Diagnosis & Solution Water Hammer in Check Valves: Analysis, Velocity and Damping

1. Problem Description & Scope

Water hammer, specifically caused by the improper functioning of check valves, manifests as a critical system problem in liquid piping systems. This phenomenon, characterized by abrupt pressure increases and audible 'knocking sounds', can lead to significant damage and operational disruptions. This guide is aimed at diagnosing and resolving water hammer caused by closing check valves too quickly or too slowly in systems such as pumping systems, pressure pipes, cooling circuits, and industrial fluid transport networks.

The severity of water hammer can be classified as:

• Critical: Pipeline rupture, serious damage to pumps, valves or measuring instruments, unplanned production stop, safety risks. Immediate action required.
• Major: Persistent leaks at flanges or fittings, accelerated component wear, reduced equipment life, high maintenance costs. Urgent diagnosis and correction necessary.
• Minor: Occasional knocking noises, mild to moderate vibrations, noise pollution. Potential for escalation to Major or Critical if left untreated.

2. Safety measures

WARNING: Before performing any diagnostic or repair work on any fluid system, strictly adhere to the relevant safety procedures. Ignoring these measures could result in serious injury, property damage or death.

• Lockout/Tagout (LOTO): Ensure that all energy sources (electrical, hydraulic, pneumatic) to the relevant system are fully isolated and locked/tagged according to the NEN 3140 standard for electrical installations and similar procedures for mechanical energy.
• Personal Protective Equipment (PPE): Always wear appropriate PPE, including:
  • Safety glasses (EN 166) or face shield.
  • Hearing protection (EN 352) in the presence of loud noises or pressure relief.
  • Safety gloves (EN 388) suitable for contact with process media (chemically resistant if necessary).
  • Safety shoes (EN ISO 20345) with protective toe cap and sole.
• Stored Energy: Be extremely careful with stored energy in the system. Residual pressure in pipes, hydraulic accumulators or compressed gases must be relieved gradually and in a controlled manner via the appropriate drain points.
• High Temperatures and Pressure: Process media may be under high temperature and/or pressure. Allow systems to cool and bleed completely before disconnecting components. Check the current process conditions carefully.
• Hazardous Media: Identify any hazardous liquids or gases (flammable, corrosive, toxic) and observe specific safety regulations and ventilation requirements, in accordance with REACH and ADR/RID guidelines if applicable.
• Explosive Atmospheres: In potentially explosive atmospheres, all tools and equipment must be ATEX certified (Directive 2014/34/EU).

3. Required Diagnostic Tools

Successful diagnosis of water hammer requires the use of specialized measuring equipment to record the dynamic behavior of the system. The following table provides an overview of critical tools:

4. Initial Assessment Checklist

Before deeper diagnostic testing is performed, a thorough initial assessment is critical. This checklist helps collect basic information that can significantly speed up the diagnosis:

5. Systematic Diagnosis Flow Chart

This decision tree guides you through a systematic diagnostic process to identify the root cause of water hammer in check valves. Start with the most likely scenarios.

1. Symptom: Water hammer audible shortly after pump SWITCH OFF.
   1. Diagnosis: Check valve closing too slowly.
      1. Check the type of check valve:
         • If swing check valve: Is the valve disc too heavy or the distance to be covered is too large, resulting in slow closure due to inertia of the disk and the returning fluid column?
         • If lift valve: Is the spring weakened or dirty, causing the valve not to close quickly enough?
         • If axial check valve: Is the spring broken or the damper defective/dirty?
      2. Measure fluid velocity and direction (with ultrasonic flow meter): Is significant reverse flow detectable before valve closure? This confirms a late closure.
      3. Record pressure transients (with high-speed pressure sensor): Is there a significant drop in pressure followed by a sharp pressure spike when the valve finally closes and impinges on the returning fluid column? (> 1.5x nominal pressure, duration < 50ms).
   2. Conclusion: If the valve closes too slowly, the fluid column will change direction and build up velocity in the reverse direction before the valve closes, causing a hard impact upon closure.
2. Symptom: Water hammer audible shortly after pump ON or sudden CONTROL VALVE closing downstream.
   1. Diagnosis: Too fast closing of check valve OR insufficient damping.
      1. Check the type of check valve:
         • If standard hinge valve or lift valve without damping: Is the valve closed too quickly, possibly due to too rapid acceleration of the liquid column or a disc that is too heavy that closes immediately when the flow rate decreases rapidly?
         • If check valve with damper (oil/air): Does the damper function correctly? Is the damper fluid level or viscosity OK? Is the damper setting correct for the current process conditions?
      2. Record pressure transients: Is there a very rapid increase in pressure immediately after closure, without prior significant backflow?
      3. Check pipe diameter and fluid velocity: Is the average fluid velocity in the pipe too high (above 3 m/s for water), increasing the impact?
   2. Conclusion: Too fast closure or insufficient damping leads to an abrupt stop of the liquid column, generating a high and short pressure peak.
3. Symptom: Continuous water hammer or 'chattering' of check valve in partially open position.
   1. Diagnosis: Valve chattering due to insufficient flow or incorrect sizing.
      1. Measure the current flow through the valve: Is the flow significantly lower than the design flow of the valve, so that the valve disc does not remain fully open and moves continuously under fluctuating flow?
      2. Check check valve sizing: Is the valve selected too large for the minimum or average flow in the system, causing the valve to remain stable in the open position?
      3. Inspect the spring (if applicable): Is the spring too weak, not providing enough pressure to the valve disk to remain stable?
   2. Conclusion: Chattering leads to accelerated wear of the valve components, leakage, and eventually to valve failure.

