Water hammer is a recurring reliability problem in pumped liquid systems. It shows up in pipelines, pump stations, and process services where flow rates are high and operating margins are tight. Check valves are often involved, sometimes as protection and sometimes as the trigger. Their behavior during transient events determines how much stress the system sees when flow conditions change suddenly.
What is Water Hammer?
Water hammer happens when moving water is forced to slow down or stop too fast. The change in velocity creates a pressure spike. That spike travels through the pipe until it loses energy or hits a boundary.
Common triggers are pump trips, fast valve closures, and sudden changes in flow demand. High velocity makes the problem worse. Longer and stiffer piping gives the pressure wave more distance to build and reflect.
When the pressure wave hits closed valves, elbows, dead ends, or equipment, it reflects back into the system. Each reflection adds stress, and over time, this leads to noise, pipe movement, leaking joints, damaged supports and shorter valve and pump life.
How Check Valves Work
Basic function
Check valves are one-way devices that allow fluid to flow in a desired direction and automatically close to prevent reverse flow. They rely on differential pressure across the valve: forward flow opens the internal element (disc, plate, ball, or piston), while a drop or reversal in flow causes the element to move back to its seat and seal.
Main internal components
Depending on the design, the closure element may be hinged, guided, or spring-loaded, which determines how quickly and smoothly the valve responds to changing flow.
Opening behavior
When upstream pressure exceeds downstream pressure by a certain margin (the cracking pressure), the closure element is pushed off the seat and the valve opens. As flow increases, the element moves toward a more fully open position, reducing pressure drop across the valve and stabilizing flow through the line.
Closing behavior and dynamics
Compared to standard swing and tilting-disc designs, nozzle check valves—such as the axial-flow styles offered by ValvTechnologies—are engineered with a much shorter stroke and optimized spring-assisted closure. Because the disc travels only a small distance and begins closing as soon as velocity declines, nozzle check valves dramatically limit reverse flow buildup. This early, damped closure is one of the most effective ways to minimize the momentum change that causes water hammer.
As flow decelerates or reverses, the driving force holding the element open is reduced, and gravity, springs, or reverse flow move the element back toward the seat.
The speed and distance of this closing motion are critical for water hammer control, because excessive travel or delayed closure can allow more reverse velocity to build before the valve seats.
Relevance to water hammer
Among available non-slam technologies, nozzle check valves stand out because their axial-flow design naturally centers the disc, eliminates turbulence around the guide mechanism, and ensures extremely fast closure with minimal impact velocity. ValvTechnologies’ nozzle checks use carefully matched springs and trim geometry to prevent both slamming and flutter, even in systems with rapid transients.
In transients such as pump trips or rapid valve closures, check valves act as automatic safeguards against reverse flow. Designs with shorter stroke and controlled non-slam closure reduce pressure spikes, while slow or poorly damped designs can intensify water hammer in high velocity systems.
Pump Start and Pump Stop Transients
A nozzle check valve’s ultra‑short stroke and spring‑loaded axial movement allow it to close before damaging reverse velocity develops—something swing checks cannot achieve due to their long arc and inertia. In pump‑trip scenarios, this early closure is one of the most reliable ways to prevent high-intensity slam.
Water hammer behavior differs depending on when the transient occurs. Events during pump shutdown and pump startup create different flow conditions, and check valve behavior plays a different role in each case.
During pump shutdown, flow deceleration is driven by loss of energy input. If a pump trips while operating near maximum flow, the liquid column continues moving forward until system pressure decays. As flow reverses, the check valve closes. If closure occurs after substantial reverse velocity has developed, the disc seats abruptly and the momentum change produces a sharp pressure spike. Spring-assisted and short-stroke designs can reduce this effect by closing earlier in the deceleration cycle, but only if spring force and friction are matched to actual flow conditions.
During pump startup, multiple check valves in series can introduce a different risk. If downstream check valves hold a column of liquid while upstream pressure drops, a partial vacuum can form between valves. When the pump starts, the liquid column accelerates rapidly to refill that space. The resulting momentum can cause a severe impact when the upper check valve opens or reseats. In these cases additional check valves do not add protection and can increase transient severity.
For many systems, fewer check valves with predictable dynamic behavior perform better than multiple valves installed for redundancy alone. Placement, closing speed, and interaction with system pressure profiles influence transient response more than valve count.
Check Valve Types Used for Water Hammer Control
- Nozzle (Axial‑Flow) Check Valves: Nozzle check valves use an axial-flow, spring‑assisted design where the disc moves linearly within the flow path. This eliminates the long travel distance and hinge inertia of swing checks, delivering extremely fast, quiet, non‑slam closure. Because the disc is always in a controlled, centered position and begins to close the instant flow decelerates, nozzle checks generate significantly lower pressure spikes. ValvTechnologies supplies high‑performance nozzle check valves engineered for severe‑service and high‑velocity applications where water hammer control is critical.
- Swing check valves have a hinged disc that swings open with forward flow and closes when flow reverses. They’re simple and cost effective but can close slowly, making them more prone to water hammer in high velocity systems.
- Tilting disc check valves have a disc that tilts rather than swings fully open. This design reduces the disc’s travel distance, allowing for quicker closure and less potential for surge formation.
- Dual plate (double door) check valves have two spring-loaded plates that fold together when flow stops. Their compact design provides rapid closure, lightweight construction and effective control of backflow surges.
- Silent (spring-assisted) check valves differ from the designs above by using a spring that pushes the disc closed as soon as forward flow slows. In these designs, the disc is already moving toward the seat as flow slows, so when the pump trips there is far less water moving backward when the valve finally closes.
Get a Custom Check Valve Recommendation from ValvTechnologies
Water hammer problems are rarely solved with a generic valve swap. ValvTechnologies distributes spring‑assisted, non‑slam check valves that open at low differential pressures, reduce destructive water hammer, and provide reliable, metal‑to‑metal shutoff across demanding liquid, gas, and steam applications. Our severe‑service nozzle check valves provide the fastest, most controlled non‑slam closure available, making them ideal for facilities experiencing recurring water hammer events, pump‑trip issues, or vibration-induced equipment damage.
If your system has experienced noise, pipe movement or repeated component damage, our team can recommend a solution ASAP.
Speak with a ValvTechnologies specialist to explore check valve options today!