Elimination of hydraulic shock in check valves: diagnosis of slamming, analysis of closing speed and selection of dampers

1. Description of the problem and scope of application

Hydraulic hammer caused by check valves is a common and critical problem in industrial piping systems, which can lead to significant mechanical damage, equipment failure, and even catastrophic failure. This phenomenon occurs when the fluid flow in the pipeline suddenly changes direction and the check valve closes quickly, creating a sudden pressure jump (pressure pulse).

Symptoms of hydraulic shock:

• Characteristic noises: Sharp, loud bangs or "pops" from the side of the valve or adjacent sections of the pipeline.
• Pipeline vibration: Perceptible vibration or movement of pipes, especially when stopping pumps or making rapid changes in operation.
• Pressure fluctuations: Sharp and short-term jumps or drops in pressure recorded by manometers or pressure sensors.
• Damage to equipment: Destruction or damage to non-return valves (breakage of disc, rod, spring), leakage of flange connections, deformation or destruction of pipelines, damage to pumps and other fittings.

Affected equipment types:

This manual applies to all types of non-return valves (lift, rotary, inter-flange, ball, bi-valve, axial) in fluid pumping systems such as:

• Water supply and drainage systems.
• Oil and gas pipelines.
• Cooling and heating systems.
• Chemical and petrochemical industries.
• Energy installations.

Classification of severity:

• Critical: Immediate risk of pipeline destruction, leakage of hazardous substances, significant damage to pumps or other expensive equipment. Requires immediate shutdown and repair.
• Significant: Leaks, damage to individual valve components, increased wear leading to unplanned downtime.
• Minor: Intermittent noise and light vibration with no visible damage, but has the potential to progress to a significant or critical problem.

2. Precautions

  ATTENTION! Before starting any diagnostic or repair work related to piping systems where there is a risk of hydraulic shock, the following safety rules must be strictly observed:

• Lockout and Tagout (LOTO): Be sure to isolate and de-energize all sources of energy (electrical, hydraulic, pneumatic) for pumps and valves that control the flow in the area under investigation. Apply blocking and marking procedures in accordance with the company's internal standards and the requirements of DSTU OHSAS 18001 or ISO 45001.
• Personal Protective Equipment (PPE): Always wear appropriate PPE: safety glasses, hard hat, safety gloves, safety shoes, and ear protection (earplugs or headphones) due to the high noise level during water hammer.
• Energy storage: Remember the stored energy in pipelines (pressure, temperature). Make sure the system is fully decompressed and cooled to safe temperatures before disassembly.
• Hazardous liquids: When working with aggressive, toxic or flammable liquids, follow special safety procedures, use appropriate personal protective equipment and ensure adequate ventilation.
• Pipeline stability: Avoid being near unsupported sections of pipeline during potential hydraulic shock, as pipe movement can be unpredictable.

3. Necessary diagnostic tools

For effective diagnostics of hydraulic shock, specialized tools are required:

4. Initial evaluation checklist

Before starting a detailed diagnosis, it is necessary to collect initial data and conduct a visual inspection:

5. Systematic flow of diagnostics

1. Symptom detection of water hammer:
   1. Do you hear a loud "pop" or banging when the pump stops?
   2. Do you see vibration or movement of the pipeline?
   3. Does the manometer show sudden pressure jumps?
   4. If YES to any of the items: Go to step 2.
   5. If NO: Maybe the problem is not the check valve water hammer. Additionally, check for other sources of noise or vibration.
2. Hydraulic confirmation and data logging:
   1. Install high-speed pressure sensors directly before and after the check valve.
   2. Install vibration sensors on the valve and adjacent sections of the pipeline.
   3. Use a data acquisition (DAQ) system to simultaneously record pressure and vibration.
   4. Start and stop the pump, reproduce the conditions that cause water hammer.
   5. Analysis of data:
      1. Are the peak values ​​of pressure, which exceed the working pressure by 1.5-2 times, recorded? (Alarm threshold: P_peak > 1.5 * P_working).
      2. Are there high vibration peaks (>15 mm/s RMS) at the same time as the pressure peaks?
      3. If YES to both items: Hydraulic shock confirmed. Go to step 3.
      4. If NO: Perhaps the problem is mechanical damage to the valve or other elements without significant water hammer.
3. Estimating valve closing and flow reversal rates:
   1. Use an ultrasonic flow meter to measure fluid flow rates before and after the valve.
   2. Record the time from pump shut-off to full valve closure (visually, if possible, or using a position sensor).
   3. Analysis:
      1. Does reverse flow (negative velocity value) occur before the valve closes?
      2. Is the valve closing time very short (eg <0.1-0.5 seconds for large diameters)?
      3. If YES: Rapid flapping of the valve due to high velocity reverse flow is the likely root cause. Go to step 4.
      4. If NO: Other causes of water hammer are possible. Go to step 5.
4. Determining the cause of rapid slamming:
   1. Valve type:
      1. Is this a rotary valve in a vertical or high flow line? (Almost guarantees a slam).
      2. Is it a lift valve with a heavy disc?
      3. If YES: The valve is not suitable for the application.
   2. Absence/malfunction of damper:
      1. Is a damping device (hydraulic, pneumatic) installed?
      2. If so, is it properly set up or working (check oil level, air pressure, no leaks)?
      3. If the damper is missing or faulty: This is the main reason.
   3. System characteristics:
      1. Are there long pipes or high elevation differences after the valve? (Contributes to quick reversal).
      2. Are there no air-vacuum valves at high points in the pipeline?
   4. General conclusion: Root cause identified. Go to step 7 (Root Cause Analysis).
5. Diagnosis of system transients (if valve closing speed is not the only cause):
   1. Analysis of pump shutdown/on sequence:
      1. Does water hammer always occur when a specific pump is turned off?
      2. Is there a simultaneous shutdown of several pumps?
      3. Is there a rapid closing of another shut-off valve in the system causing a pressure pulse?
      4. If YES: The problem is related to the dynamics of the pumping station or the interaction of the fittings.
   2. Pipe elasticity check:
      1. Is the pipeline made of low Young's modulus materials (eg plastic) or has long unsupported sections?
      2. This can lead to resonant oscillations.
   3. General conclusion: Root cause identified. Go to step 7 (Root Cause Analysis).
6. Diagnosis of hidden mechanical defects of the valve (if other causes are excluded):
   1. Wear of internal parts:
      1. Dismantle the valve (after LOTO and decompression).
      2. Check the disc, stem, saddle for wear, corrosion, damage.
      3. Alarm threshold: The gap between the disk and the seat is more than 0.5 mm (for DN100-200) or visible burrs, deep erosion.
   2. Clogs:
      1. Check the inside of the valve cavity for foreign objects or deposits preventing smooth closing.
   3. Spring failure (if any):
      1. Assess spring stiffness and integrity. Does it meet the specification?
      2. If there are defects: This may prevent proper closing or cause slamming.
   4. General conclusion: Root cause identified. Go to step 7 (Root Cause Analysis).
7. Go to root cause analysis and remediation.

6. Matrix of malfunctions and causes

7. Root cause analysis for each malfunction

A. Rapid flapping of the check valve due to high rate of reverse flow

Explanation: This cause is the most common form of hydraulic shock in check valve systems. After the pump stops, the liquid flow slows down, and then, under the action of the liquid column or pressure from the receiving system, begins to move in the opposite direction. If the reverse speed reaches significant values ​​before the valve is fully closed, the valve disc suddenly "slams" against the seat. This creates a pressure shock wave that propagates through the pipeline. Impact energy is proportional to the mass of the valve disc and its closing speed.

Confirmation: Confirmed by high-speed pressure and flow rate monitoring. The record shows a short period of backflow (eg >0.5 m/s) immediately before a sharp, almost vertical pressure jump exceeding the operating pressure by 5-10 bar or more. The rise time of the pressure peak is usually milliseconds.

Consequences: If not eliminated, it will lead to: fatigue of the valve and pipeline material, wear of the valve seat and disc, destruction of the seals, failure of the valve stem, deformation or rupture of the pipeline, damage to the pump units (bearings, seals).

B. Wrong type of check valve for the application

Explanation: Choosing the wrong check valve type for a specific operating condition is a common root cause. For example, a standard check valve in a vertical pipe with upward flow or in a system with frequent pump stop/starts where flow reversal occurs quickly will almost always snap. Heavy lifter valve discs also have significant inertia, which slows them to close before backflow begins.

Confirmation: Comparison of installed valve type with valve manufacturer recommendations and industry standards (eg EN 14341) for similar flow conditions and system dynamics. Analysis of flow reversal rate versus estimated valve closing time.

Consequences: Repeated hydraulic shocks, increased valve wear, need for frequent replacement or repair, risk of accidents. This is a fundamental problem that cannot be solved by regulation alone.

C. Absence or failure of damping devices

Explanation: Damping devices (eg hydraulic or pneumatic shock absorbers, closing assist springs) are designed to slow the movement of the valve disc during closing. Their absence or malfunction allows the valve to slam uncontrollably. Improper tuning (such as too stiff a spring or not enough damping) can also make the problem worse.

