Maintenance Guides 1 min read

Elimination of Water Hammer in Check Valves: Diagnosis, Analysis of Closing Speed ​​and Selection of Dampers

Technical analysis: Troubleshooting check valve water hammer: slam analysis, closing speed diagnosis, damper selection,

1. Description of the Problem and Scope of Application

Water hammer caused by improperly functioning check valves is a critical problem in industrial piping systems that can cause serious equipment damage, downtime, and endanger personnel safety. This manual focuses on the diagnosis, identification of root causes, and elimination of water hammers caused by sudden closing or opening of check valves.

Equipment covered: Pumping stations, main and process pipelines, water supply, heating and cooling systems, oil and gas pipelines, chemical plants where check valves are used to prevent backflow of liquid. The main types of valves considered are lifting, rotary and quiet (axial).

Severity Classification:

  • Critical: Destruction of pipelines, pumps, fittings; leakage of dangerous substances; threat to life and health of personnel. Requires immediate intervention.
  • Significant: Frequent triggering of defenses; damage to valve seals; intense vibration and noise; accelerated wear of equipment. Requires planned repair or modernization.
  • Minor: Intermittent noise or slight vibration. Requires monitoring and inclusion in a preventive maintenance plan.

2. Precautions

ALWAYS FOLLOW FACILITY SAFETY PROCEDURES BEFORE BEGINNING ANY DIAGNOSTIC OR REPAIR WORK ON A SYSTEM WITH PIPING SUBJECT TO WATERSHED. FAILURE TO COMPLY COULD RESULT IN SERIOUS INJURY OR DEATH.

  • LOCKOUT/TAGOUT (LOTO): Before any intervention in the piping system, ensure that the energy sources (electrical, hydraulic, pneumatic) are isolated and the equipment is locked out and tagged according to DSTU EN 10301:2006 standards.
  • PERSONAL PROTECTIVE EQUIPMENT (PPE): Use appropriate PPE: safety glasses (DSTU EN 166:2017), protective gloves, protective clothing, protective shoes (DSTU EN ISO 20345:2019), hearing protection devices (DSTU EN 352-1:2017) when working in high noise areas.
  • STORED ENERGY: Ensure that all stored energy (fluid pressure, spring tension, electrical charge on capacitors) in the system is completely released or safely controlled before disassembling any components.
  • GASES AND LIQUIDS UNDER PRESSURE: Before opening any flange connection or drain valve, ensure that the piping section is completely de-energized, cooled and depressurized to atmospheric pressure. Follow procedures for handling hazardous substances, if present in the system.

3. Necessary Diagnostic Tools

Specialized equipment is required for effective water hammer diagnostics. Below is a list of recommended tools:

Tool Specification / Model Range of Measurements Purpose
High-speed pressure sensor (piezoresistive) Kistler 211B5, Kulite XTL-190M 0-100 bar; frequency 0-10 kHz Registration of peak pressure values and rapid drops indicating water hammer.
Portable vibroanalyzer with accelerometer Vibrometer 2000, Brüel & Kjær Type 2250 10 Hz - 10 kHz; sensitivity 100 mV/g Vibration detection of the valve body and adjacent piping indicating shock and structural response. ISO 10816.
Ultrasonic flowmeter (external application) Clamp-on Ultrasonic Flowmeter (pr. FLUXUS F601) 0.1-20 m/s Non-contact measurement of fluid flow rate, especially the backflow rate before closing the valve.
High-speed video camera Phantom v711, GoPro Hero (special mode) 200-1000 frames/s Visual registration of the dynamics of the closing of the non-return valve, the movement of the spool, and vibration.
Thermal imager Flir T-series, Testo 883 -20°C to +350°C; accuracy ±2°C Detection of local overheating (friction) or hypothermia (cavitation) in the valve area.
Multimeter (with current measurement function) Fluke 87V, Kyoritsu 1021R Voltage up to 1000 V; Current up to 10 A (post/shift) Diagnostics of electrical components (for example, solenoids, actuators) that control valve operation.
Portable oscilloscope Tektronix TBS1052B, Picoscope 2205A Bandwidth from 50 MHz; 2 channels Visualization of electrical signals from pressure, vibration, valve opening/closing sensors.

