Every engineer who suffered from "water hammer" will read this article again and again!

Dry water treatment people get together to discuss the problems encountered in the project most. Recently, they have talked more about:

Water hammer effect, in the pressure pipeline, due to some external reasons (such as the sudden closure of the valve, the sudden stop of the pump unit), the water velocity changes suddenly, resulting in water hammer. This kind of hydraulic phenomenon is called water hammer or water hammer.

We will analyze the case, bring you some solutions to water hammer phenomenon, and help you strengthen the basic technical skills through systematic experience sharing, so as to become an expert in solving problems in engineering.

01   Be careful, water hammer happens frequently

(1) When the valve is closed too fast, the follow-up water flow will reach the maximum quickly under the action of inertia and produce destructive effect, which is the "water hammer effect" in fluid mechanics, that is, positive water hammer.

(2) When the closed valve suddenly opens again, it will also produce water hammer, which is called negative water hammer. It also has certain destructive power, but it is not as big as the former.

(3) The sudden power failure or start-up of the electric pump unit will also cause pressure shock and water hammer effect. The shock wave propagates along the pipeline, which easily leads to local overpressure of the pipeline and causes pipeline rupture and equipment damage.

(4) The water pipeline is too long, the height difference is too large, and the water flow velocity in the pipeline is too large.

02

We should pay attention to the harm of water hammer

The local pressure rise caused by water hammer can reach several times or even dozens of times of the normal working pressure of the pipeline. This kind of large amplitude pressure fluctuation mainly causes harm to the pipeline system

1. Strong vibration of pipeline and disconnection of pipeline joint are caused;

2. The valve was damaged, and the serious pressure was too high, which caused the pipe burst and the pressure of water supply network decreased;

3. If the pressure is too low, it will lead to the collapse of the pipeline and damage the valve and fixing parts;

4. It can cause the pump reverse, damage the equipment in the pump room, seriously cause the pump room submergence and other accidents, and affect the production and life. In the membrane project, when it is serious, it will crush the membrane components and bring irrecoverable losses.

Therefore, the solution and protection of water hammer effect has become one of the key technologies in water treatment engineering.

03

To learn, look at the solution from the case

Due to the space problem of a project site, the ultrafiltration membrane was installed horizontally. There are many problems, such as cracks at both ends, leakage and so on.

Final cause: it was found that the exhaust was not clean at the moment of opening the pump and valve, resulting in water hammer and air hammer.

Solution: each end cover is equipped with an exhaust valve, and the inlet valve is changed from pneumatic to electric slow opening valve.

To sum up the solution of "water hammer phenomenon", we should pay attention to "prevention first, prevention first"

1) High pressure pump adopts soft start mode to avoid, such as step-down start, variable frequency speed control start and series resistance start with automatic controller.

2) Avoid in the operation mode, such as closing or turning down the inlet valve when starting, and then slowly opening the valve until it reaches the working pressure of the system.

3) Use control to avoid, such as using PLC to control an electric slow door, open the valve in dozens of seconds.

4) For example, a return pipe is set at the concentrated water discharge outlet to make the highest point of the pipe exceed the highest pressure vessel in the reverse osmosis device, so that the pressure vessel will be full of water when the device stops running