Helpful Hints

Jul 31, 2026      Nick Pavlovic Inside Technical Sales - Yamada America, Inc.

Preventing Water Hammer

Nick Pavlovic - Inside Technical Sales - Yamada America, Inc.

Water hammer is one of the more common—and costly—issues encountered in industrial pumping systems. In simple terms, water hammer is a sudden pressure surge within a piping system caused by a rapid change in fluid velocity.

The most common causes of water hammer include rapid valve closures, sudden pump starts or stops, power failures, and improperly designed piping systems. Since energy cannot be created or destroyed, the kinetic energy of the moving fluid must go somewhere when flow is stopped abruptly. Rather than disappearing, that energy is converted into a high-pressure wave by slightly compressing the liquid and elastically expanding the pipe walls. This pressure wave then travels back and forth through the piping system, reflecting off valves, elbows, tanks, and other components until its energy is gradually dissipated.

These brief pressure waves can generate far greater forces than the system's normal operating pressure, leading to damaged piping, leaking seals, broken valves, instrument failure, excessive vibration, and premature pump wear. Understanding how water hammer occurs is the first step in designing pumping systems that operate safely, reliably, and efficiently.

The next step is understanding how to prevent water hammer from occurring or, when it cannot be avoided, how to reduce and absorb the resulting pressure surge. One of the simplest solutions for water hammer caused by valve closure is to use a slow-closing valve. By gradually reducing the flow velocity instead of stopping it abruptly, the system experiences a smaller change in momentum, which reduces the magnitude of the pressure wave generated. It’s like hitting the brakes in a car to gradually come to a stop, versus slamming into a brick wall to stop immediately.

There are instances where pulsation and pressure spikes can occur even when valves are not abruptly closed. One example is the use of Air Operated Double Diaphragm (AODD) pump technology. AODD pumps operate by connecting two diaphragms through a center shaft, causing them to reciprocate back and forth in alternating cycles. As one diaphragm draws liquid into the pump, the opposite diaphragm simultaneously discharges liquid, and the process reverses on the next stroke.

Because flow in an AODD pump is generated through repeated acceleration and deceleration of the fluid column, each diaphragm stroke creates changes in fluid momentum. These changes in velocity require additional pressure energy to overcome the inertia of the fluid mass. This additional pressure requirement is known as acceleration head and appears as pressure fluctuations throughout the piping system.

While acceleration head is not the same phenomenon as traditional valve-induced water hammer, both are caused by changes in fluid velocity. Water hammer occurs when a rapid, near-instantaneous change in velocity generates a pressure wave through the piping system. Acceleration head occurs from the repeated acceleration and deceleration associated with normal reciprocating pump operation. These pressure fluctuations become more significant in systems with long piping runs, high operating pressures, large fluid volumes, or restrictive flow paths.

The acceleration head in the discharge line can be estimated using:

 

Where:

• = Acceleration head (ft of liquid)
• = Length of discharge line (ft)
• = Velocity in discharge line (ft/s)
• = Pump speed (cycles per minute)
• = Pump type constant
• 0.200 for duplex single-acting diaphragm pumps
• 0.115 for duplex double-acting pumps
• 0.066 for triplex single or double-acting pumps
• 0.040 for quintuplex single or double-acting pumps
• 0.028 for septuplex single or double-acting pumps
• 0.022 for nonuplex single or double-acting pumps
• = Fluid compressibility factor representing the fraction of theoretical acceleration head required to prevent noticeable disturbances
• 2.5 for hot oil
• 2.0 for most hydrocarbons
• 1.5 for amines and glycol
• 1.4 for deaerated water
• 1.0 for urea and liquids containing small amounts of entrained gas
• = Gravitational constant (32.174 ft/s²)

The equation demonstrates why piping length has such a significant impact on pulsation. As the discharge piping length increases, the amount of fluid mass being accelerated also increases. A larger fluid column requires more energy to change velocity, resulting in higher acceleration head and greater pressure fluctuations throughout the system.

During each diaphragm stroke, the fluid accelerates as the pump begins its discharge cycle and then decelerates as the stroke ends and flow reverses. This repeated change in momentum creates cyclic pressure fluctuations throughout the piping system. Unlike a sudden valve closure event, these pressure variations are typically not immediately catastrophic. However, continuous pulsation over time can contribute to mechanical fatigue and premature component wear, including loosening of bolts, stressing of fittings, degradation of seals, and increased vibration throughout the system.

One effective method to reduce these pressure fluctuations is the use of a pulsation dampener. A pulsation dampener provides a compressible air or gas chamber that absorbs energy from the fluid during high-pressure portions of the pump cycle and releases energy during low-pressure portions. This reduces the amplitude of pressure fluctuations, smooths the overall flow profile, and decreases stress transferred to downstream piping and equipment.

Preventing excessive pressure fluctuations requires considering the entire system, including pump type, piping layout, operating conditions, and flow control methods. Simple solutions such as slow-closing valves can reduce sudden velocity changes, while properly sized pulsation dampeners can absorb and smooth the cyclic pressure variations created by reciprocating pumps.

By accounting for acceleration head and minimizing unnecessary piping restrictions, engineers can reduce mechanical stress, improve pump reliability, and extend the service life of piping components. Ultimately, effective water hammer prevention is not about eliminating pressure changes entirely—it is about controlling how quickly those changes occur and managing the energy created when fluid momentum changes.

Need Help Evaluating Your System?

Need help evaluating pulsation, piping layout, or dampener selection? Contact your local Yamada representative for application assistance.

FIND MY REP

---