Pressure Surges are one of the least understood hydraulic phenomenon in water and fluid piping systems. Yet, with or without direct understanding, unharnessed pressure surges can cause extensive damage to pipes, valves, pumps and other connected equipment. In extreme cases, pressure surges have cause personal injury and even have caused lose of life.
The good thing about pressure surges is that there are industry professionals who specialize in understanding surges and the cause of pressure surges. Often, the cause of a pressure surge can be an inexperienced operator or a malfunctioning control valve. One common factor in nearly every surge condition is a “rapid change in fluid velocity”. This can often be due to a rapid valve closure or a “pump trip” due to a power outage or control malfunction.
In most cases, surges cannot be completely eliminated, but with a detailed hydraulic review and selection of specialized equipment, the results after a surge condition can be significantly reduced to a point where the surge itself is merely an incident that changes system dynamics, but there is no resulting damage to the pipeline or equipment.
There are many products in the fluid piping industry that can help to reduce certain surge events. These include air valves and certain types of check valves and pressure relief valves. However, due to the velocity of pressure transients (up to 2000 FPS), most of these components are merely a means to help reduce the routine “pressure peaks” caused by pumping operations.
Catastrophic damage is more often the result of a “pump trip”, often the result of the loss of power. In systems that experience a pump trip, the fluid velocity changes can create negative pressures and fluid column separation. In these dangerous situations, air valves, check valves and pressure relief valves cannot “add fluid energy” to the system. These components are helpless in terms of maintaining a positive pipeline pressure at the focal point of the surge. The greatest point of damage is typically where fluid column separation occurs and when the two fluid columns accelerate and collide, they create extraordinary surge pressures that often result in catastrophic piping failure and extensive damage to surrounding equipment.
Many water utilities have surge problems daily; these surges can be associated with routine operations of pumps, control valves, and system operations. When surges occur often enough, they become almost expected merely by the frequency in which they happen. We would remind water system managers and operators that pressure surges can cause catastrophic damage and personal injury. Pressure surges have been the focus of detailed engineering study and the affects of pressure surges can be mitigated effectively.
While catastrophic surge events may not be a common event in your piping system, it would be prudent for utility owners and managers to contact their consulting engineer to discuss the potential surge issues in their system. A low head system is even more likely to have damaging results as a result of a pressure surge event. Remember that it only takes one “perfect hydraulic storm” to change your sense of priorities in proactively addressing potential pressure surge problems.
Harper Control Solutions is an industry leader in surge control equipment. Charlatte America specializes in surge analysis and is the world leader in Bladder Surge Tanks up to 40,000 gallon tanks. Each system has unique characteristics and therefore it is always a good practice to have a hydraulic model the system and a comprehensive surge analysis. Cla-Val Anticipating Surge Relief Valves can sometimes be an effective means to reduce damage to piping and connected equipment. Before we recommend any solution to a surge problem, we start by a comprehensive review of the hydraulic model of the system.
Harper Control Solutions works with owners and consulting engineers in review of the system design and can provide a hydraulic surge analysis of the system.