21. A : The most likely cause is a condition known as " water hammer ." 22. A . Water hammer is another old story, and can occur wherever there is plumbing. 23. The principle is the same as in the water hammer effect so well known to plumbers. 24. :1 ) Find a way to start up the system gradually, to reduce the water hammer . 25. There is also water hammer ( banging ). 26. Their orders were to aim for near misses to create water hammer shock waves against the hull. 27. The clunk is water hammer , not only annoying but it can break the pipe at a joint. 28. Manually operated ball valves can be closed quickly and thus there is a danger of water hammer . 29. A water hammer is caused by pressure changes in pipes as water flow is stopped and started. 30. Suggestion : Knocking sounds associated with water-supply pipes are usually caused by what is called a water hammer .
