1. Problem Description and Scope

Water hammer, or hydraulic hammer, is a transient overpressure phenomenon that occurs in hydraulic systems due to an abrupt change in fluid flow velocity. In check valves, this mainly manifests itself after rapid valve closure, when reverse flow is established and is suddenly stopped. This guide covers diagnosing and resolving water hammer problems associated with check valves in industrial environments, with a focus on:

• Excessive noise and vibration in piping and adjacent components.
• Structural damage to piping, supports and connections.
• Premature wear and failure of the check valve itself, pumps and other system equipment.
• Sudden and dangerous pressure variations that can affect process integrity and operational safety.

This guide is applicable to pumping systems, water distribution networks, industrial process lines, and other installations that employ check valves to prevent backflow. The severity of water hammer can be classified as:

• Critical: Imminent risk of pipeline rupture, catastrophic equipment failure, danger to personnel. Requires immediate action.
• Majority: Accelerated wear, recurring component failures, unscheduled production stoppage. Needs urgent planned intervention.
• Minority: Audible noise, slight vibration, no immediate damage. Indicative of a latent problem that must be corrected to avoid escalation.

2. Safety Precautions

CRITICAL SAFETY WARNING: Before any inspection, diagnosis or intervention on pressurized systems, it is mandatory to strictly follow the Lockout and Tagout (LOTO – Lockout/Tagout) procedures to ensure that all energy sources (electrical, hydraulic, pneumatic, mechanical) are isolated and zeroed. The energy stored in pressurized hydraulic systems can be lethal. Verify complete system depressurization before opening flanges or removing components.

Essential PPE: Always wear safety gloves, protective glasses (NBR ISO 166:2009), hearing protection (ABNT NBR 16071:2012), safety helmet (ABNT NBR 8221:2003) and safety shoes (ABNT NBR ISO 20345:2015). For hot or corrosive fluids, add face protection and appropriate clothing. Observe the guidelines of NR-10 for working with electricity and NR-12 for operating machines and equipment.

3. Required Diagnostic Tools

Below is a list of essential tools for an accurate diagnosis of water hammer, with specifications and purposes:

4. Initial Assessment Checklist

Before beginning any active diagnosis, perform a thorough initial assessment. Record all information to contextualize the problem.

5. Systematic Diagnostic Flowchart

This flowchart guides the technician through a logical path to identify the root cause of water hammer in check valves.

1. Does water hammer occur immediately after the pump stops or the flow stops?
   • IF YES:
   1. Is the noise/vibration sharp, like a "hammer"?
      • IF YES: Probable rapid and violent closing (slam) of the check valve.
      1. Check the type of check valve installed.
         • Is it a tilting disc valve in a fast reverse flow system?
           • IF YES: High probability of inadequacy. Rocker valves are slow and susceptible to slamming in fast reverse flow.
           • IF NOT: Continue the diagnosis.
         • Is the valve a "no-slam" type (piston or double port with spring) and the problem persists?
           • IF YES: The spring may be inadequate or broken, or the internal shock absorber has failed.
           • IF NOT: The valve may not be functioning as expected (incorrect spring, sticking).
      2. Install pressure transducers and data loggers. Record pressure spikes during shutdown.
         • Do pressure spikes exceed 1.5 times normal working pressure? (Alarm value: Peak pressure > 1.5 * Operating pressure)
           • IF YES: Confirms significant water hammer.
           • IF NOT: The noise may have another origin (cavitation, pump vibration). Reevaluate.
      3. Use the ultrasonic flow meter. Is reverse flow detected before the valve closes?
         • IF YES: This indicates that the valve is closing after flow reversal, generating the stroke.
         • IF NOT: The valve may be closing before inversion, but very quickly.
   2. IF NO (Constant or intermittent noise/vibration, but not sharp): The problem could be resonance, cavitation in the pump, or component vibration. Reevaluate the main symptom.
   • IF NOT: Water hammer is not directly related to the pump stopping. Investigate other causes of transients such as rapid closing/opening of other valves, pump starting, or filling/emptying of lines. This guide focuses on pump stop/reverse flow.
2. Does the check valve have any damping mechanism (external or internal)?
   • IF YES:
   1. Check the shock absorber operation.
      • Is it a hydraulic shock absorber?
        • Check the oil level, leaks, closing needle adjustments.
        • Is the damper set for the appropriate closing time (usually 2 to 5 seconds)?
          • IF NOT: Adjust the closing time.
          • IF YES: The shock absorber may be dirty, clogged or incorrectly sized.
      • Is it a valve with an internal spring?
        • Is the spring corroded, weak or broken? (Usually requires disassembly to check)
        • Is the spring strength adequate for the operating pressure and desired closing time? (Very weak springs are ineffective).
   • IF NOT: The absence of a damping mechanism could be the root cause. Consider installing dampers or replacing them with soft-closing ("no-slam") check valves.
3. Analysis of the Piping System and Pump:
   • Does the system have pressure accumulators or expansion vessels?
     • IF YES: Check the pre-charge (inert gas) of the accumulator. Incorrect preload (~70% of operating pressure) may disable its damping function.
     • IF NOT: The lack of these devices can worsen water hammer.
   • Does the pump have enough inertia to gradually slow the flow?
     • IF NO: Low inertia pumps in long, high-speed systems are more prone to water hammer.
   • Is the length of piping between the pump and check valve long?
     • IF YES: Long piping increases fluid volume and kinetic energy, exacerbating water hammer.

