Diagnosing and Remedying Check Valve Water Hammer: Analysis of Slamming, Closing Speed, and Damper Selection

1. Description of the Problem and Scope of Application

Water hammer caused by rapid closing of a check valve is a critical phenomenon in industrial piping systems. It occurs when fluid flow changes direction or stops abruptly, causing the valve to close rapidly and generating pressure waves that propagate through the system. This can lead to significant mechanical damage to pipelines, fittings, pumps and other equipment.

Typical symptoms:

• A loud "clap" or "knock" in the pipeline when changing the operating mode of the pump (start, stop) or other flow source.
• Intense vibration of the pipeline and fittings.
• Sudden, short-term pressure jumps recorded by manometers or sensors.
• Leaks in flange connections or seals.
• Destruction or deformation of pipeline elements and supports.
• Damage to the internal components of check valves (disc, seat, spring).

Affected Equipment:

Systems with pumping stations, long pipelines, cooling systems, water supply, as well as in the chemical and oil and gas industries, where liquids are transported, are most prone to water hammer. This applies to both pure liquids and suspensions.

Classification of Severity:

• Critical: Immediate risk of destruction of the pipeline, equipment, stoppage of production, threat to the safety of personnel. Requires immediate intervention.
• Significant: Constant, intense noise and vibration, leading to accelerated wear, leaks, but not a direct threat of disaster. Needs planned elimination.
• Minor: A light, intermittent noise that does not cause visible damage but is an indicator of a potential problem. Needs monitoring and prevention.

Compliance with Standards:

Diagnosis and elimination of water hammers must comply with national and international standards, such as DSTU EN 12266-1 (Industrial pipeline fittings. Testing of valves), ISO 4126 (Safety valves) and relevant occupational safety regulations.

2. Precautions

SAFETY PRECAUTIONS: All safety procedures must be carefully followed before any intervention in piping systems under pressure or systems containing hazardous fluids. Failure to follow these instructions could result in serious injury, death, or substantial property damage.

• LOCKOUT / TAGOUT (LOTO): Always perform the LOTO procedure for all power sources (electrical, hydraulic, pneumatic) of equipment being serviced. Make sure that the pumps cannot be started accidentally.
• RESIDUAL ENERGY: Pressurized systems can store significant amounts of energy. Make sure all pressure is relieved and fluid is drained before disassembly. Use appropriate pressure relief points.
• PPE (Personal Protective Equipment): Be sure to use appropriate PPE: safety glasses or a face shield, protective gloves (chemically resistant if necessary), safety shoes, hearing protection.
• HAZARDOUS SUBSTANCES: If the system contains aggressive, toxic, hot or other hazardous liquids, follow special handling protocols, including the use of specialized PPE and ventilation.
• HOT SURFACES: Handle equipment that may be hot with care. Use heat-resistant gloves.

3. Necessary Diagnostic Tools

The following list of tools is required for accurate diagnosis of hydraulic shock of the non-return valve:

4. Initial Assessment Checklist

Before starting a detailed diagnosis, it is necessary to collect and analyze initial data. This will help narrow down potential causes and determine next steps.

5. Systematic Flow of Diagnostics

This diagnostic flow will help you consistently identify the root cause of a check valve water hammer.