Confirmation: Visual inspection for the presence of a damper. Checking the oil level in the hydraulic dampers, the air pressure in the pneumatic dampers, the integrity of the springs. Valve closing time testing with damper activated/deactivated (if applicable).

Consequences: Direct path to water hammer. Damage to the damper can also cause it to fail completely, leaving the valve unprotected.

D. System transients (e.g., quick pump shutdown)

Explanation: Hydraulic shock is not always solely a valve problem. Sometimes it is caused by rapid changes in the entire system, for example, the emergency shutdown of one or more pumps in a parallel system, which leads to a sudden loss of head and a rapid reversal of flow in the common manifold. Uncontrolled closing of other shut-off valves can also create pressure pulses.

Confirmation: Analysis of ACS event logs to identify correlation of water hammer with pump shutdown or other system events. Modeling pipeline transients can confirm the systemic nature of the problem.

Consequences: More extensive damage than a localized valve problem, as the shock wave can spread over large sections of the pipeline, affecting multiple components.

8. Step-by-step elimination procedures

A. Optimizing the closing speed of the non-return valve

1. Selecting the correct valve type:
   1. For systems with frequent flow reversals or high reversal rates: consider installing axial flow check valves or tilting disc check valves. These valves have less inertia of moving parts and less disc travel, allowing for faster closing before significant backflow occurs.
   2. Parameters: Select a valve with the lowest coefficient of flow resistance (Cv) required for your application to avoid excessive pressure loss. Comply with EN 16767 and ISO 10434.
2. Installation/adjustment of damping devices:
   1. Hydraulic dampers: If the valve has a built-in hydraulic damper (such as an oil cylinder), check the oil level and quality (according to the manufacturer's instructions). Adjust the throttle opening to increase the closing time to 0.5-2 seconds (for DN150-DN300 valves, the exact time depends on the system and pump characteristics).
   2. Air dampers: Check the air pressure in the air damper. It should meet the recommended 4-6 bars to ensure adequate damping.
   3. External dampers: Consider installing external hydraulic cylinders to control the closing speed of large diameter valves.
3. Spring-loaded check valves:
   1. For small diameters and systems with high pressure drop and rapid flow reversal, use spring-loaded check valves.
   2. Spring Selection: Make sure the spring has enough stiffness (10-20% design force of flow force) to accelerate closing, but not so stiff as to cause excessive pressure drop.

B. Installation of water hammer protection devices

1. Hydraulic accumulators / Hydraulic shock compensators:
   1. Install the hydraulic accumulator with a nitrogen cushion or diaphragm as close as possible to the check valve causing the problem.
   2. Settings: The initial pressure in the hydraulic accumulator should be 10-20% lower than the minimum working pressure of the system. The volume of the accumulator is calculated based on the volume of the reversing liquid and the permissible pressure drop.
2. Air-Vacuum Valves:
   1. Install at high points in the pipeline to prevent vacuum build-up after the pumps are shut off quickly.
   2. Size: The size of the valve should allow a quick intake/exhaust of sufficient air volume to avoid negative pressure peaks.
3. Time-controlled shut-off valves:
   1. Use hydraulic or electrically operated pump discharge valves that provide smooth closing within 5-15 seconds after the pump stops.

C. Optimizing the operation of the pumping station

1. Smooth start/stop of pumps:
   1. Introduction of frequency converters or soft starters for pumps.
   2. Settings: Adjust the pump acceleration/deceleration time to 10-30 seconds to gradually increase/decrease the flow rate.
2. Coordinated shutdown of pumps:
   1. In systems with parallel pumps, program sequential shutdown of units, not simultaneous.

D. Reinforcement of the pipeline system

1. Reinforcement of supports and anchors:
   1. Inspect and reinforce pipeline supports and anchors, especially near valves and diversions.
   2. Pitch of the supports: Check the correspondence of the step of the supports according to EN 13480 and the recommendations of the pipeline manufacturer.
2. Installing compensators:
   1. In some cases, installing rubber or metal compensators can help absorb some of the impact energy.

9. Preventive measures

10. Spare parts and components

Timely replacement of worn or damaged components is critical to prevent reoccurrence of water hammer.

To order quality spare parts and components, visit the UNITEC-D electronic catalog .

11. Links

• DSTU EN 13480: Industrial metal pipelines.
• ISO 10816: Mechanical vibration. Evaluation of machine vibration by measurements on non-rotating parts.
• EN 14341: Industrial pipeline fittings. Check valves made of steel, cast iron and copper alloys.
• DSTU OHSAS 18001 (or ISO 45001): Occupational health and safety management systems.
• Pump and valve manufacturers (OEM) operating and maintenance instructions.
• UNITEC-D Maintenance Guides: www.unitecd.com/maintenance-guides/.