6. Error Cause Matrix

This matrix combines common symptoms with likely causes, diagnostic tests, and expected results that confirm the cause. The likely causes are listed from most to least likely.

7. Root Cause Analysis for Each Error

A deep understanding of the root causes is essential for sustainable solutions.

7.1. Check valve closing too slowly

Why it happens: Especially with conventional swing check valves with a heavy valve disc in horizontal installations. When the pump stops, the fluid velocity gradually drops to zero and then reverses (backflow) due to gravity or pressure from downstream. The valve disk takes some time to move and close completely. During this period the returning liquid column builds up speed. When the valve disc finally closes, this fast-moving mass is abruptly stopped, generating a significant pressure spike – water hammer.

How to confirm: The pressure transient analysis will show a characteristic pattern: a gradual drop in pressure followed by a period of slight underpressure (due to 'stretching' of the liquid column during backflow), and then a very abrupt, high pressure peak upon closing the valve. The ultrasonic flow meter will record backflow before impact.

Damage if unresolved: Continuous recurrence of this impact can lead to:

• Fatigue failure of the valve housing, hinges or mounting points.
• Damage to the valve sealing surfaces, resulting in leakage and reduced efficiency.
• Damage to upstream pumps (bearing damage, shaft breakage) due to reverse impact forces.
• Structural damage to pipes and pipe supports, with risk of catastrophic rupture.
• Cavitation erosion if vapor bubbles implode under the rapid pressure fluctuations.

7.2. Closing the check valve too quickly (insufficient damping)

Why it happens: This scenario occurs when a check valve closes too quickly, without enough damping to gradually absorb the kinetic energy of the fluid column. This is often the case with light valve discs in spring-loaded check valves or axial check valves that are not equipped with an external damper, or where the damper is defective or incorrectly adjusted. It can also occur if the fluid velocity in the line is too high, giving the valve insufficient time to respond to rapid flow changes.

How to confirm: The pressure transient analysis shows a very short, but extremely high pressure spike immediately after valve closure. Little or no backflow will be observed before closing, which distinguishes it from closing too slowly. Vibration measurements will reveal high frequency peaks (>15 mm/s RMS) on the valve body and direct pipe sections.

Damage if unresolved: The consequences are similar to closing too slowly, but the damage can occur faster and more severely:

• Immediate damage to weak points in the pipe (e.g. welds, flanges, bends).
• Danger of breakage for brittle components such as manometers or flow meters.
• Accelerated fatigue of valve components due to high frequency vibrations.
• Removal of pipe supports and suspensions.

7.3. Valve chattering due to insufficient flow or incorrect sizing

Why it happens: Chattering occurs when a check valve does not remain stable in the fully open or fully closed position. This is often a result of sizing the valve for too high a nominal flow, while the actual flow in the system, especially at part load, is considerably lower. The pressure drop across the valve at low flow is insufficient to keep the valve disc stably open against gravity or spring force. The disc then oscillates between open and closed, causing constant impact and vibration.

How to confirm: Ultrasonic flow measurement will show low, fluctuating flow through the valve. A sound meter will register a repetitive 'ticking' or 'rattling'. Visual inspection (if possible) or disassembly of the valve will show obvious wear patterns (e.g. 'pitting' or 'erosion') on the seat and valve disc caused by the constant back and forth movement.

Damage if unresolved:

• Accelerated wear of valve seat and valve disc, leading to permanent leakage and loss of functionality.
• Loosening of internal valve components, with risk of blockages downstream.
• Possible fatigue fracture of the valve shaft or hinges.
• Noise pollution and vibrations spreading through the pipe system.