1. Initial Observation: A loud "pop" or "thump" in the piping when the pump stops.
   1. Check 1: Visually inspect the check valve.
      1. Result: The valve is installed correctly, the flow arrow corresponds to the direction of fluid movement.
         • Go to 1.b.
      2. Result: The valve is installed incorrectly (for example, the arrow is against the flow).
         • Probable Cause: Incorrect valve installation.
         • Actions: Reinstall the valve according to the manufacturer's instructions.
   2. Check 2: Estimation of pump stall speed.
      1. Result: The pump stops instantly (without smooth coasting).
         • Probable Cause: Sudden stoppage of the pump creating rapid backflow.
         • Actions: Consider the introduction of soft start/stop devices (Soft Starter, VFD).
      2. Result: The pump has a controlled stop.
         • Go to 1.c.
   3. Check 3: Check valve closing time measurement.
      1. Use an ultrasonic tester or a high-speed pressure recorder (if it is possible to track the movement of the disk or the nature of the pressure change).
         • Result: Valve closing time > 0.5 seconds (for DN valves < 100 мм) або > 1 second (for DN > 200 mm valves).
           • Probable Cause: Excessive inertia of the liquid column causing water hammer when slowly closing the valve against reverse flow.
           • Actions: Consider installing an accelerated closing valve (spring-loaded, non-shock) or damper.
         • Result: Valve Close Time < 0.2 секунди.
           • Probable Cause: Valve closes too quickly before backflow has time to fully establish, causing water hammer from flow capture.
           • Actions: Consider installing a controlled closing valve (with hydraulic damper) or increasing the pump run time.
2. Initial Observation: Constant vibration and noise in the pipeline, especially during stable operation.
   1. Check 1: Vibration measurement on the valve body and adjacent pipeline.
      1. Result: Vibration speed > 7.1 mm/s (according to ISO 10816, for unlimited operation).
         • Probable Cause: Mechanical wear of internal valve components (disc, seat, axle) or resonance with natural frequencies of the pipeline.
         • Actions: Dismantling and visual inspection of the valve; analysis of the frequency spectrum of vibration.
      2. Result: Vibration speed < 4.5 мм/с.
         • Go to 2.b.
   2. Check 2: Measure pressure and flow in the system.
      1. Result: Pressure or flow fluctuates significantly.
         • Probable Cause: Unstable operation of the pump, control valves or fluctuating consumption causing frequent opening/closing of the check valve.
         • Actions: Diagnose the causes of system instability.
      2. Result: Pressure and flow are stable.
         • Go to 2.c.
   3. Check 3: Analysis of compliance of the valve with operating conditions.
      1. Result: Installed valve (e.g. cotton) is not designed for systems with frequent flow changes or high velocities.
      2. Probable Cause: Wrong type of check valve for this application.
      3. Actions: Replacing the valve with a more suitable one (for example, spring-loaded or controlled closing).
3. Initial Observation: Leaks in flanged joints or pipe failure.
   1. Check 1: Measurement of peak pressures using a high-speed recorder.
      1. Result: Peak pressures exceed 1.5-2.0 times the working pressure of the system (for example, working 10 bar, peak > 15-20 bar).
         • Probable Cause: Uncontrolled water hammer generating excessive loads on the system.
         • Actions: Detailed analysis of the system and selection of measures to reduce water hammer (see section 8).
      2. Result: Peak pressures do not exceed 1.3 times the working pressure.
         • Probable Cause: Other causes of leaks are possible (poor installation, worn seals), or water hammer is a minor factor.
         • Actions: Check the quality of the installation of the flanges, the condition of the gaskets, and the conformity of the tightening torque of the bolts.

6. Malfunction-Cause matrix

This matrix will help you quickly identify the most likely causes of water hammer based on the observed symptoms.

7. Analysis of the Root Causes of Each Malfunction

7.1. Excessive Backflow Velocity and Liquid Inertia

Explanation: This is the most common cause of water hammer. When the pump suddenly stops, the column of liquid in the pipeline continues to move forward by inertia. The pressure at the outlet of the pump drops, and the pressure in the upstream system causes the fluid to reverse direction and accelerate back to the pump. If the check valve has a large disc travel or a slow closing mechanism (such as a standard rotary or poppet valve), it will not have time to fully close before the backflow has gained significant velocity. When the valve finally closes, it abruptly shuts off the flow of fluid already moving in the reverse direction, creating a peak pressure wave.

Confirmation: Confirmed by high-speed pressure recording. A characteristic feature is a sharp pressure peak that exceeds the working pressure by 2-3 times, which occurs immediately after the valve closes. You can also observe a rapid drop in pressure after the pump is turned off, followed by a sharp jump. Analysis of this data allows calculation of backflow velocity and momentum.