6. Failure-Cause Matrix

This matrix correlates the observed symptoms with the probable causes, diagnostic tests and expected results to confirm the failure. The causes are classified by probability (High, Medium, Low).

7. Root Cause Analysis for Each Failure

Understanding the reason for each failure is crucial for prevention.

7.1. Improper Check Valve Selection

• Explanation: Swing check valves are common, but their closing time is inherently slow. In systems with high flow velocity or where reverse flow establishes quickly (e.g. high discharge pumps, vertical pipelines), the disc cannot close completely before the reverse flow accumulates significant kinetic energy.
• How to Confirm: The ultrasonic flow meter detects significant reverse flow before disc closure. The pressure transducer registers a single, sharp pressure peak.
• Damage if Unresolved: Repetitive impact causes damage to the seat, disc, pivot pin, which can lead to valve failure, broken pipes and damage to the pump.

7.2. Incorrect Valve Sizing

• Explanation: A check valve oversized for normal system flow often operates in a "partially open" condition. This means that the disc or piston never reaches the fully open position, or it floats, resulting in turbulence and wear. When stopping the pump, the closing is inconsistent.
• How to Confirm: Valve inspection reveals irregular disc/seat wear. Comparison of the operational flow with the minimum flow for full opening of the check valve (see manufacturer's Cv curve).
• Damage if Unaddressed: Premature wear, internal leakage, and improper closure that can exacerbate water hammer.

7.3. Excessively Fast Reverse Flow

• Explanation: In systems with high discharge pumps, long piping and significant unevenness, the fluid column can reverse direction very quickly after the pump stops. If the check valve is not designed to close faster than the rate of fluid deceleration, "slam" is inevitable.
• How to Confirm: Transient analysis with data logger and flow meter. The flow reversal time is very short (milliseconds to a few seconds).
• Damage if Unresolved: The most common and violent type of water hammer, causing severe damage to the system structure and equipment.

7.4. Absence or Failure of Dampeners

• Explanation: Check valves designed for soft closing ("no-slam" type) generally incorporate springs or hydraulic/pneumatic shock absorbers. The absence of these devices, their failure (broken/weak spring, leak in the shock absorber) or incorrect adjustment prevents control of the closing speed.
• How to Confirm: Visual inspection of the valve. If it is a model with a spring, you need to disassemble it to check the integrity of the spring. For hydraulic shock absorbers, check fluid level and adjustments. Water hammer is common in valves that should be soft-closing.
• Damage if Unaddressed: The valve operates as a simple check valve, exposing the system to the same risks as improper selection.

7.5. Incorrect System Configuration or Operation

• Explanation: An abrupt stop of the pump without a gradual shutdown procedure (deceleration ramp), or sudden power failure, can create ideal conditions for water hammer. Systems without expansion vessels or pressure accumulators may not be able to absorb pressure waves.
• How to Confirm: Analysis of operational procedures and system design. Checking nitrogen pre-charge in accumulators.
• Damage if Unresolved: Continued vulnerability of the system to pressure transients, even with adequate check valves.