8. Step-by-Step Resolution Procedures

The solution to water hammer often requires adjustment of the check valve type, damping or operating parameters. Follow these procedures carefully after LOTO.

8.1. For water hammer due to too slow valve closing:

1. Replace with a suitable valve type:
• Consider a spring loaded axial check valve designed for fast response even at low flow rates. These valves have a short stroke and a spring that forces the closure. Ensure correct spring selection for the operating condition.
• Alternative: a check valve with oil damper (damped check valve) that allows a controlled closing speed, adjustable between 0.5 and 5 seconds.
• Choose a valve with low inertia of the moving parts, in accordance with EN 16767.
2. Optimize the spring rate (if applicable):
• For spring-loaded valves, ensure that the spring has sufficient stiffness to close the valve disk quickly and stably once the fluid velocity decreases to zero. A spring that is too weak will delay the closing.
3. Decrease fluid velocity:
• If possible, reduce the average fluid velocity in the discharge line by installing a larger diameter line or adjusting the pump capacity. A guideline for water is a maximum speed of 2-3 m/s for pressure pipes to minimize water hammer.
4. Installation of water hammer arrestors:
• Consider installing a hydropneumatic surge vessel upstream of the check valve. These absorb the energy of the returning column.
5. Post-repair verification: After replacement/adjustment, repeat pressure transient analysis and ultrasonic flow measurement. There must be no significant backflow and the pressure peak at closure must be within acceptable limits (max. 1.25x nominal pressure).

8.2. For water hammer due to valve closing too quickly (insufficient damping):

1. Install or adjust damper:
• Use a check valve with an adjustable hydraulic damper. Adjust the damper so that the closing speed of the valve disk is slowed, causing the fluid column to come to a stop more gradually. Typical closing speeds for damped valves range from 1 to 10 seconds, depending on pipe length and fluid velocity.
• Check the damping medium (oil) for contamination or loss. Replace if necessary.
2. Select a more suitable valve:
• Choose a valve specifically designed to prevent rapid closing and water hammer, such as an axial flow check valve with hydraulic damping (API 594).
3. Optimize pump switching protocols:
• Consider using soft starters or variable frequency drives (VFDs) for pumps to smooth the acceleration and deceleration of the liquid column. This reduces the dynamic forces on the valve.
4. Post-repair verification: Perform pressure transient analysis and vibration measurement again. The pressure peak must be significantly reduced and the vibration levels on the pipes and valve body must remain below the alarm threshold (e.g. < 7.1 mm/s RMS for critical equipment, in accordance with ISO 10816).

8.3. For flapping check valve:

1. Resizing of the valve:
• The most effective solution is to install a smaller sized check valve that better matches the typical (minimum) flow rate in the system. A smaller valve body and a lighter disc respond better to low flows.
• Consult the valve manufacturer or UNITEC-D E catalog for the recommended minimum flow rate to keep the valve fully open.
2. Use of spring loaded valves:
• A spring-loaded check valve (such as an axial or lift valve) can help keep the valve disc stable in the open or closed position, even during fluctuating low flow rates. The spring force prevents chattering.
3. Installation of a bypass pipe:
• If the flow rate varies greatly, a bypass with a smaller, properly sized check valve for low flow rates may provide a solution.
4. Post-repair verification: After replacement/adjustment, monitor the noise and vibration of the valve under different operating conditions (low, medium, high flow). The chattering should have disappeared completely.

9. Preventive Measures

Prevention is better than cure. Implement the following preventative measures to minimize recurring water hammer problems:

10. Spare Parts & Components

Having the right spare parts available in a timely manner is crucial for quickly solving water hammer problems and minimizing downtime. UNITEC-D offers an extensive range of high-quality components that comply with the relevant standards (CE, TUV).

For a complete overview of compatible components and the most current specifications, visit our UNITEC-D E-catalog at https://www.unitecd.com/e-catalog/.

11. References

• NEN-EN 13445: Unfired pressure equipment – Rules for design, manufacture, inspection and testing.
• ISO 4126-1: Safety valves – Part 1: General requirements.
• EN 16767: Industrial valves – Check valves.
• ISO 10816: Mechanical vibration – Measurement and assessment of machine vibration.
• AWWA M11: Manual of Water Supply Practices – Steel Pipe – A Guide for Design and Installation.
• API 594: Check Valves: Flanged, Lug, Wafer, and Butt-welding Ends.
• Hydraulic Institute (HI) Standards: Pump Intake Design, Piping and Valve Design.
• OEM manuals for specific pump and valve manufacturers.
• Related UNITEC-D maintenance manuals: 'Diagnosis of pump cavitation', 'Vibration analysis of rotating machines'.