Diagnosis and correction of water hammer on check valves: shock analysis, closing speed diagnosis and damper selection

1. Problem description & scope of application

This guide addresses the critical phenomenon of water hammer (pressure surge) in piping systems caused by the abrupt closing of check valves. Water hammer can cause significant damage to pipes, pumps, valves and other components, jeopardizing operational safety and causing unplanned downtime. The main symptom is a loud bang or strong vibration, often associated with high pressure spikes, particularly when pumps are switched off or during rapid changes in flow rate.

Affected facilities and systems:

• Industrial pumping stations (water supply, chemical, petrochemical)
• Cooling systems and heating circuits
• Process systems with liquid media
• Energy supply systems

Types of check valves and their influence:

• Swivel flap check valves (DIN EN 16767): Susceptible to slow closing at low flows or rapid slamming at high return flows.
• Spring-loaded lift check valves (DIN EN 13495): Offer faster closing times, but can also cause shocks if the spring strength is incorrect.
• Ball check valves: Rather with smaller nominal diameters, can flutter if the minimum flow is insufficient.

Severity classification:

• Critical: Immediate danger to personnel, system failure, significant environmental impact. Requires immediate action.
• Serious: High material wear, potential consequential damage, high repair costs. Requires prioritized repairs.
• Minor: Minor noise, slight wear. Requires observation and scheduled repair.

2. Safety precautions

ATTENTION: Working on piping systems under pressure or with dangerous media involves considerable risks. Strict adherence to safety regulations is essential to avoid injury or system damage.

• Lockout and securing (Lockout/Tagout - LOTO): Before any work on the system begins, the corresponding shut-off valves must be closed, the pumps must be switched off and secured (locked/tagged) against being switched on again. Energy sources such as electrical supply and compressed air must be interrupted.
• Pressure Relief: The system must be completely depressurized and drained before dismantling components. Residual energy in springs or accumulators must be taken into account.
• Personal protective equipment (PPE): At least safety glasses, safety shoes and protective gloves must be worn. When in contact with aggressive, hot or cold media, additional specialized PPE (e.g. full face protection, chemical protection suits) is required.
• Media-related hazards: Know the properties of the medium (temperature, toxicity, flammability) and take appropriate precautions according to the safety data sheets.
• Hot work: When carrying out welding or cutting work, the risk of fire must be minimized and appropriate permits must be obtained (fire permit).

3. Required diagnostic tools

Specialized measuring devices and tools are essential for precise diagnosis. The selection depends on the specific symptom and system configuration.

4. Checklist for initial assessment

Before starting detailed diagnostic steps, systematic recording of operational data and observations is crucial for narrowing down possible causes.

5. Systematic diagnostic flowchart

This decision tree guides the technician through diagnosis based on the symptoms observed.

1. Symptom: Clear, one-time bang or strong shock when the pump is switched off (classic water hammer).
   1. Initial check:
      • Check the pump control logic: Does the pump stop abruptly or with a ramp?
      • Visual inspection of the check valve for external damage or incorrect installation position.
   2. Pressure transient measurement:
      • Install pressure gauges with high sampling rate (min. 100 Hz) before and after the check valve.
      • Measure the pressure curve during the pump stop.
      • IF Pressure peak after the valve exceeds 1.5 times the operating pressure (alarm limit DIN 2401) THEN probably a valve closing problem. Go to 2.
      • ELSE IF No significant pressure peak, but loud noise THEN Suspect resonance or cavitation. Go to 3.
2. Symptom: Continuous rattling, rattling or fluttering of the check valve during operation.
   1. Initial check:
      • Check the minimum flow of the pump compared to the design of the check valve.
      • Check whether it is a swing flap valve in vertical pipeline.
   2. Vibration measurement (DIN ISO 10816):
      • Measure vibrations on the valve body and on the adjacent pipeline.
      • IF RMS value of the vibration velocity (v_RMS) on the valve exceeds 4.5 mm/s (alarm limit for system components) THEN Suspicion of flap fluttering or loose components. Go to 4.
      • ELSE IF Vibrations primarily in the pipeline, not at the valve THEN Suspicion of flow-induced resonance. Go to 5.
3. Symptom: Pressure fluctuations in the system without obvious noise from the valve.
   1. Flow measurement:
      • Use an ultrasonic flow meter to verify the volume flow.
      • IF Flow fluctuates greatly or shows backflow THEN Suspicion of partial leakage or incomplete closing of the check valve. Go to 6.
      • ELSE Suspicion of higher-level system problems (e.g. pump cavitation, pressure control problems). Document and extend the diagnosis to the entire system.

6. Error-cause matrix

This matrix provides a quick overview of symptoms, likely causes, diagnostic tests and expected results.

7. Root cause analysis for each error

An in-depth analysis of the root causes is crucial in order to solve the problems sustainably and avoid recurrences.