4. Initial Evaluation Checklist

Перед початком детальної діагностики проведіть початкову оцінку, зібравши базову інформацію про систему та симптоми. This will help narrow down the potential causes.

Item Rating What to Observe / Record Meaning
Frequency and time of water hammer occurrence Is water hammer permanent, periodic? Is it related to starting/stopping the pump, changing the load? Record the exact time, duration, frequency
Pump operation mode Power, suction/discharge pressure, engine speed. Normal, reduced, increased. Does it work within the operating point?
Check valve type and size Manufacturer, model, nominal diameter (DN), pressure (PN). Check whether the valve type is suitable for the operating conditions.
History of alarms and faults SCADA logs, ACS systems. Record previous incidents related to pressure, vibration or pump operation.
Pipeline configuration Length, diameter, material, presence of taps, risers, compensators, branches. Visual inspection for lack of fasteners, sagging.
Availability and serviceability of damping devices Hydraulic accumulators, dampers, air caps. Check the gas pressure in the hydraulic accumulators, the presence of leaks.
Temperature and liquid properties Temperature, viscosity, density. Fluid parameters affect sound speed and kinetic energy.
Visual inspection of the valve The presence of external damage, leaks, traces of vibration. Signs of wear, corrosion, foreign objects.

5. Systematic Diagnostic Block Diagram

Follow this sequence to locate the root cause of the water hammer.

  1. Symptom: Intense, sharp knock/thump and vibration in the check valve area after the pump is stopped.
    1. Diagnostic step: Visual inspection and auscultation of the valve while the pump is stopped.
      • If: A metallic impact is clearly heard.
        1. Probable cause: Rapid (abrupt) closing of the valve spool under the effect of backflow.
          1. Diagnosis: Measure the valve closing time using a high-speed camera and an ultrasonic flow meter.
            • Expected result: The closing time is less than 0.2-0.5 seconds; the speed of the reverse flow is more than 1 m/s.
            • Check: Valve spring stiffness (if applicable) or spool weight.
              • If: The spring is too stiff or the spool is too light for the given backflow.
              • Root cause: Incorrect selection of valve or its components for system dynamics.
            • Check: Damper presence and serviceability (eg hydraulic damper in rotary valves).
              • If: The damper is faulty (fluid leakage, blocked channels) or missing.
              • Root cause: Damage or missing damping device.
  2. Symptom: Continuous vibration, hum or cavitation noise in the pipeline after stopping the pump, without a sudden impact of the valve. Pump pressure drop after shutdown, then recovery.
    1. Diagnostic step: Measure the pressure downstream of the pump and before the check valve with a high-speed pressure sensor during shutdown.
      • If: The pressure drops to zero or negative and then increases sharply.
      • Probable Cause: The check valve is closing too slowly, allowing significant backflow to develop.
        1. Diagnosis: Measure valve closing time and backflow rate.
          • Expected result: Closing time over 1.0-2.0 seconds; the speed of the reverse flow is more than 1.5 m/s.
          • Check: For foreign objects or dirt in the valve mechanism.
            • If: Mechanical interference is detected.
            • Root cause: Clogged valve.
          • Check: Wear or damage to the internal moving parts of the valve (spool, stem).
            • If: Backlash, wear, corrosion is detected.
            • Root cause: Mechanical valve wear.
          • Check: Serviceability and stiffness of the spring (if any).
            • If: The spring is loose or broken.
            • Root Cause: Valve spring failure.
  3. Symptom: Continuous or intermittent vibration and noise not directly related to pump start/stop.
    1. Diagnostic step: Measure valve body and pipeline vibration with a vibration analyzer.
      • If: High vibration levels (>7.1 mm/s RMS for nominal conditions, ISO 10816-3).
        1. Probable cause: The valve spool is in an unstable position (flutter) or excessive flow rate through the valve.
          1. Diagnosis: Measure the flow rate through the valve with an ultrasonic flow meter.
            • Expected Result: Flow velocity is higher than recommended for this type of valve (for example, more than 3 m/s for most rotary valves).
            • Check: Correspondence of the valve size (DN) to the nominal diameter of the pipeline and the working flow.
              • If: The valve is too small for the flow volume.
              • Root cause: Incorrect selection of valve size.
  4. Symptom: Regular damage to valve seals, worn spool or seat, frequent leaks.
    1. Diagnostic step: Visual inspection of valve internals during routine maintenance.
      • If: Mechanical damage, erosion, cavitation traces are detected.
        1. Probable cause: Chronic water hammer or flutter resulting in cyclic loads.
          1. Diagnosis: Carry out a complete analysis of the system according to points 1 and 2 of this section.
          2. Expected result: Confirmation of one of the above reasons.
          3. Root Cause: Any of the above that was not remedied in a timely manner.

