How to prevent water hammer in your plumbing
When you suddenly turn off the water tap, you sometimes hear a "bang" sound. While it may be a minor sound, it could actually be water hammer. While it's not something you're usually aware of, it can be a major problem in factory piping.
Water hammer is a phenomenon that causes great pressure to build up inside the pipes, and if left unchecked, it can cause serious damage to the pump and pipes.
This time, we will explain why water hammer occurs and what measures can be taken to prevent it.
1. How water hammer occurs
Water hammer is a phenomenon in which the speed of the fluid flowing through a pipe changes suddenly due to the rapid opening and closing of a valve, causing the pressure inside the pipe to rise and fall, resulting in a large impact. It is also known as water hammering.
■ How it occurs
There are two factors that cause water hammer: pressure fluctuation and water column separation.
For example, when you suddenly close a lever-operated water faucet, you may hear an impact sound. This is water hammer caused by pressure fluctuations. When the water in the water pipe has nowhere to go, the kinetic energy of the water changes into pressure energy, causing an impact in the pipe and making a sound.
When a pump is suddenly stopped, the flow supplied from the pump cannot keep up with the fluid that continues to move forward due to inertia, causing a sudden drop in pressure and the creation of a gas layer due to flashing (evaporation).This is called water column separation, and when the movement of the fluid in the pipe stops and the pressure is restored, the water columns collide, causing an impact.
■ Effects of water hammer
If you only hear a buzzing sound coming from a household plumbing system, it's not a big problem, but if you hear loud impacts or vibrations coming from the pipes in a factory, you should be careful.
The impact of water hammer is proportional to the flow rate and density of the fluid flowing through the pipe, so as the pump output increases, the shock wave can reach several MPa. This is extremely dangerous as it can damage measuring equipment in the pipe or even cause the pipe itself to burst.
2. Tips for preventing water hammer (piping)
Here we will introduce some tips for preventing water hammer by making some adjustments to your piping.
First, check the maximum flow rate stipulated for the pipe diameter. If there is a risk that the fluid will exceed the maximum flow rate, it is safer to change to a pipe diameter that is one size larger, referring to the table below.
Reducing the flow rate prevents rapid changes in flow rate, reducing the risk of water hammer caused by pressure changes.
Additionally, installing a surge tank in the pump discharge piping can supply fluid before water column separation occurs, reducing the likelihood of water hammer.
3. Key points to prevent water hammer (valves)
Installing appropriate valves for your piping system is also an effective way to prevent water hammer. Let's take a look at valves that are effective in preventing water hammer.
■ Avoid valves that open and close suddenly
Water hammer occurs in lever-type water pipes because the water flow changes more suddenly than in rotary faucets, and the same is true for valves installed in the pipes.
The risk of water hammer can be reduced by avoiding butterfly valves and ball valves that open and close suddenly and using valves that open and close slowly. Examples of valves that can gently control the flow rate include globe valves and gate valves.
■ Use a check valve
Check valves, also known as non-return valves, are primarily used to prevent backflow of fluids. Installing a wafer (wing) or disc type check valve at the rising point of a liquid pipe can prevent backflow water hammer.
However, even though they are all check valves, swing, ball, and lift type valves are not effective in preventing water hammer, so care must be taken.
■ Install air vent valves and relief valves
Installing an air vent valve and a relief valve is also effective.
By installing an air vent valve at a high position in the piping to create an air passage, air will flow in through the valve when water column separation occurs in the piping, preventing sudden changes in pressure.
Relief valves also release pressure when excessive pressure occurs in the piping. Therefore, when installed on the discharge side of a pump, they automatically adjust the pressure in the piping, minimizing damage to the piping and pump.
4. Tips for preventing water hammer (pump)
Water hammer is triggered by a sudden change in pressure, so it can also occur when a pump is started or stopped suddenly.
By attaching a flywheel (inertia wheel) to the pump, the pump will rotate slowly using inertia and gradually stop, thereby reducing sudden changes in pressure.
５．まとめ
Water hammer is an impact caused by a sudden change in pressure inside a pipe. If it occurs in pipes operated under high pressure and large flow rates, such as in a factory, it can cause serious damage to the pump and pipes.
To prevent water hammer, in addition to taking measures such as increasing the size of the pipes and installing check valves, air vent valves, and relief valves to avoid valves that open and close suddenly, it is also effective to attach a flywheel to the pump.