A. Check valve closes too slowly (delay)

Explanation: The valve remains open for too long after the pump stops or during reverse flow. This enables the returning liquid column to be accelerated, which then hits the closing flap with high kinetic energy and causes the water hammer.

• Why it happens:
  • Wear or fatigue of the recoil spring: A weakened spring cannot press the flap into the seat quickly enough. (DIN EN 13495, DIN EN 16767)
  • Contaminants in the valve seat or on the flap: Deposits (dirt, particles, corrosion) can inhibit the closing mechanism or prevent a complete seal.
  • Incorrect valve type for installation position: A swing flap check valve in a vertical pipeline where gravity acts against the flap closing.
  • Oversizing the valve: A valve that is too large has a slower flap and reacts more slowly to flow changes.
• As confirmed:
  • Pressure transient measurement shows a delayed closing movement and a subsequent pressure spike.
  • Visual inspection of the dismantled valve for spring condition, seating surfaces and flap mobility.
  • Acoustic analysis of the closing sound: A dull, delayed thud versus a sharp, quick bang.
• Damage if not repaired:
  • High pressure peaks put pressure on pipeline flanges, weld seams and brackets to the point of material fatigue or breakage.
  • Damage to pump bearings, shaft seals and impellers due to recoil forces.
  • Destruction of measuring devices and other fittings in the system.
  • Increased energy consumption and system inefficiency due to leaks and vibrations.

B. Check valve closes too quickly (missing/insufficient damping)

Explanation: The valve closes extremely abruptly as soon as the backflow begins. The sudden deceleration of the liquid column creates an immediate, extremely high pressure wave.

• Why it happens:
  • Lack of a damping system: Especially with larger valves or systems with high flow speeds, damping is absolutely necessary in order to close the flap smoothly.
  • Incorrect damper adjustment: Hydraulic or pneumatic dampers are incorrectly adjusted, do not offer enough resistance or are defective.
  • Valve Too Small: Although rarely the primary cause of rapid closing, a severely undersized valve that responds too quickly to pressure changes can, in combination with other factors, result in hard hits.
• As confirmed:
  • Pressure transient measurement shows an extremely steep and high pressure peak immediately after the flow crosses zero.
  • Observation of the closing process (with damped valves) shows an abrupt onset of damping or its absence.
• Damage if not repaired:
  • Peak pressures can go far beyond the rated pressure of the pipeline (TÜV critical value), which leads to immediate pipe breakage or flange leaks.
  • Cavitation caused by subsequent negative pressure (vacuum envelope) can destroy material.
  • Severe mechanical damage to the valve itself (seat, flap, hinge), resulting in leakage or total failure.

C. Incorrect valve selection or design

Explanation: The installed check valve is not suitable for the specific operating conditions (pressure, temperature, medium, flow characteristics) or is incorrectly dimensioned.

• Why it happens:
  • Inappropriate valve type: A swing flap valve in a highly pulsating system or with rapid flow changes. A lift check valve that does not fully open at low flow.
  • Incorrect dimensioning: A valve that is too large is often not opened sufficiently and tends to flutter. A valve that is too small causes high pressure losses and can promote cavitation. (VDI 2166 Sheet 2)
  • Lack of consideration of system transients: No analysis of the hydraulic behavior of the entire system when selecting the valve.
• How it is confirmed:
  • Review of the design documents and specifications of the valve compared to the actual operating conditions.
  • Hydraulic calculations to check pressure losses and closing characteristics.
  • Analysis of the flow behavior (ultrasonic flow meter) shows whether the valve is operating in the optimal range.
• Damage if not repaired:
  • Increased wear on the valve due to chattering and incomplete opening/closing.
  • Higher energy consumption of the pump due to unnecessary pressure losses at the valve.
  • Unstable system operation, which may also affect other components.

D. Pump or system transients

Explanation: Water hammer is not primarily triggered by the valve itself, but by rapid pressure changes in the entire system, e.g. by abruptly switching off pumps without delay or rapid load changes.

• Why it happens:
  • Sudden shutdown of large pumps: Without soft start/soft stop control, the liquid column is abruptly stopped, creating a pressure wave.
  • Rapid opening/closing processes of other valves: Rapidly operated valves in the system can also generate pressure peaks.
  • Incorrect design of pressure shock absorbers or missing wind chambers: There are insufficient measures to absorb sudden pressure changes.
• How it is confirmed:
  • Analysis of the control logic of pumps and other system components.
  • Synchronized pressure measurements at different points in the system show the propagation of the pressure wave.
  • Review of the hydraulic design of the entire system.
• Non-remediation damage:
  • System-wide damage that is not limited to a single component.
  • Increased wear on all pressure-carrying components.
  • Potential business interruptions due to failures at critical points.

8. Step-by-step fix procedure

The following measures should be taken after diagnosing the specific cause. Always observe the safety precautions in Section 2.