6. Matrix "Symptom - Probable Cause"

This table will help you quickly correlate observed symptoms with the most likely root causes and diagnostic measures.

Symptom Probable Causes (by probability) Diagnostic Test Expected Result if Cause Confirmed
A sharp metallic knock when closing the valve after stopping the pump.
  1. Quick closing of the valve (too stiff spring, light spool).
  2. Absence or malfunction of the damper.
  3. Incorrect type of valve (for example, a rotary valve in a vertical pipeline).
  1. Measurement of shutter time (high speed camera).
  2. Visual inspection of the damper, checking the fluid level.
  3. Assessment of valve compliance under operating conditions.
  1. Closing time < 0.3 s.
  2. Leakage of damping fluid, clogging.
  3. Non-compliance with the manufacturer's recommendations.
Long hum, vibration, cavitation noise after stopping the pump.
  1. Slow valve closing (weakened spring, contamination, wear).
  2. Excessive backflow.
  3. Insufficient flow rate in normal mode (valve does not fully open).
  1. Measurement of closing time and reverse flow (ultrasonic flow meter).
  2. Dismantling and inspection of the internal parts of the valve.
  3. Measuring the pressure drop across the valve during operation.
  1. Closing time > 1.5 s; return flow > 1.5 m/s.
  2. Clogging, saddle wear, weakened spring.
  3. A high pressure drop indicates a partially closed valve.
Constant vibration of the valve and pipeline during normal operation.
  1. Spool flutter (instability at partial opening).
  2. Flow rate through valve too high (incorrect size).
  3. Clogging that prevents full opening.
  1. Vibration measurement (vibration analyzer).
  2. Flow rate measurement (ultrasonic flowmeter).
  3. Visual inspection, endoscopy (if possible).
  1. Vibration level > 7.1 mm/s RMS.
  2. Flow speed > 3 m/s.
  3. Detection of foreign objects.
Frequent leaks, damage to the seals, erosion of the inner surfaces of the valve.
  1. Chronic hydrocephalus (any of the above reasons).
  2. Cavitation due to suboptimal system design.
  1. Comprehensive analysis of system dynamics.
  2. Analysis of materials and chemical composition of liquid.
  1. Confirmation of water hammer.
  2. Signs of cavitation destruction.

7. Root Cause Analysis for Each Malfunction

7.1. Quick (Abrupt) Closing of the Check Valve

Explanation: This type of water hammer occurs when the check valve spool closes too quickly after a sudden stop to direct flow (such as a pump emergency stop). Fluid moving by inertia creates a reverse flow that stops abruptly against the closed valve spool. This creates a high-pressure shock wave that propagates through the pipeline.

How to confirm: Measure the valve closing time (should be in the range of 0.3-1.0 seconds for most applications, depending on DN and PN) using a high-speed video camera synchronized with pressure logging. A sharp increase in pressure (peaks 2-5 times higher than the working pressure) immediately after closing the valve confirms this scenario. Analysis of the oscillogram of the pressure sensor will show a short-term, high-amplitude pulse.

Damage:

  • Deformation and destruction of pipelines, flange connections.
  • Damage to internal components of the valve (spool, seat, spring).
  • Detachment of fasteners and supports of the pipeline.
  • Breakdown of measuring devices, pumps.
  • Creation of a dangerous situation for personnel due to leakage of liquid under pressure.

