Diagnostic Guide: Troubleshooting Hydraulic Shock in Check Valves

1. Description of the Problem and Scope of Application

Hydraulic shock in pipeline systems caused by rapid closing of a check valve, known as "slap" or "slam shut", is a critical operational problem. This phenomenon is characterized by a sharp increase in pressure, which occurs as a result of a sudden stop or change in the direction of the flow of liquid. The kinetic energy of the moving fluid is converted into pressure energy, creating shock waves that propagate through the pipeline. This can lead to serious damage: destruction of pipelines, flange connections, pumping equipment, measuring devices and, in fact, the check valve itself. Typical symptoms include loud noise, vibration, leakage in connections and frequent failures of system components.

This manual is intended for technical personnel, reliability engineers and heads of maintenance departments at production enterprises in Ukraine. It covers the diagnosis and repair of hydraulic shock caused by check valves in water supply systems, oil and gas pipelines, refrigeration systems and other fluid transport systems. Severity classification: critical (possible pipeline destruction, production shutdown), significant (damage to valves/pumps, leaks, need for emergency repairs), minor (constant noise, increased wear without immediate threat).

2. Security measures

SAFETY WARNING:

• Before performing any diagnostic or repair work on a piping system that is potentially subject to hydraulic shock, MUST isolate the affected section and perform a Lockout and Tagout (LOTO) procedure in accordance with DSTU EN ISO 14118:2018.
• Make sure there is no pressure in the system and drain the fluid if necessary. Be aware of stored energy in valve springs and damping systems.
• Use personal protective equipment (PPE): safety glasses/shields, gloves, helmets, safety shoes.
• Be careful when working with hot or aggressive liquids. Check the temperature and chemical composition of the liquid before starting work.
• When measuring vibration or noise generated during hydraulic shock, keep a safe distance and avoid direct contact with vibrating components.

3. Necessary Diagnostic Tools

For effective diagnosis of the causes of hydraulic shock, a set of specialized tools is required:

4. Initial Assessment Checklist

Before starting a detailed diagnosis, it is necessary to collect as much information as possible about the system and its operating conditions:

5. Systematic Diagnostic Block Diagram

This section offers a logical sequence of steps to identify the root cause of hydraulic shock:

1. Symptom: A loud "cluttering" sound and/or vibration when the check valve closes.
   • Initial evaluation:
     1. Check the alarm log and SCADA/ACC data.
     2. Inspect the valve and adjacent piping for visible damage or leaks.
     3. Determine the exact time and conditions of the impact (for example, when the pump stops, when the shut-off valve is activated).
   • Diagnostics: Analyze valve closing dynamics and hydraulic conditions.
     1. Measure peak pressures: Install a pressure recorder just before and after the check valve.
        • Expected result: Pressure peaks exceeding the operating pressure of the system by 1.5-2.0 times or absolute values ​​above 20 bar may indicate hydraulic shock.
          (Normal pressure fluctuations should not exceed 10% of the working pressure.)
     2. Measure vibration: Use a vibration analyzer on the valve body and adjacent piping.
        • Expected result: Significant vibration peaks (more than 15 mm/s RMS) at the moment of impact, especially at high frequencies (above 100 Hz), indicate rapid mechanical collision of internal elements.
          (According to EN ISO 10816-1, vibration of equipment in good condition is usually below 4.5 mm/s RMS.)
     3. Estimate the flow rate and its variation: Use an ultrasonic flowmeter.
        • Expected result: High flow speed (over 3 m/s) and its rapid fall or change of direction.
   • IF the measurement result confirms the hydraulic shock:
   1. Checking check valve type and system compatibility:
      • IF swing type valve without damper or spring:
        • Probable cause: The valve closes too slowly, allowing a significant amount of backflow to build up inertia, and then closes abruptly under the action of this flow.
        • Diagnosis: Visual inspection, analysis of valve documentation.
        • Go to: 7.1 Wrong Selection of Check Valve Type.
      • IF spring type valve, but the spring is too weak or damaged:
        • Probable cause: Insufficient spring force does not close quickly before the flow direction changes.
        • Diagnostics: Valve disassembly (after LOTO), visual inspection of the spring for corrosion, deformation, spring stiffness measurement (if possible).
        • Go to: 7.3 Wear or Damage to Valve Components.
      • IF is an axial or two-leaf damper type valve, but the damper is faulty or incorrectly adjusted:
        • Probable cause: The damper is not damping the closing energy properly.
        • Diagnosis: Visual inspection of the damper for leaks, damage, check of the damping fluid level, adjustments.
        • Go to: 7.4 Malfunction of Damping Device.
   2. Analysis of system hydraulic conditions:
      • IF rapid shutdown of pump or other pressure sources:
        • Probable cause: A sudden stop of flow creates a vacuum wave followed by a backflow wave that causes the valve to close rapidly.
        • Diagnostics: Analysis of SCADA logs, pump current oscillogram, timing of events.
        • Go to: 7.2 Excessive Backflow Rate.
      • IF air or gas in the system:
        • Probable cause: Air plugs can cause uneven flow and sudden acceleration/deceleration, as well as dampen the initial pressure wave, which then leads to a stronger compression shock.
        • Diagnosis: Checking the presence of air valves, their efficiency, visual inspection of the system for the presence of areas with possible accumulation of air.
        • Go to: 7.5 Presence of Air Inclusions in the System.
      • IF significant pipeline length or high head:
        • Probable cause: Long pipelines have greater fluid inertia, which increases the effects of hydraulic shock. High pressure increases the potential energy of the impact.
        • Diagnostics: Analysis of project documentation of the system, modeling of hydraulic transients.
        • Go to: 7.6 Inadequate Hydraulic System Design.