8. Step-by-Step Resolution Procedures

Corrective actions must be implemented after identifying the root cause.

8.1. For Improper Valve Selection or Incorrect Sizing

1. SECURITY: Run full LOTO on the system. Depressurize the line.
2. Valve Replacement:
   1. Remove the existing check valve.
   2. Install a quick-closing check valve (double-port or spring-loaded piston type) or a no-slam valve (soft closing assisted by a hydraulic shock absorber or spring). Make sure the new valve is correctly sized for the minimum and maximum operating flow. Consult the manufacturer's performance curves (e.g. CV) to ensure optimal selection.
   3. Installation: Follow the manufacturer's recommendations for orientation (horizontal/vertical) and flange tightening torques (ABNT NBR 16327:2014 for flanges).
3. Post-Repair Check:
   1. Commission the system gradually, monitoring pressures and flows.
   2. Repeat the pump start/stop cycle and record pressure peaks with the transducer. The peak pressure must be less than 1.25 times the normal operating pressure (acceptable value).
   3. Monitor noise and vibrations. Vibration levels in the piping must be below 10 mm/s RMS.

8.2. For Excessively Fast Reverse Flow or Absence of Damping

1. SECURITY: Run full LOTO. Depressurize the line.
2. Installation/Adjustment of Shock Absorbers:
   1. External Shock Absorbers: Install an adjustable hydraulic shock absorber on the existing check valve, if permitted. Adjust the closing needle for a valve closing time between 2 to 5 seconds, depending on the system dynamics.
   2. Integrated Hydraulic Dampers: If the valve is a piston type with damping, check and adjust the damping hole or hydraulic fluid level.
   3. Springs: For valves with springs, replace the spring with one with an adequate compression rate, ensuring quick but not violent closing.
3. Post-Repair Check:
   1. Monitor stop and start cycles.
   2. Record pressure peaks. The objective is to reduce the peak pressure to less than 1.25 times the operating pressure.
   3. Confirm smooth closing of the valve without audible noise or excessive vibration.

8.3. For Incorrect System Configuration or Operation

1. SAFETY: Only change control parameters after LOTO and with knowledge of the impact.
2. Implementation of Soft Start/Stop Controls:
   1. Install or configure frequency inverters (VFDs) for pumps, allowing for controlled acceleration and deceleration ramps. A deceleration ramp of 5 to 10 seconds can be effective in reducing the blow.
   2. Install or check the functionality of pressure relief valves or expansion vessels.
3. Post-Repair Check:
1. Monitor VFD performance and system response during pump shutdown.
2. Use the data logger to record the pressure and flow curve during shutdown, seeking a smooth profile.

9. Preventive Measures

Prevention is the most effective strategy to avoid water hammer and its associated costs.

10. Spare Parts and Components

The availability of spare parts is essential for quick and effective intervention. Please refer to the UNITEC-D electronic catalog for detailed specifications.

For consultation and purchase of parts, visit our electronic catalog: www.unitecd.com/e-catalog/

11. References

• ABNT NBR 15827:2010: Industrial valves – Check valves – Design and manufacturing requirements.
• ABNT NBR 16327:2014: Flanges and flange joints – Nominal pressure.
• ISO 10816-3:2009: Mechanical vibration – Measurement and evaluation of machine vibration – Part 3: Industrial machines with nominal power greater than 15 kW and nominal speeds between 120 r/min and 15,000 r/min when measured in bearings.
• NR-10: Safety in electrical installations and services. (Ministry of Labor and Employment, Brazil).
• NR-12: Safety at work on machines and equipment. (Ministry of Labor and Employment, Brazil).
• Valve Engineering Manual: Guidelines for the selection and application of industrial valves.
• Hydraulic Transient Analysis: Fundamentals and applications in pumping systems.

