piping arrangement, pump type, and valve manufacturer’s recommendations.

What Should Be Checked First When a Check Valve Becomes Noisy?

When a check valve begins making noise, replacing it immediately with the same valve type is not always the best solution.

If the flow velocity, installation location, or pump shutdown behavior remains unchanged, the new valve may develop the same problem.

The following troubleshooting sequence is recommended.

Step 1: Identify When the Noise Occurs

Determine whether the noise occurs:

1. At pump startup;
2. During normal operation;
3. During flow adjustment;
4. At pump shutdown;
5. Several seconds after pump shutdown.

If the noise mainly occurs during startup or low-flow operation, the disc may not be opening fully.

If the noise occurs at shutdown, reverse flow, closing speed, and water hammer should be investigated.

Step 2: Identify the Type of Noise

A continuous, sharp tapping noise usually indicates disc chattering or slamming.

A sudden, heavy bang accompanied by pipeline vibration and pressure fluctuation is more likely to be water hammer.

Step 3: Check Actual Flow and Valve Size

If the check valve is oversized, the actual flow may not be sufficient to hold the disc fully open.

Check the following:

1. Actual operating flow;
2. Minimum operating flow;
3. Fluid velocity in the pipe;
4. Minimum stable opening flow of the check valve;
5. Actual disc opening position.

Many check valves are not damaged. They are simply operating continuously outside their stable flow range.

Step 4: Check Installation Direction and Location

Inspect the following items:

1. Whether the body arrow matches the flow direction;
2. Whether the lift check valve is installed as required;
3. Whether the hinge pin direction of the dual-plate check valve is correct;
4. Whether the valve is installed too close to an elbow, tee, or pump outlet;
5. Whether the pipeline has significant misalignment or installation stress;
6. Whether the disc can move freely.

Step 5: Inspect Internal Components

After shutdown and pressure release, inspect:

1. Whether the disc is sticking;
2. Whether the hinge pin is loose or worn;
3. Whether the spring is broken or fatigued;
4. Whether the sealing surface is damaged;
5. Whether foreign material is trapped inside;
6. Whether the disc shows uneven wear;
7. Whether the guide parts are deformed.

Step 6: Analyze the Entire Piping System

For long-distance water transmission, frequent pump operation, or large elevation differences, the system may require a combination of measures such as:

1. Slow-closing check valves;
2. Water hammer arrestors;
3. Air valves;
4. Accumulators or pressure-stabilizing devices;
5. Variable-frequency control;
6. Optimized pump startup and shutdown times;
7. Adjusted valve closing characteristics;
8. Reinforced pipe supports.

Water hammer is a system-level problem and usually cannot be solved by a conventional check valve alone.

What Information Should Be Provided When Purchasing a Check Valve?

Some purchase specifications only state:

DN100, PN16, check valve, flanged connection.

This description is not sufficient for accurate valve selection.

Swing, lift, dual-plate, axial-flow, and slow-closing designs are all check valves, but their movement, closing speed, and suitable applications are very different.

The following information should be provided during procurement or inquiry.

Valve Structure

Specify whether the required valve is:

1. Swing check valve;
2. Lift check valve;
3. Dual-plate check valve;
4. Axial-flow check valve;
5. Slow-closing check valve;
6. Other specified design.

Installation Location

State whether the valve will be installed at:

1. Pump discharge;
2. Horizontal pipeline;
3. Vertical pipeline;
4. Long-distance water transmission line;
5. Equipment outlet;
6. High-elevation piping system.

Fluid and Operating Conditions

Provide:

1. Fluid name;
2. Fluid temperature;
3. Operating pressure;
4. Normal flow rate;
5. Minimum flow rate;
6. Whether the fluid contains particles or impurities;
7. Whether the system starts and stops frequently;
8. Whether the flow fluctuates.

Connection and Testing Standards

Flanged connections may refer to the following standards depending on project requirements:

1. GB/T 9113;
2. HG/T 20592;
3. ASME B16.5.

Valve inspection and pressure testing may refer to:

1. GB/T 13927;
2. API 598.

The final standard should be determined by the project specification, end-user requirements, and piping design documents.

Special Functional Requirements

For check valves installed at pump outlets, the inquiry should preferably indicate:

1. Whether water hammer protection is required;
2. Whether slow-closing performance is required;
3. Whether closing impact must be limited;
4. Whether low-noise operation is required;
5. Allowable system pressure loss;
6. Normal and emergency pump shutdown time.

This information allows the manufacturer to determine whether a conventional check valve is suitable and helps prevent selection based only on the lowest price.

Should a Check Valve Close as Fast as Possible?

If a check valve closes too slowly, significant reverse velocity may develop in the pipeline. When the disc finally closes, severe slamming may occur.

However, if the valve closes too quickly, it may abruptly stop high-velocity fluid and create a large pressure surge.

Therefore, faster closing does not automatically mean better water hammer protection.

A properly controlled closing process should:

1. Begin before significant reverse flow develops;
2. Prevent the disc from striking the seat at excessive velocity;
3. Avoid abrupt changes in fluid velocity;
4. Match the pump shutdown characteristics and the dynamic behavior of the piping system.

The correct check valve should be selected by considering pump characteristics, pipeline length, fluid velocity, elevation difference, installation location, allowable pressure loss, and fluid cleanliness.

Frequently Asked Questions

Why does a check valve keep making a tapping noise?

A continuous tapping noise is usually related to disc vibration. Common causes include low flow, oversized valve diameter, incomplete disc opening, unstable pump discharge flow, or unsuitable spring force.

Is it normal for a check valve to make one loud bang when the pump stops?

A slight opening or closing sound may be normal. However, if the sound is heavy and accompanied by pipeline vibration, severe pressure gauge fluctuation, or loose flanges, reverse flow and water hammer should be investigated.

Can a dual-plate check valve completely eliminate water hammer?

Not necessarily. A dual-plate check valve has shorter disc travel and can reduce closing impact in many pump discharge applications. However, its performance still depends on flow rate, spring force, pipeline length, elevation difference, and pump shutdown behavior.

Conclusion

A banging check valve does not necessarily mean that the valve is defective.

In many cases, the real causes are insufficient flow, incorrect valve structure, improper installation, reverse flow after pump shutdown, or pressure surges in the piping system.

Swing check valves offer low flow resistance but require careful consideration of closing travel and reverse velocity. Lift check valves have short closing travel but are more sensitive to flow and installation direction. Dual-plate check valves respond quickly but still require correct spring selection, acceptable pressure loss, and clean fluid conditions.

A check valve should not be selected based only on nominal size and pressure class, and it should not simply close as fast as possible.

Only by considering the valve structure, pump operating characteristics, pipeline velocity, installation location, and water hammer risk together can disc slamming, pipeline vibration, and equipment damage be effectively reduced.