7.2. Slow Closing of the Check Valve

Explanation: This reason is the opposite of the previous one. If the non-return valve closes too slowly, a significant volume of liquid has time to move in the reverse direction. When the valve finally closes, this backflow also stops abruptly, creating a water hammer. Also, the presence of backflow can cause cavitation in the valve and pump area, especially at low pressures.

How to confirm: Measure valve closing time (more than 1.5-2.0 seconds is a sign of slow closing) and backflow rate. An ultrasonic flow meter can detect significant backflow before the valve is fully closed. At the same time, the pressure peaks may be lower than in the case of sudden closure, but the water hammer may have a longer and fluctuating nature.

Damage:

  • Erosion and cavitation destruction of the valve seat and spool.
  • Reverse rotation and damage to the pump impeller.
  • Wear of sealing surfaces, which leads to constant leaks.
  • Decreasing system efficiency due to constant backflow.

7.3. Incorrect Selection of Valve Type and Size (Flutter)

Explanation: An incorrectly sized or typed valve can operate in an unstable mode known as flutter. This occurs when the valve does not fully open at rated flow or its spool oscillates under the flow, creating constant micro-bumps against the seat. For example, a rotary valve in a vertical pipeline where gravity cannot turn the spool quickly, or a valve selected with excessive DN margin operating at low flow rates.

How to confirm: Constant vibration and noise of the valve during normal operation, recorded by a vibration analyzer (vibration level exceeds 7.1 mm/s RMS, category "Unacceptable" according to ISO 10816-3). A pressure drop across the valve that is higher than the calculated one may indicate its partial opening. A high-speed camera can show spool oscillation.

Damage:

  • Accelerated wear of moving parts of the valve, seat and seals.
  • Metal fatigue of the valve body and adjacent sections of the pipeline.
  • Damage to the rod, axle or other internal components.
  • Decrease in throughput and increase in energy consumption.

8. Step-by-Step Troubleshooting Procedures

8.1. Elimination of Hydroshock from Quick Close

  1. Hydraulic Damper Installation/Adjustment:
    • Application: For rotary check valves. Install a hydraulic damper or adjust the existing one.
    • Action: Increase the valve closing time to 0.5-1.0 seconds by adjusting the speed of liquid displacement from the damper. Start with the minimum speed, gradually increasing it until you reach the optimal closing time without water hammer.
    • Check: Start and stop the pump, monitoring pressure and vibration. The peak pressure values ​​after closing the valve should not be higher than 1.2-1.5 of the working pressure.
  2. Use of Valves with Controlled Closure:
    • Application: For systems with frequent stops and high risk of water hammer.
    • Action: Replace the existing check valve with a specialized one, such as a silent axial check valve with a damping spring or a piston valve with a hydraulic damper.
    • Check: Run a system test. Follow the manufacturer's recommendations for installation and setup.
  3. Change Spring Characteristics (for lifting valves):
    • Application: If the spring is too stiff.
    • Дія: Встановіть пружину з меншою жорсткістю, щоб збільшити час закриття. Follow the manufacturer's specifications.
    • Check: Pressure and vibration monitoring.

8.2. Eliminates Hydroshock from Slow Close

  1. Valve Cleaning and Maintenance:
    • Application: When dirt or mechanical obstacles are detected.
    • Action: Dismantle the valve, thoroughly clean all internal surfaces, seat, spool. Check for corrosion or build-up. Replace worn seals.
    • Check: After installation, check for tightness and functionality.
  2. Replacement of Worn Components:
    • Application: When detecting wear of the spool, seat, rod or weakened spring.
    • Action: Replace damaged or worn parts with original or equivalent parts conforming to standards EN 12516-1, EN 13709.
    • Check: Check the closing force and response speed of the valve.
  3. Increasing Spring Stiffness (for lift valves):
    • Application: If the spring is weak or too soft.
    • Action: Install a stiffer spring to speed up the spool closing.
    • Check: Monitoring of closing time and absence of backflow.