1. Problem Description and Scope

Water hammer in check valves is a critical hydraulic phenomenon characterized by rapid and intense pressure fluctuations in a piping system resulting from the abrupt closing of a check valve. This event typically occurs after the sudden stop of a pump or rapid reversal of flow, when the column of moving fluid reverses its direction and "slams" against the valve closing mechanism, generating shock waves. Symptoms include "knocking" or "hammering" noises, excessive vibration in the piping, joint leaks, instrument failure and, in extreme cases, piping rupture or irreparable damage to the pump and valve itself.

This guide covers the diagnosis and resolution of water hammer in fluid systems, being applicable to a wide range of industrial equipment, such as water and effluent pumping stations, refrigeration and HVAC systems, chemical processes, oil and gas industries, and fluid transport systems in general. Classifying the severity of this problem is CRITICAL as it can lead to:

• Unscheduled production stoppages.
• Safety risks to personnel due to structural failure of equipment.
• High repair and replacement costs for damaged components.
• Product loss and environmental impacts.

The goal is to provide a systematic methodology for maintenance technicians and field engineers to identify the root cause of water hammer and implement effective solutions to mitigate its effects.

2. Safety Precautions

IMMINENT DANGER: Systems under pressure and with moving fluids pose serious risks. Safety is essential at all stages of diagnosis and intervention.

• LOCKOUT/TAGOUT (LOTO): Before any physical intervention on the system, ensure that all energy sources (electric, hydraulic, pneumatic) are isolated and blocked in accordance with regulatory standard NR-10 and your company's internal procedures.
• RESIDUAL PRESSURE RELIEF: Check and completely relieve system pressure through bleed or drain valves before loosening flanges, removing instruments, or disassembling any components. The fluid may be pressurized even when the pump is stopped.
• ADEQUATE PPE: Always use the correct Personal Protective Equipment (PPE) for the task, including, but not limited to: safety glasses or face shield, chemical/thermal resistant gloves, hearing protection, hard hat and safety shoes.
• EXTREME TEMPERATURES: Many process fluids operate at high or low temperatures. Be careful with hot or cold surfaces and use thermal gloves if necessary.
• DANGEROUS FLUIDS: In case of leaks, be aware of the nature of the fluid (corrosive, flammable, toxic) and take appropriate precautions for containment and protection. Consult the product's Safety Data Sheet (SDS).
• STORED ENERGY: Be careful with springs in valves or pressure accumulators that can release energy unexpectedly.

3. Required Diagnostic Tools

Diagnostic accuracy depends on the use of appropriate equipment. Below is a list of essential tools:

4. Initial Assessment Checklist

Before beginning any complex diagnostic procedure, a detailed initial assessment is essential to contextualize the problem and direct testing.

5. Systematic Diagnosis Flowchart

This flowchart guides the technician through a logical path to isolating the root cause of water hammer.

