Each failure means disruptions in the proper operation of the system and costs associated with purchasing the necessary parts and carrying out repairs. Of course, in most situations, the failure is a matter of chance. However, there are many risks that can be avoided with proper care and planning. In the case of water supply installations and all water systems, one of the basic threats is the occurrence of the so-called water hammer. As research shows, this phenomenon is responsible for almost 80% of all failures occurring on water supply network cables not equipped with safety devices. But what is water hammer? What is the cause? And what to do to prevent it? We answer these and other questions in our article.
Water hammer - theoretical basis of the phenomenon
Water hammer is a term used to describe a sudden increase in pressure caused by an unplanned, rapid and forced change in the flow rate in a pipeline in a short period of time. The name of the phenomenon itself comes from the characteristic sound that occurs during the process and which resembles hitting with a hammer. According to a specialized definition, water hammer is "caused by the inertia of a mass of liquid moving in a pipeline, the flow speed of which changes suddenly." Moreover, "a sudden change in the speed and volume flow of the flowing liquid causes a local change in the share of kinetic and potential energy in the total energy of the cross-section, expressed by an increase or decrease in pressure in the stream. In conditions of a very rapid deceleration of the stream speed, there is a sharp drop in kinetic energy, which causes an increase in potential energy, which is expressed in a large increase in pressure."
Depending on the nature of the phenomenon, we may be dealing with positive water hammer (pressure increase) or negative water hammer (sudden pressure drop). Regardless of the type, water hammer can cause many problems, including: such as:
- destruction of the pipeline,
- damage pumps,
- engine damage,
- damage to check valves,
- interruption of the flowing water stream.
What are the causes of the problem?
Which causes it to become the negative phenomenon it is water hammer? There may be many reasons, but practice shows that two main aspects are:
- a situation where the non-return valve on the pipe from the pump is installed more than nine meters above the water table,
- a situation in which a non-return valve installed on the pipeline from the pump is leaking, and another non-return valve installed above the previous level remains tight.
Other causes that can lead to problems include:
- failures such as pipe breakage, sudden blockage of the pump, twisting of the spindle or breaking of the thread of the valve, vibration of deformed elements,
- the phenomenon of cavitation, which is caused by excessive water flow speed, large difference in pressure level to the value of the liquid evaporation pressure at a given temperature, closing of the gate valve or high location of the network point,
- accidental events, including a sudden interruption in electricity supply, change in initial flow conditions, change in junction outflows, change in water level in initial or intermediate network reservoirs,
- improper operation of the system, manifested as sudden shutdown of all pumps feeding the pipeline, incorrect closing or opening of gate valves, improper maintenance and repairs,
- vibrations related to uneven operation of pumps or operation of float valves.
But that's not the end. Another cause of the problem may be the use of incompatible solutions, such as inserting a new one with a smaller diameter into the old pipe (this results in an increase in the speed of the flowing liquid). It is worth remembering that any changes may lead to unplanned damage, so new solutions should be selected depending on the characteristics of the analyzed system.
How to prevent?
Importantly, water hammer and the related problems can be prevented. Some of the ways are:
- selecting the correct cross-sections and safety devices, selecting appropriate valves and gate valves, as well as counteracting the phenomenon of resonance,
- an attempt to eliminate the phenomenon of water hammer by directly changing the system configuration, including modifying the route, pipe lengths, diameters, pipeline material, connections, or bypasses,
- introducing various devices and mechanisms into the system that cause the liquid to be dropped from the pipeline or kept in a certain space outside the system; this means the use of water-air tanks, water-air tanks with a differential orifice installed on the drain, aeration valves or safety valves.