A. Remedy for valve closing too slowly (delay)

1. Valve cleaning and inspection:
   • Preparation: Depressurize system, apply LOTO.
   • Dismantling: Remove the valve and disassemble it carefully.
   • Cleaning: Thoroughly clean all parts, especially the valve seat, flap and hinges, to remove any dirt and deposits.
   • Inspection of the spring: Check the spring for corrosion, breaks or loss of length. A spring that is more than 5% shorter than its original length or shows visible corrosion damage must be replaced (DIN EN 13495).
   • Check seat and flap: Check for wear, cracks or pitting. Damaged sealing surfaces may require the valve to be reworked or replaced.
   • Assembly: Use new seals, observe valve specifications and torques for flange connections.
2. Adjust valve type (if necessary):
   • Action: If a swing flap check valve is installed in a vertical upflow, replace it with a spring-loaded lift or ball check valve.
   • Specification: Choose a valve with a suitable spring force that ensures quick but cushioned closing. Observe manufacturer's instructions for minimum response pressures.
3. Optimize valve size:
   • Measure: Check the design of the valve. A valve that is too large can cause inertia problems.
   • Specification: Select a valve whose nominal size corresponds to the average flow and allows a minimum opening pressure that prevents chatter.
4. Verification after repair:
   • Carry out a functional test of the valve and observe the closing process.
   • Repeat the pressure transient measurement when the pump stops to confirm the effectiveness of the measures.

B. Remedy if the valve closes too quickly (insufficient damping)

1. Install or adjust hydraulic/pneumatic damper:
   • Action: For undamped valves in critical applications, the installation of an external hydraulic damper (e.g. oil brake) is required.
   • Setting: Adjust the damping rate for existing dampers. The closing time should be set so that it exceeds the critical time T_krit (2L/a, where L is the pipeline length and a is the speed of sound in the medium), but is not unnecessarily extended. Typical values ​​for soft closing: 0.5 to 2.0 seconds.
   • Verification: Pressure transient measurement must show that the pressure peaks are below the permissible limits (e.g. max. 1.2x operating pressure).
2. Replacement with a damped check valve:
   • Measure: Replace undamped valves with types with integrated oil or air dampening, especially for larger nominal diameters.
   • Specification: Select valves that offer adjustable damping characteristics to precisely match system conditions.

C. Remedy for incorrect valve selection or design

1. Valve recalculation and replacement:
   • Action: Perform a detailed hydraulic recalculation of the system. Take into account the minimum and maximum flow, pressure losses and the permissible pressure increase. (VDI 2166 Sheet 2)
   • Specification: Choose a valve that optimally matches the operating point of the system. Double-sprung disc check valves (silent check valves) or axial check valves are often suitable for dynamic systems.
   • Installation: Pay attention to the correct installation position (e.g. horizontal flap valves only in horizontal lines).
2. Verification after replacement:
   • Perform comprehensive commissioning tests, including pressure transient and vibration measurements.
   • Observe system behavior over time under various load conditions.

D. Troubleshoot pump or system transients

1. Optimization of the pump control:
   • Measure: Implement soft start and soft stop ramps for the pumps, especially in systems with large flow rates.
   • Setting: Typical ramp times are between 10 and 30 seconds, depending on the pipeline length and the inertia of the liquid column. The aim is to slow down the pressure drop in front of the check valve.
   • Verification: Monitor the pressure history during start and stop processes to ensure that there are no critical pressure spikes.
2. Installation of pressure shock absorbers (pulsation dampers):
   • Action: Install diaphragm, bladder or bellows pressure shock absorbers near the pump or at critical points in the piping system.
   • Specification: The volume of the damper and the pre-pressure must be precisely adjusted to the maximum system pressure and the expected volume flow fluctuations. (DIN EN 13867)
   • Maintenance: Regular checking of the pre-pressure in the damper is critical for its function.

9. Preventive measures

Implementing proactive strategies to prevent water hammer is more cost-effective than repairing damage.

10. Spare Parts & Components

Having the right replacement parts available is critical to quickly and effectively resolving water hammer problems. All components listed here can be obtained from the UNITEC-D e-catalog.

Other spare parts: flange gaskets (DIN EN 1514-1), screws and nuts (DIN EN ISO 4014/4032), pipe clamps and brackets.

For detailed product information and orders, please visit our UNITEC-D e-catalogue: https://www.unitecd.com/e-catalog/

11. References

• DIN EN 13495: Industrial valves – check valves made of steel.
• DIN EN 16767: Industrial fittings – check valves made of cast iron.
• VDI 2166 Sheet 2: Fluid mechanics in piping systems; Pressure surge in pipelines – causes, calculation and protective measures.
• VDI 3832: Measurement and assessment of vibrations on machines and units using contact and non-contact measurement methods.
• DIN 2401: pipelines; nominal values; pressure, temperature.
• DIN EN 13867: Pressure vessel – hydraulic accumulator; Part 1: General requirements for diaphragm, bladder and piston accumulators.
• TÜV guidelines: Especially for the safe operation of pressure vessels and piping systems.
• Manufacturer manuals for pumps, check valves and damping systems.