A waterhammer is a pressure surge created due to sudden stop and/or start of a liquid flow in a piping or pump system. It is usually resulted from abrupt change in liquid flow rate due to the sudden start or stop of pumps, or even sudden closure of valves. Most liquids are in compressible which means no matter how much pressure is applied, the volume does not change. When a liquid comes to a halt, it undergoes a momentum change, producing a shock wave that travels back and forth in an isolated system. Since in compressible liquids have a lack of “springiness”, sudden change in momentum can cause high pressure surge in pipes which could lead to catastrophic failures of pipe systems. It can cause damage to pipe supports, leakage at bends or even cause pipes to burst.
In a piping network, slight water hammer can be detected by:
- Pipe movements
- Banging noises
- Pulsing flow
Serious waterhammer gives the same effect but these might be large enough to cause serious damage. Pipe systems that show the characteristics that can lead to serious water hammer should be analyzed by computer software, especially if hazardous chemicals flow through the pipes.
One of the primary causes of water hammer is the sudden closure of a valve in piping/pump system. Figure 1 below shows a pump pumping liquid at a constant flow rate across a fully open valve through a check valve. The check valve serves as a protection for the pump from a reversal flow.
Figure 1: Simple schematic of piping system
When valve 1 at the end of the network is set to close instantly, the liquid flowing from the pump strikes the closed valve creating a change of momentum. When the flow ceases, all of its kinetic energy of motion is converted into pressure energy. Since the energy produced by the liquid comes to a sudden halt due to closure of the valve, the liquid could not pass through the closed valve. The pressure or shock wave generated will travel along the path of least resistance, which in this case, is back upstream. The wave hits the upstream valve (i.e. check valve), forcing the valve to close, to prevent back flow to the pump. The liquid will be isolated between the two valves and the wave will be reflected back and forth until friction and reflection losses cause the wave to diminish. A common example of waterhammer effect that occurs every day, is simply turning off a shower in most homes, which quickly sends a loud thud through the house. This is a perfect example of a water hammer.
Waterhammer problems can be either solved by mitigating its effects or preventing its occurrence. There are numbers of mitigation of waterhammer , however, prevention is often the better strategy.
Solutions to waterhammer depend on the circumstances of each situation. They can include the following:
- Reduce the pumping velocity which could be done using a larger pipe diameter or lower flow rate.
- Selecting a stronger pipe by selecting higher design pressure pipe specification.
- Controlling valve closure time.
- Installing a pulsation dampener to prevent damage caused by pulsation which generally occur when a liquid’s motive force is generated by a positive displacement pump.
It is better to model the system using suitable software, so that any potential for water hammer problems can be revealed and solutions can be studied in the model to enable designer or engineers to select the best and most cost effective solution to a pipe system. There are several software programs, including PIPENET, Flowmaster, HiTrans, Hammer, and Wanda which are capable in performing a waterhammer analysis.
Waterhammer can be a serious issue, which can cause catastrophic failures in a piping system of a plant. By identifying the potential cause and analyzing the system beforehand, engineers or operators can avoid situations that have the potential to cause waterhammer during a specific process, avoid damaging equipment, prevent failing of valves and disallow costly downtime.
- Predicting Pressure Surge
- Minimize Potential Waterhammer Occurrence
- Efficient & Cost-Effective Pressure Surge Mitigation Strategy
Further investigation on the water-hammer control branching strategy in pressurized steel-piping systems (2018) Available here: https://doi.org/10.1016/j.ijpvp.2018.06.002