Consequences: Repeated hydraulic shocks cause fatigue of the pipeline material, destruction of flange connections, damage to the internal components of the valves (deformation of the disc, axis, wear of the seat), failure of bearings and seals of pumps, as well as destruction of measuring devices.

7.2. Wrong Type of Check Valve for Application

Explanation: There are many types of check valves (pop, disc, rotary, lifting, spring, non-impact). Each of them has its optimal application conditions. For example, a standard cotton check valve (Swing Check Valve) is effective for low flow rates and large diameters where pressure drop must be minimal. However, its disc has a large stroke, which results in slow closing and makes it very vulnerable to water hammer in systems with rapid flow changes or high fluid inertia.

Spring Loaded Check Valves, especially axial (Axial Check Valve) or lift check valves (Lift Check Valve) with a short travel distance and a spring that actively closes the disc, greatly reduce the risk of water hammer because they react more quickly and close before the backflow gains significant velocity.

Confirmation: Comparison of installed valve type with manufacturer's recommendations for specific operating conditions (flow rate, pump stop time, pipe length). Typical of systems with frequent pump start/stops, the use of a standard poppet valve is a direct indicator of this root cause.

Consequences: Constant water hammer, premature wear of the valve and system, need for frequent repair or replacement.

7.3. Wear or Damage to Internal Valve Components

Explanation: Over time, due to erosion, cavitation, corrosion, or mechanical damage, the valve disc may not close completely, seize, or have excessive backlash. A worn valve seat loses its tightness, allowing fluid to flow backwards even in the "closed" position, causing disc "shaking" and frequent micro-hydro hammer. Damage to the spring in spring valves results in slow or incomplete closing, making them behave like cotton valves.

Confirmation: Valve disassembly and a thorough visual inspection of the internals. Search for such defects as:

• Traces of erosion or cavitation on the disc and saddle.
• Deformation or distortion of the disc.
• Axle / hinge wear or damage.
• Weakening or destruction of the spring.
• The presence of foreign objects preventing complete closure.

Consequences: Constant noise, vibration, energy losses due to backflow, damage to equipment due to water hammer, reduced system life.

7.4. Malfunction of Damper or Controlled Closing System

Explanation: Some check valves (especially large diameter ones) are equipped with hydraulic or pneumatic dampers to ensure smooth, controlled closing. This allows the disc to close slowly in the final stages of travel, preventing sudden flow blockage and quenching of water hammer energy. A malfunction of the damper (for example, leakage of working fluid, clogging, damage to the control elements) leads to the loss of this function, and the valve begins to close freely, like an uncontrolled cotton valve.

Confirmation: Visual inspection of the damper for leaks, blockages or mechanical damage. Checking the operation of the damper manually (if possible) or by observing the valve closing time. For hydraulic dampers – checking the level and condition of the working fluid.

Effects: The valve loses its ability to close smoothly, resulting in intense water hammer and all the associated damage described above.

7.5. Resonance of the System

Explanation: In rare cases, water hammer can be amplified or triggered by resonance, when the frequency of oscillations caused by the closing of the valve coincides with one of the natural frequencies of oscillations of the pipeline. This results in a significant increase in pressure and vibration amplitude, even if the initial impulse was relatively small.

Confirmation: Complex analysis requiring frequency analysis of peak pressures and vibration (using a vibroanalyzer). Comparison of the dominant frequencies of water hammer with the estimated natural frequencies of the pipeline.

Effects: Catastrophic destruction that is difficult to predict and localize, as the energy of the water hammer is multiplied many times over.

8. Step-by-Step Troubleshooting Procedures

After identifying the root cause, the following steps must be taken to eliminate water hammer:

8.1. Replacement of the Check Valve with the Appropriate Type

Step 1:  LOCKOUT / TAG OUT (LOTO). Isolate the piping section, depressurize, and drain the fluid according to safety procedures.

Step 2: Remove the existing check valve.