6. Matrix of Malfunctions and Causes

This chart will help you quickly identify likely causes of hydraulic shock based on observed symptoms and perform the appropriate diagnostic tests.

7. Analysis of the Root Causes of Each Malfunction

7.1. Incorrect Selection of Check Valve Type

Explanation: Check valves are of different types (rotary, lifting, two-leaf, seed, ball), each of which has its own closing characteristics. Non-damped check valves, especially large diameters, have a significant gate mass and can close relatively slowly, allowing significant backflow to build up to full closure. When this backflow is suddenly stopped by a valve, an intense hydraulic shock occurs. The same applies to lifting valves in vertical pipelines, where gravity does not contribute to quick closing.

How to confirm: Analysis of the design documentation of the system and the specification of the installed valve. Simulation of hydraulic transients will show whether the selected valve type meets the dynamic conditions of the system (especially when the pump is stopped). A visual inspection and, if necessary, disassembly of the valve will allow to assess its design features (presence of springs, dampers).

Consequences: If not eliminated, this will lead to constant hydraulic shocks, causing fatigue of pipeline materials, flanges, pumps. This shortens the life of equipment, increases maintenance costs and increases the risk of sudden system failure, which can lead to production losses and environmental accidents.

7.2. Excessive Backflow Rate

Explanation: When the pump is suddenly turned off, the flow of liquid in the pipeline does not stop immediately. By inertia, it continues to move forward, creating a zone of reduced pressure (or vacuum) behind the pump, and then reverses direction. The velocity of this backflow tending to close the check valve can be very high, especially in long pipelines or at high operating flow rates. The higher the velocity of the backflow, the stronger the blow when the valve closes.

How to confirm: Detailed analysis of pressure recorder and ultrasonic flowmeter data during pump test shutdowns. Simulation of transient processes (transients) using specialized software (eg AFT Impulse, Bentley HAMMER) allows accurate prediction of backflow rates and peak pressures. According to EN ISO 10052, the maximum flow velocity in the pipelines of pumping systems should not exceed 3 m/s to minimize the risk of hydraulic shock.

Consequences: Destruction of the valve disc/valve, damage to internal components, deformation of the body. Prolonged water hammer action causes secondary damage such as depressurization of flanges, damage to seals and pipeline supports.

7.3. Wear or Damage to Valve Components

Explanation: Over time, springs in spring check valves can lose stiffness due to material fatigue or corrosion. Stems can jam, saddles and discs can wear due to abrasive particles in the liquid or cavitation. Any of these damages prevent the valve from closing quickly and smoothly, increasing the likelihood of hydraulic shock. For example, jamming of the valve stem of a rotary valve can cause it to not fully close and then suddenly slam shut.

How to confirm: Disassembly and visual inspection of the internal parts of the valve (seat, disk, rod, spring, damper). Checking the spring for deformation and corrosion. Measure spring stiffness, if possible. Assessment of the condition of sealing surfaces. Backlash measurement.

Consequences: Constant "rattling" of the valve, leaks, increased power consumption of the pumps due to additional resistance, complete failure of the valve, which can lead to uncontrolled backflow and damage to the pumps.

7.4. Malfunction of Damping Device

Explanation: Dampers (hydraulic or pneumatic) used in non-return valves (e.g. double-leaf or butterfly valves) are designed to controllably decelerate the closing of the valve, thereby preventing sudden shock. Damper malfunctions such as fluid leakage, clogging of channels, piston damage or incorrect adjustment lead to loss of damping function. The valve begins to close uncontrollably, causing hydraulic shock.

How to confirm: Visual inspection of the damper for leaks. Checking the level of the working fluid (if provided by the design). Checking damping settings (closing speed). If necessary, dismantling and disassembling the damper to check internal components (seals, springs, valves).

