Bürkert’s tips for avoiding water hammer in steam systems
The apparatus used to convey and control steam must be properly designed and maintained to avoid unnecessary energy losses and damage to equipment. PIF spoke to Ian Webster, Hygienic Processing Field Segment Manager at Bürkert UK and Ireland, to find out how to avoid the destructive problem of water hammer in steam systems.
What is water hammer in steam systems?
“Heat loss from the steam transport piping causes condensate to form and the velocity of the steam flowing over the condensate causes ripples in the water,” according to Ian Webster, Hygienic Processing Field Segment Manager at Bürkert UK.
“Turbulence builds up until the water forms a solid mass, or slug, filling the pipe. This slug of condensate can travel at the same speed as the steam and will strike the first elbow or valve in its path with a force comparable to a hammer blow. In fact, the force can be great enough to break the back of an elbow joint.
In addition, water hammer can be caused by the sudden condensation of steam which reduces its specific volume by more than 1,000 times, so when steam comes into contact with colder condensate and condenses, its volume is instantly reduced to next to nothing. This sudden reduction in volume causes the condensate inside the pipework to surge towards this point. When the converging walls of condensate crash into each other the resulting noise is called water hammer
Installing a drain pocket
“Even with the most efficient lagging, condensate will form in steam pipework, due to radiated losses to the surrounding air,” says Ian. “It is recommended to fit a drain pocket at regular intervals of 30-50m and at the base of a lift. Fitting a drain pocket and trap set before an on/off valve or control valve will remove the risk of trapped condensate being released at high velocities, which can result in valve damage and water hammer.
“As a general rule, when installing a drain pocket, it should be of the same pipe diameter as the steam main – forming “equal T’s”, up to a size of DN100. If a smaller bore drain pipe is fitted then the velocity of the condensate will allow it to skip over the drain pipe connection. In addition, the reduced volume of the drain pipe may cause it to overflow, thereby becoming another source of water hammer,” he adds.
Y-type strainers and eccentric reducers
“Y-type strainers are needed to protect expensive and process-essential equipment from damage and faults due to debris in the steam,” continues Ian. “However, installed incorrectly they are a potential source of condensate pooling and therefore, water hammer. When installed in the steam line, Y-type strainers should be installed NOT in the 'belly-down' position, but with the “belly” of the strainer in the horizontal plane – an issue Bürkert has seen on several occasions while fault finding on systems it has been called in to assess.
“It may be also necessary to reduce the pipe diameter as part of the steam system design. On steam systems, it is essential that eccentric reducers are used, rather than concentric parts, with the flat side at the bottom. Concentric reducers have a funnel-like profile and are sometimes installed by less informed engineers or when costs are being cut; however this will lead to pooling of condensate and can be a prime source of water hammer,” he concludes.
Bürkert's experience of steam applications
For any company operating a steam system, it is essential to employ properly trained personnel, or qualified contractors, to design and install modifications to any existing system. Operating a poorly maintained steam process can be costly. On the same token, making a poorly designed alteration to a perfectly adequate system can also lead be problematic.
Bürkert has considerable experience in many steam applications and can offer specific advice on selecting the correct components for most steam process designs. Bürkert's range of process control valves can also be equipped with the ELEMENT control head as part of an intelligent, decentralised control system.
In addition, Bürkert has produced a Steam Site Guide with further information on the design of steam systems. Comprising 21 pages of useful information, it includes practical examples of various calculations.
For free copies of Bürkert’s Steam Site Guide, and for information on Bürkert’s free Steam Training Courses, please contact Helen Christopher, Bürkert UK Marketing Manager: Tel: +44 1285 648 720 or E-mail: [email protected] .
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