1. Main Symptom: "Knocking" noise or excessive vibration in the piping immediately after closing the check valve.
   1. Step 1: Quantify Pressure Spikes.
      • Install dynamic pressure transducers (upstream and downstream of the check valve).
      • Record data using a high-speed datalogger during the event of pump shutdown or flow reversal.
      • Result Analysis:
        • Result A: Pressure Peak > 1.5x Nominal Operating Pressure (P_nominal) or Depression Peak < P_atmospheric: Indicates a severe water hammer. Proceed to Step 2: Analyze Valve Closure.
        • Result B: Peak Pressure < 1.5x P_nominal (but noise present): Water hammer may not be the primary cause or is of lesser intensity. Proceed to Step 3: Assess Structural Integrity and Resonance.
        • Result C: No Significant Pressure Spikes: The noise/vibration is not primarily caused by water hammer. Investigate other sources (e.g. pump cavitation, misalignment, mechanical play).
   2. Step 2: Analyze Check Valve Closure.
      • If possible and safe (after LOTO and pressure relief), perform an external visual inspection or use an industrial stethoscope to listen for closure. In transparent systems, observe the movement of the disk.
      • If the valve has an actuator, check its response time.
      • Result Analysis:
        • Result A: Slow, Incomplete or Oscillating Valve Closing:
          • Probable Cause 1: Contamination or Internal Obstruction.
          • Probable Cause 2: Wear of the Internal Mechanism (pin, spring, seat).
          • Action: Go to the "Root Cause Analysis" section for "Valve Wear or Mechanical Failure" and "Internal Contamination or Obstruction".
        • Result B: Rapid and Abrupt Closing ("Valve Slam"):
          • Check System Conditions:
            • 2.1: System with Long Fluid Column and/or High Flow Velocity:
              • Probable Cause 3: High Fluid Column Inertia and Rapid Reversal.
              • Action: Go to the "Root Cause Analysis" section for "Fluid Column Inertia and Rapid Reversal".
            • 2.2: Traditional Flap or Disc Check Valve in Applications with Rapid Flow Reversal:
              • Probable Cause 4: Inadequate Check Valve Selection for the Application.
              • Action: Go to the "Root Cause Analysis" section for "Improper Check Valve Selection".
            • 2.3: Presence of Air or Gas in the System (Bubbles, Bubbling Noise):
              • Probable Cause 5: Compressibility of the Fluid/Gas in the System.
              • Action: Go to the "Root Cause Analysis" section for "Air or Gas in System".
   3. Step 3: Assess Structural Integrity and Resonance.
      • Perform vibration analysis at multiple points of the piping, supports and pump casing.
      • Visually inspect all piping supports, ties and anchors to check for looseness, corrosion or damage.
      • Result Analysis:
        • Result A: High Vibration Levels in Piping and/or Pump (e.g. > 7.1 mm/s RMS) with Periodic Patterns:
          • Probable Cause 6: Excessive Pump Pulsation or System Resonance.
          • Action: Go to the "Root Cause Analysis" section for "Pump Pulsation or System Resonance".
        • Result B: Loose, Broken or Missing Brackets:
          • Probable Cause 7: Structural Failure and Vibration Transmission/Amplification.
          • Action: Go to the "Root Cause Analysis" section for "Structural Failure and Vibration Transmission".

6. Matrix of Failures and Probable Causes

This table correlates symptoms with probable causes, ordered by likelihood, and suggests diagnostic tests with expected results for confirmation.

7. Detailed Root Cause Analysis

7.1. Fluid Column Inertia and Rapid Reversal

Explanation: When a pump is turned off, especially in long discharge lines or in systems with high elevations, the fluid column has considerable inertia. This inertia causes the fluid to continue moving for a brief period, creating a zone of low pressure (depression) downstream of the pump. Eventually, the fluid slows, stops, and reverses direction. If the check valve, which is supposed to prevent this backflow, does not close completely before the reverse column velocity becomes significant, the valve disc or flapper is "slammed" violently against the seat. This impact generates a high-pressure shock wave – water hammer – which quickly propagates through the pipe.

How to Confirm: The use of dynamic pressure transducers connected to a datalogger is the most effective way. The recorded data will show a sudden pressure drop (depression) shortly after the pump is turned off, followed by a sudden, significantly high pressure spike (usually 2 to 5 times the rated operating pressure, or even higher) when the valve closes. The flow reversal speed can be confirmed by ultrasonic flow meters during the event.

Potential Damage: If not resolved, it causes metal fatigue in the piping, ruptures in welds and flanges, misalignment and damage to pump bearings and seals, premature failure of the check valve (broken disc/portlet, deformed seat) and damage to instruments and supports.

7.2. Improper Check Valve Selection

Explanation: Not all check valves are suitable for all applications. Conventional check valves, such as swing check valves or springless lift check valves, rely on flow to keep them open and gravity or backflow to close them. In systems with very rapid flow reversal or where the fluid column decelerates rapidly, these valves may not close in time, allowing the fluid to reverse and cause the disc to "slam" against the seat. An oversized valve may also have difficulty closing due to low fluid velocity.

How to Confirm: Compare the dynamic characteristics of the system (flow deceleration speed, inversion time) with the specifications of the installed valve. Consult manufacturers' catalogs and manuals. Evaluate the DN (Nominal Diameter) of the valve in relation to the actual system flow. A correctly selected valve must close before the backflow velocity reaches 0.3 m/s.

Potential Damage: Recurrent water hammer, constant noise, vibration, accelerated wear of the valve and adjacent components.