Consequences: Loss of smooth closing, increased hydraulic shock, damage to the damper and valve, which can ultimately lead to the destruction of the pipeline and related equipment.

8. Step-by-Step Troubleshooting Procedures

8.1. Replacement or Modernization of the Check Valve

1. WARNING: Isolate the pipeline section and perform the Lockout and Tagout (LOTO) procedure according to DSTU EN ISO 14118:2018. Декомпресуйте систему.
2. Виконайте аналіз навантаження на систему для визначення оптимального типу та розміру клапана. Врахуйте параметри: діаметр трубопроводу, максимальну та мінімальну витрату, робочий тиск, властивості рідини, довжину трубопроводу. For systems with rapid flow changes (e.g. after pumps) it is recommended to use spring-loaded seat valves or two-leaf valves with dampers.
3. Встановіть відповідний клапан:
   • Для рідин: Пружинні осівні зворотні клапани (EN 14341) або двостулкові клапани з регульованими демпферами, які закриваються до зміни напрямку потоку. For DN 100-200 mm valves, the spring must ensure closing of the gate in no more than 0.2 seconds.
   • Для газів: Клапани з низькою інерцією затвора, наприклад, осівні дискові, що мінімізують час закриття.
4. Torque the flange bolts to EN 1591-1:2013 using a calibrated torque wrench. Ensure even load distribution.
5. Після монтажу повільно заповніть систему та перевірте на герметичність згідно з DSTU EN 12266-1:2015.
6. Проведіть тестовий пуск/зупинку насоса та повторіть вимірювання тиску та вібрації. Pressure peaks should not exceed 1.15 P_working. Vibration should be within normal limits.

8.2. Optimization of Pumping Station Operation Modes

1. ПОПЕРЕДЖЕННЯ: Роботи з електрообладнанням виконувати лише кваліфікованим персоналом з дотриманням правил електробезпеки згідно з ПУЕ.
2. Install or configure soft starters or variable frequency drives (VFDs) on pumps.
   • Parameter: The deceleration time of the pump when stopped should be increased to 10-30 seconds (depending on the inertia of the system and the length of the pipeline) to ensure a smooth decrease in flow.
   • Verification: Recording of pressure dynamics and flow rate during pump stop.
3. The use of additional safety devices, such as surge relief valves, which are activated when the set pressure is exceeded and discharge part of the liquid from the system, extinguishing the shock wave. Adjust the actuation pressure to 1.25 P_operating.
4. Implement synchronized control of shut-off valves and pumps to avoid rapid closing of valves against high flow.

8.3. Installation of Additional means of extinguishing water hammers

1. WARNING: All welding and installation of pipelines must be performed in accordance with DSTU EN ISO 3834-2:2019 and safety rules.
2. Hydraulic accumulators/air chambers: Install pneumatic or hydropneumatic accumulators as close as possible to the check valve on the pump side. They absorb the energy of pressure peaks and compensate for pressure drops. Battery volume and charging pressure (usually 60-80% P_working) are calculated according to system parameters.
3. Air valves/pistons: Install automatic air valves at the upper points of the pipeline to release accumulated air and to admit air when a vacuum is created. This prevents the rupture of the liquid column and subsequent water hammer during the merger.
4. Compensators: Installation of compensators (rubber or bellows) can absorb part of the vibration and impact energy, protecting flange connections and supports.

9. Preventive Measures

10. Spare Parts and Components

Timely replacement of worn components is key to preventing hydraulic shock and ensuring reliable system operation. Always use original or certified analogues that comply with EN and ISO standards.

To order high-quality spare parts and components that meet European CE standards and Ukrainian UkrSEPRO certification, please refer to the UNITEC electronic catalog: https://www.unitecd.com/e-catalog/

11. Links

• DSTU EN ISO 14118:2018. Machine safety. Prevention of unexpected start.
• DSTU EN 12266-1:2015. Industrial pipeline fittings. Valve testing. Part 1: Pressure tests, functional tests and acceptance criteria.
• EN 1591-1:2013. Flanges and their connections. Calculation of flange connections with gaskets. Part 1: Calculation method.
• EN ISO 10816-1:2009. Mechanical vibration. Evaluation of machine vibration by measuring on non-rotating parts. Part 1: General guidelines.
• DSTU ISO 10052:2008. Pumps Pump units. General requirements for installation, operation and maintenance.
• EN 14341:2006. Industrial pipeline fittings. Check valves with a cap.
• DSTU EN ISO 3834-2:2019. Requirements for the quality of fusion welding of metallic materials. Part 2: Comprehensive quality requirements.
• IEC 60034-1:2017. Rotating electric machines. Part 1: Ratings and characteristics.