water hammer

GC: n

CT: Water hammer is a pressure surge or wave caused when a fluid (usually a liquid but sometimes also a gas) in motion is forced to stop or change direction suddenly (momentum change).
As soon as steam leaves the boiler, it starts losing heat. As a result, steam stats condensing inside the pipe work. The rate of condensate formation is high particularly during the start ups when the system is cold. As a result of the condensation, the droplets of water are formed. These droplets of condensate get built up along the length of steam pipework forming a solid slug. When this slug encounters any obstacle such as a bend, it will be brought to a halt abruptly. All the kinetic energy of the condensate slug will get converted into pressure energy which has to be absorbed by the pipe work. This gives rise to the phenomenon of water hammer.

S: FORBESM – https://bit.ly/2zLPbuj (last access: 7 December 2018)

N: 1. – water (n): Old English wæter, from Proto-Germanic *watr- (source also of Old Saxon watar, Old Frisian wetir, Dutch water, Old High German wazzar, German Wasser, Old Norse vatn, Gothic wato “water”), from PIE *wod-or, suffixed form of root *wed- (1) “water; wet.”
– hammer (n): Old English hamor “hammer,” from Proto-Germanic *hamaraz (source also of Old Saxon hamur, Middle Dutch, Dutch hamer, Old High German hamar, German Hammer). The Old Norse cognate hamarr meant “stone, crag” (it’s common in English place names), and suggests an original sense of the Germanic words as “tool with a stone head”, which would describe the first hammers. The Germanic words thus could be from a PIE *ka-mer-, with reversal of initial sounds, from PIE *akmen “stone, sharp stone used as a tool” (source also of Old Church Slavonic kamy, Russian kameni “stone”), from root *ak- “be sharp, rise (out) to a point, pierce.”
2. The impact forces reacting on piping or vessels when a flow of liquid is suddenly stopped or some other pressure wave is transmitted through the liquid.
Term officially approved by the Lexicon Project Committee (New Brunswick, Canada).
3. Presence of water hammer can be easily detected by the noise it makes. Noise is not the final effect of water hammer but just an indication of it. Water hammer has multiple adverse effects on steam systems. Water hammer can damage equipments like flow meters which are installed on the steam network. Instances of rupture and disruption of piping on account of water hammer are also quite common.
4. The destructive nature of water hammer can be realized through the following illustration:

  • Recommended velocity of saturated steam in pipe network = 20-35 m/s
  • Recommended velocity of water in pipe network= 2-3m/s

In case of water hammers, condensate is dragged by steam and hence, the water slug travels with velocity equal to that of steam which is around ten times more than the ideal water velocity. As a result, the total pressure impact exerted by water hammer is very high.
5. Though water hammer cannot be completely eliminated from steam systems, it can certainly be avoided. Some of these practices are:

  • Steam lines should always be installed with a gradual slope (gradient) in direction of flow.
  • Installing steam traps at regular intervals and also at the low points. This ensures removal of condensate from the steam system as soon as it is formed.
  • Sagging of pipes should be avoided by providing proper support. Sagging pipes can form pool of condensate in the pipework, increasing the chances of water hammer.
  • Operators should be trained to open isolation valve slowly during the start-up modes.
  • Drain pockets should be properly sized to ensure that condensate just not jumps over it. Instead, the drain pockets should be sized enough so that all the condensate reaches the trap.
  • Reducers – Eccentric reducers should be used against concentric reducers.

S: 1. OED – https://bit.ly/2G1QBWY (last access: 7 December 2018). 2. TERMIUM PLUS – https://bit.ly/2UkAJC2 (last access: 7 December 2018). 3 to 5. FORBESM – https://bit.ly/2zNMTuG (last access: 7 December 2018).


CR: cavitation, dam, expansion tank, hydraulic energy, hydraulic turbine, hydroelectric power, hydroelectric power plant, pumped-storage plant, renewable energy, weir.