7.3. Valve Wear or Mechanical Failure

Explanation: Internal valve components, such as the pivot pin, stem, disc/port, spring (if present), or seat, may wear due to corrosion, erosion, cavitation, or material fatigue. A weakened or broken spring prevents quick closing. Debris accumulated in the seat can prevent complete closure, causing internal leakage and allowing flow to reverse before complete closure. Any of these factors compromise the valve's ability to close efficiently and on time.

How to Confirm: After blocking and relieving pressure, the valve must be dismantled and visually inspected. Check the condition of the seat surface and the disc/door, the integrity of the spring (if present), the clearance of the pins and the alignment of the stem. Bench tests can be carried out to check tightness and closing force.

Potential Damage: Internal and external leaks, loss of system efficiency, water hammer due to late or incomplete closing, need for premature valve replacement.

7.4. Air or Gas in the System

Explanation: The presence of air or gas pockets in a liquid system is extremely harmful. Unlike liquids, gases are compressible. During a water hammer event, these bubbles act as a "spring", absorbing the energy of the pressure wave and releasing it in a sudden and uncontrolled manner. This can amplify the intensity of water hammer, generate localized cavitation and cause irregular and noisy closing of the valve.

How to Confirm: Symptoms include bubbling noise in the system, unstable pressure readings, erratic closing of the check valve. Bleeding from high points in the piping or using level sensors can confirm the presence of air.

Potential Damage: Intensified water hammer, cavitation, oxygen corrosion, inaccurate process measurements, failure of seals and gaskets.

7.5. Pump Pulsation or System Resonance

Explanation: Positive displacement pumps (piston, diaphragm) generate pulsations naturally. Even centrifugal pumps can generate pulsations if operating too far from their Best Efficiency Point (BEP) or due to unbalance. If the frequency of these pulsations coincides with the natural frequency of vibration of the piping or check valve components, resonance occurs. This amplifies vibrations, overloads the supports, and can induce improper valve closure, indirectly contributing to water hammer or masking other problems.

How to Confirm: A detailed spectral vibration analysis using accelerometers will reveal frequency peaks. Correlating these frequencies with pump speed, number of impeller vanes, or other sources of pulsation will confirm the cause. Modal analysis simulations can be used to identify pipeline natural frequencies.

Potential Damage: Piping fatigue, loosening of connections, instrument failure, support rupture, excessive noise, damage to pump and valve mechanical seals.

8. Step-by-Step Resolution Procedures

8.1. For Fluid Column Inertia and Rapid Reversal

Objective: To reduce the inertia of the fluid column or allow the valve to close before the reversal velocity becomes destructive.

1. Assess the Hydraulic System: Perform a hydraulic transient analysis to understand pressure and flow dynamics during pump shutdown. Simulation software can be used.
2. Install Quick-Close Check Valves:
   • Replace traditional flap or disc check valves with more efficient models such as:
   • Nozzle Check Valves: They have a light disc and a very short stroke, allowing extremely fast closing.
   • Damped Piston Check Valves: They use an oil or air-cushioned piston to control the closing speed, avoiding "slam". Adjust damping to optimize closing time.
   • Axial Disc Check Valves: Quick closing and low pressure loss.
3. Install Pulsation Dampers / Expansion Vessels: Size and install hydropneumatic accumulators or expansion vessels in the pump discharge line. These devices absorb excess energy from pressure peaks.
4. Variable Speed ​​Controllers (VFD): If the pump is driven by a VFD, adjust the deceleration ramps to extend the stopping time, allowing the check valve to close more smoothly. A 10-15 second deceleration ramp is a good starting point, but should be optimized.
5. Verification: After implementing the measures, repeat the monitoring with pressure transducers. Peak pressure must be < 1.25x P_nominal and blow noise must be eliminated or significantly reduced.

8.2. For Improper Check Valve Selection

Objective: Ensure that the check valve is compatible with the dynamic characteristics of the system.