8.3. Elimination of Incorrect Valve Selection (Flutter)

  1. Valve Size Check and Correction:
    • Application: If the valve is too large or small for the operating conditions.
    • Action: Perform a hydraulic calculation of the system. Select a non-return valve with a nominal diameter (DN) that will provide minimum resistance at maximum flow and quick closing at reverse flow. For most non-return valves, the recommended minimum flow velocity for full opening is 1.5-2.0 m/s.
    • Check: After replacing the valve, measure the pressure drop across the valve and the vibration during operation.
  2. Зміна Типу Клапана:
    • Застосування: Якщо тип клапана не відповідає умовам (наприклад, поворотний клапан у вертикальному трубопроводі).
    • Action: Replace the valve with a more suitable type, such as a silent axial or dual disc rotary valve.
    • Check: System testing.

9. Preventive Measures

Preventing water hammers is much more effective and economical than eliminating their consequences.

The root cause Prevention Strategy Monitoring method Recommended Interval
Quick closing of the valve
  • Using check valves with dampers or controlled closing.
  • Optimization of pump stop time (soft stop).
  • Regular control of pressure and vibration (online monitoring).
  • Акустичний моніторинг (слухання).
 Monthly / After each pump stop
Slow closing of the valve
  • Regular maintenance, cleaning and lubrication of valves.
  • Installation of filters to prevent pollution.
  • Visual overview.
  • Pressure drop measurement.
  • Endoscopy.
 Quarterly / During scheduled maintenance
Incorrect valve selection (flutter)
  • Thorough hydraulic calculation of the system during design.
  • Selection of the valve according to the actual operating points (flow rate, pressure).
  • Vibration monitoring.
  • Analysis of hydraulic characteristics (pressure, flow).
 After installation / Every 6 months
General wear, corrosion
  • Use of valves made of materials resistant to aggressive environments.
  • Adherence to schedules for replacement of consumable parts.
  • Visual overview.
  • Service life analysis.
 During each scheduled maintenance

10. Spare Parts and Components

For quick and efficient repairs, it is important to have the necessary spare parts on hand. UNITEC-D GmbH offers a wide range of components for check valves that meet CE and UkrSEPRO standards.

Description Details Specification When to Replace Category UNITEC
Repair kit for check valve Includes seals (NBR, EPDM, Viton), springs, bushings. According to DIN EN ISO 10497:2010. When leaks are detected, reduced functionality, during scheduled maintenance. Reinforced seals
Springs for lifting valves Material: stainless steel (AISI 304/316). According to DIN EN 13917. In case of weakening, breakage or to adjust the closing time. Valve springs
Check Valve Spool/Disc Material: high strength cast iron, stainless steel, bronze. According to DIN EN 1983. In case of erosion, cavitation destruction, deformation. Valve components
Hydraulic damper assembly According to OEM specifications. In case of leakage of damping fluid, clogging of channels, impossibility of adjustment. Dampers and actuators
Full check valve (spare) Тип: безшумний осьовий, подвійно-дисковий поворотний. DN, PN according to the system specification. Body material: GJL-250 (EN 1561), GP240GH (EN 10213). If it is impossible to repair the existing one, if it is necessary to change the type of valve. Check valves

Find the parts you need in our e-catalogue: www.unitecd.com/e-catalog/

11. Links

  • DSTU EN 10301:2006 (EN 10301:2001, IDT) "Pipelines. Pumping and compressor stations. General safety requirements".
  • DSTU EN 166:2017 (EN 166:2001, IDT) "Means of individual eye protection. Technical requirements".
  • DSTU EN ISO 20345:2019 (EN ISO 20345:2011, IDT; ISO 20345:2011, IDT) "Means of personal protection. Shoes are safe."
  • DSTU EN 352-1:2017 (EN 352-1:2002, IDT) "Means of individual protection of hearing organs. General requirements. Part 1. Anti-noise headphones".
  • 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."
  • EN 12516-1:2014 "Industrial pipeline fittings. Calculation, design and testing methods. Part 1: Calculation method for steel reinforcement cases".
  • EN 13709:2002 "Industrial pipeline fittings. Steel latches".
  • DIN EN ISO 10497:2010 "Reinforcement testing. Test by external fire".
  • DIN EN 13917:2004 "Springs. Terms and definitions".
  • DIN EN 1983:2013 "Industrial pipeline fittings. Steel non-return valves".
  • Check valve manufacturers' manuals (eg ARI-Armaturen, KSB, Kitz).

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