Water hammer is a high-pressure surge or wave created by the kinetic energy of moving fluid when it is rapidly forced to stop or change direction, altering the liquid’s velocity. Rapid stopping or starting or changing of direction of an incompressible fluid like water or oil in a system is caused by a variety of valves or pumps.
It is a myth that a pressure spike cannot exceed the normal pressure in the system. The fact is that pressure spikes can reach up to eight times the system pressure. Even though they may last only milliseconds, the potential damage can be lasting. Pressure gauges and transmitters fitted to measure normal line pressure at the receiving end of these pressure spikes are often irreparably damaged if not suitably protected.
One of the main concerns of hydraulic and other system designers is how to eliminate or minimise water hammer. Methods and formulas for calculating water hammer pressures are freely available online.
How water hammer affects pressure gauges and transmitters
Pressure gauges and transmitters are designed to measure pressures up to the full-scale value of the instrument. For short periods, these instruments may accept an overpressure of a percentage of the rated full-scale pressure without permanent damage.
The measuring sensors of pressure gauges (bourdon tube) and transmitters (diaphragm) are normally manufactured from a flexible elastomeric type of material to ensure accuracy and repeatability.
Good quality pressure gauge bourdon tubes are designed, manufactured and tested to withstand up to 1,3 times the rated pressure in normal pressure gauges for short periods. In the case of some diaphragm-operated pressure gauges that do not use bourdon tubes (but with a limited range of 2500 kPa maximum) these can handle up to five times more, without permanent damage to the instrument.
Most pressure transmitters can withstand 1,5 to two times the rated full-scale value for short periods, without permanent damage. Pressure spikes exceeding these limits can cause the elastomeric sensors to deform permanently, making them unable to return to zero. Accuracy and repeatability may be affected, and in extreme cases rupturing of the sensor may occur.
Gauges are sometimes returned to the manufacturer for investigation, completely over-pressured, and often with a ruptured bourdon tube. When SA Gauge informs the customer of the gauge’s condition, they often get responses such as: “But how can it be possible? This is a 1000 kPa gauge and the pump can generate a maximum of 600 kPa.” Water hammer is the most likely cause of damage in such a scenario.
Protecting against water hammer
The progression of the water hammer shockwave needs to be detained and slowed before reaching the instrument sensor.
SA Gauge manufactures several such devices in order to achieve this. The most common and economical is a simple threaded snubbing screw that screws into the process connection of the gauge, restricting the pressure port to minimise flow into the gauge. In severe cases, a length of small-bore capillary tube is attached to the snubber to increase the effectiveness. Other devices like external adjustable flow restrictors, piston type snubbers, and needle valves are also available to choke the offending pressure surge to an acceptable level.
It is important to note that these devices will not protect the instruments against sustained overpressure, which will still damage the instruments. An overpressure protector will be required in these cases.
Pushing technological boundaries with Festo Electric Automation solutions Festo South Africa
Editor's Choice
In the ever-evolving landscape of Industrial Automation, Festo Electric Automation solutions are at the forefront of a revolution, fundamentally reshaping production paradigms. As a global leader in automation, Festo focuses on intelligent connectivity to reduce costs, save time, and increase efficiency and convenience for customers.
Read more...Perfect balance for every race Horne Technologies
Editor's Choice Electrical switching & drive systems & components
It goes without saying that success in Formula 1 requires a top driver. However, their chance of achieving a place on the podium depends on the car, which in turn depends on three essential factors: engine, tyres and aerodynamics. To find the optimum balance, the racing teams test models of their bolides in the wind tunnel. At Sauber, the adjustable components are moved on the model and in the test chamber using FAULHABER motors.
Read more...MeerKAT radio telescope array
Editor's Choice News & events
Leading consulting engineering and infrastructure advisory practice, Zutari is continuing its involvement with the world-leading MeerKAT radio telescope array, where it has played a leading role since the project first broke ground.
Read more...Top 10 emerging technologies
Editor's Choice
The World Economic Forum (WEF) has identified ten technologies likely to make a significant positive impact in the next three to five years. These are detailed in the ‘Top 10 Emerging Technologies’ report, which explains each technology’s potential for addressing global challenges and the factors that will shape the future and revolutionise connectivity still further.
Read more...Electrifying the future Parker Hannifin - Sales Company South Africa
Editor's Choice Electrical switching & drive systems & components
A revolution is underway, transforming the way we power compact construction machines and heavy-duty mobile machinery. This is the electrification of equipment, a movement propelled by the need for environmental sustainability, lower emissions, reduced noise levels, and the pursuit of a cleaner, greener future.
Read more...How to clean compressed air effectively
Editor's Choice
SO-Reliability Partners has taken another step in bringing to market highly effective solutions to combat contamination in all its forms. The locally designed and patented Air Wizard inline water trap is proudly manufactured in South Africa. It has been SABS tested for the separation of water, oily fluids, rust and solid particulates from pneumatic compressed air or gas lines.
Read more...New Black Bruin hydraulic motors for heavy-duty applications Axiom Hydraulics
Editor's Choice Hydraulic systems & components
Axiom Hydraulics and Black Bruin have been working together since the late 1990s, serving southern Africa’s fluid power, mining, industrial, agriculture and marine industries. Now Black Bruin is extending its rotating shaft motor portfolio. With a patent pending design, the new X-series is engineered to enhance the performance of both new and existing machinery in terms of durability, serviceability and cost-effectiveness.
Read more...Quality gearboxes for agriculture SEW-EURODRIVE
Editor's Choice Electrical switching & drive systems & components
Offering a complete gear solution for centre pivot irrigation systems, SEW-EURODRIVE brings its quality products and support as an original equipment manufacturer (OEM) closer to South Africa’s farming sector.
Read more...Robotic solution for adhesive tape application with flexible control Beckhoff Automation
Editor's Choice Robotics & Mechatronics
In industry, even elaborate processes, such as the application of adhesive tape to parts with varying geometries are automated. Innovative Automation has developed a platform with Beckhoff control technology and a remote feeding module, which increases productivity and enables flexible customisation for different requirements.
Read more...The information explosion
Editor's Choice Other technologies
The world has a data storage problem. There’s an explosion in the volume of data being generated and stored, and it’s rising exponentially. Fortunately, organisations are beginning to test new storage technologies like DNA storage, glass storage, neuromorphic computing, and extreme parallelism in order to keep up.
printer friendly version