1. Engineering Review: Perform a complete review of valve specifications against system design parameters: maximum/minimum flow, pressure, fluid type, temperature, flow reversal time, and allowable head loss. See ABNT NBR 15509 standards.
2. Valve Resizing: If the valve is oversized, it may not have enough flow to operate the shutoff mechanism correctly. Consider replacing it with a valve of nominal diameter (DN) appropriate for the operating flow rate.
3. Replacement by Suitable Type: Based on the analysis (Section 7.2), select and install a check valve with quick closing characteristics such as those mentioned in 8.1.2.
4. Verification: Monitor the system during operation. Check that the valve closes smoothly and that there is no abnormal noise or vibration.

8.3. For Valve Wear or Mechanical Failure

Objective: Restore full functionality of the check valve.

1. CAUTION: Lockout/Tagout (LOTO) and Pressure Relief are ABSOLUTELY MANDATORY!
2. Disassembly and Inspection: Carefully disassemble the valve. Inspect the disc/door, seat, pivot pin/rod, and spring (if present). Search for:
   • Signs of corrosion, erosion, cavitation.
   • Excessive wear on sealing surfaces (seat and disc).
   • Deformed, weak or broken spring.
   • Pivot pin with excessive play or worn.
   • Accumulation of debris or scale.
3. Replacement of Damaged Components: Replace any worn or damaged parts using original manufacturer repair kits or UNITEC replacement parts of equivalent quality.
4. Cleaning: Remove all debris, scale and corrosion from the internal surfaces of the valve.
5. Reassembly: Carefully reassemble the valve, applying tightening torques to the flanges and connections according to the manufacturer's specifications. Make sure the disc/door moves freely and sits correctly in the seat.
6. Functionality Test: Before pressurizing, manually check the movement of the mechanism. After pressurization (gradual), perform a tightness test to detect leaks and observe the closure in operation.

8.4. For Air or Gas in the System

Objective: Eliminate the presence of air or gas pockets to restore the fluid's incompressibility.

1. Identify Air Entry Points: Inspect the pump suction line, gaskets, mechanical seals, flanges and drain points for leaks that may be introducing air into the system. Perform soap tightness or pressure leak tests (if the system can be isolated).
2. Purge the System: Use the purge/ventilation valves located at the high points of the piping to release accumulated air or gas. Do this gradually and safely, using appropriate PPE.
3. Install Air Elimination Valves: In systems prone to air accumulation, consider installing automatic air elimination valves at strategic points.
4. Verification: Observe the system in operation. The bubbling noise should cease, pressure readings should stabilize, and the check valve closing should be smooth.

8.5. For Pump Pulsation or System Resonance

Objective: Mitigate the pulsations generated by the pump and avoid resonance amplification.

1. Pump Operation Optimization: Verify that the pump is operating as close to its Best Efficiency Point (BEP) as possible. Operation far from the BEP may generate pulsations. Adjust the flow rate or use a VFD to operate the pump in a more efficient range.
2. Dynamic Balancing: If the cause is unbalance, perform dynamic balancing of the pump impeller.
3. Install Pulsation Dampers: In positive displacement pumps, installing pulsation dampers at the discharge is essential to smooth the flow and reduce pressure waves.
4. Review of Supports and Anchors: Reinforce or add supports to the piping to increase rigidity and change natural vibration frequencies, preventing resonance.
5. Verification: Perform a new vibration analysis. RMS vibration levels must be within acceptable limits (e.g. < 4.5 mm/s for normal operation). Peak frequencies must be reduced or eliminated.

9. Preventive Measures

Prevention is always the most economical and safe approach. The following measures can prevent the recurrence of water hammer:

10. Spare Parts and Components

Maintaining an adequate inventory of replacement parts is crucial for a quick and effective response to water hammer problems. UNITEC-D offers a wide range of high quality components.

For more information about these components and other products, visit our e-catalog: www.unitecd.com/e-catalog/

11. References

• ABNT NBR 10839: Centrifugal Pumps – Installation.
• ABNT NBR 15509: Industrial Valves – Selection and Sizing.
• ABNT NBR ISO 10816-3: Assessment of machine vibration by measurements on non-rotating parts – Part 3: Industrial machines with nominal power greater than 15 kW and nominal speeds between 120 r/min and 15,000 r/min when measured in situ.
• Pump and valve Original Manufacturer (OEM) manuals.
• Other UNITEC-D Maintenance Guides related to hydraulics and pumps.