Types of Valves That Can Cause Water Hammer
The types of valves that can cause water hammer are any fast-closing valve that can induce water hammer, even in residential buildings. The rapid closure of valves causes pressure waves that occur in the internal piping when taps and valves are suddenly shut off. This extremely high pressure can lead to serious damage to the internal networks. You can read more about the risks of water hammer here. Water hammer can occur in both cold and hot supply lines.
Water Hammer in Pumping Stations
Many significant cases of water hammer that require study and analysis arise from the sudden stoppage and startup of pumps and associated valves in pumping stations.
In the normal case, the valve is opened gradually after the pump starts. And is closed gradually before the pump is stopped, and no significant risks arise in this case. However, in emergency situations where the pump suddenly stops working, such as during a power outage, the water hammer phenomenon occurs, generating a low-pressure wave that propagates towards the pipe outlet, only to be reflected back as a high-pressure wave. This can cause damage to the pump and associated equipment, as well as to the discharge pipe connected to the pump.
Water Hammer in Pumping Systems
Water hammer can occur in pump discharge pipes when the pumps stop working. Also, the closure of a valve in one of the pipelines can cause water waves and high pressures near the pump, and negative pressures can also cause water hammer.
Indicators to Assess the Need for Water Hammer Protection
There are several indicators that can determine whether the water hammer pressure can reach a value that makes a detailed water hammer study an urgent necessity to avoid its severe damages. These indicators can be classified in the following questions:
- Is there a high point in the pipe route where a vacuum and separation of the water column can occur upon shutdown?
- Is the pipe length less than 20 times the pumping head?
- Does the water velocity in the pipes exceed 1.2 m/s?
- Is the safety factor for the pipes less than 3.5 times the operating pressure?
- Does the check valve close in a time shorter than the critical period of the pipe?
- Are there fast-acting automatic valves that can open and close in less than half a second?
- Will the pump or its driver be damaged if the rotation reverses from its normal direction? And what is the maximum speed they can withstand if the reversal is possible?
- Does the pump stop before the check valve is fully closed?
- Is there a fast automatic closure used in the pumping station that does not work in case of a power failure?
- Does the pump start with the discharge valve open?
If the answer to any of the first six questions is yes. There is a high probability that the water hammer effect will be significant. The facility needs a serious study. If the answer is yes to two or more questions. The water hammer is likely, and the probability increases with the number of yes answers. In this case, prompt action must be taken to find the appropriate solution for the pumping station.