Step 3: Select a new check valve based on an analysis of transients in the system. Recommended types to prevent water hammer:

• No-Slam/Silent Check Valves: Quick spring closing, minimal disc travel. Effective for small and medium diameters.
• Hydraulic Damper Check Valves (Dashpot Check Valves): Provide controlled closing, especially for large diameters and high flow rates. Adjustable closing time.
• Axial Flow Check Valves (Axial Flow Check Valves): The spring and the aerodynamic/hydrodynamic shape of the disc ensure very fast closing.

Step 4: Install the new valve in the correct direction of flow (arrow on body). Use new gaskets and bolts. The tightening torque of the flange bolts must comply with the standards (for example, EN 1591-1 for flange connections).

Step 5: Start the system slowly, checking for pressure, flow, and absence of unusual noises.

8.2. Adjusting or Installing a Hydraulic/Pneumatic Damper

Step 1: BLOCK / TAG OUT (LOTO). Isolate the section of piping, depressurize and drain the fluid.

Step 2 (for existing damper): Check the level and condition of the working fluid (oil). Replace fluid if contaminated. Check the closing time adjustment settings. Clean the damper channels from blockages.

Step 3 (to install a new one): Install the damper on the existing check valve (if it supports this option) or replace the valve with a model with an integrated damper.

Step 4: Adjust the damper closing time. Initial values:

• For valves DN < 200 mm: closing time 0.5 - 1.0 seconds.
• For valves DN > 200 mm: closing time 1.0 - 3.0 seconds.

Perform test starts and stops of the pump, recording the pressure. The optimal closing time is the smallest time at which the pressure peaks do not exceed 1.25 times the working pressure.

8.3. Modernization of the Pump Management System

Step 1: Install soft starters or variable frequency drives (VFDs) for the pumps feeding fluid to the check valve.

Step 2: Configure the pump start and stop parameters:

• Acceleration time: 10-30 seconds.
• Deceleration time: 20-60 seconds.

Step 3: Perform test starts/stops while monitoring system pressure. The goal is to provide a gradual decrease in flow rate before the valve closes, minimizing inertial shock.

8.4. Repair or Replacement of Valve Components

Step 1: BLOCK / TAG OUT (LOTO). Isolate the section of piping, depressurize and drain the fluid.

Step 2: Remove the valve and disassemble it.

Step 3: Replace damaged or worn components (disc, saddle, stem, spring) with genuine UNITEC spare parts. Make sure all tolerances and clearances are in accordance with the manufacturer's specifications.

Step 4: Assemble the valve, ensuring the disc is properly centered and moves freely without jamming.

Step 5: Start the system slowly and test its operation.

8.5. Changes in the Pipeline Configuration

This method is used in extreme cases or as an additional means:

• Installation of air chambers or hydraulic accumulators: They absorb the energy of peak pressures, reducing the amplitude of water hammer. Place as close as possible to the source of water hammer.
• Bypass lines with control valves: Allows for controlled release of pressure or to maintain minimum flow, preventing total blockage.
• Changing the diameter or length of the pipeline: Can change the natural frequencies of the system and the speed of wave propagation, but is an expensive and complex solution.

9. Precautions

To prevent the re-occurrence of a non-return valve water hammer, it is necessary to implement a comprehensive prevention strategy:

10. Spare Parts and Components

Quality replacement parts are critical to effectively eliminate water hammer and ensure long-term system reliability. UNITEC-D GmbH offers a wide range of components that meet high quality standards.

To order quality spare parts and components certified by CE and UkrSEPRO, visit our electronic catalog UNITEC. Our specialists will help you choose the best solutions.

11. Links

• DSTU EN 12266-1:2018 Industrial pipeline fittings. Valve Testing (EN 12266-1:2012, IDT).
• ISO 4126-1:2013 Safety valves — Part 1: General requirements.
• ISO 10816-3:2009 Mechanical vibration — Evaluation of machine vibration by measurements on non-rotating parts — Part 3: Industrial machines with nominal power above 15 kW and nominal speeds between 120 r/min and 15,000 r/min when measured in situ.
• Operation and maintenance manuals from pump equipment and piping manufacturers (OEM).
• UNITEC: Internal technical manuals for the selection and operation of check valves.