The origin of water hammer

Ziruba Josef. Water Hammer in Pipe-Line Systems. Elsevier, 1993, English, 363 pages.

Источник: http://www.twirpx.com/file/87516/

Let us consider a pipe-line, or a pipe-line system, filled with a flowing liquid. The system may contain various devices, such as valves, pumps, reservoirs, surge tanks, air inlet valves, etc., all of which may affect the flow. The flow of liquid in a system may be steady or unsteady. At steady flow, the fundamental values defining the flow do not vary with time. From the point of view of the problem discussed, a flow in which pressure and velocity vary irregularly due to turbulence is also steady. At unsteady flow, its fundamental values vary with time.

The pressure of a liquid in a conduit and its discharge are interdependent.

Every change in discharge induces a corresponding change in pressure and vice versa. The changes in pressure caused by this dependence are called water hammer. In the present work, this term is used, for the sake of simplicity, also for cases, where the flowing liquid is not necessarily water, but may be any liquid having similar properties, possibly with an admixture of solid substances, or gases.

The changes of pressure at water hammer may be insignificant, but could also be large, sometimes leading to the rupture of a pipe-line, or of other devices forming part of the pipe-line system. Such breakdowns are by no means rare.

Another danger of water hammer is the difficulty of estimating in advance, without detailed calculations, whether the water hammer imperils the system in a specific case, or whether its effects can be neglected. Such calculations are laborious, especially for more complex hydraulic systems; they require expert knowledge and such information about the system under consideration as may not always be available.

The problem of water hammer may be important in the design and operation of various types of hydraulic systems, such as water-supply networks, irrigation systems, industrial conduits, distribution systems, cooling circuits of thermal and nuclear power stations and many other hydraulic installations in various branches of industry. Unsteady flow develops in all these systems, at least during their opening and closing, and is inevitably accompanied by water hammer, even if this may not be dangerous in every instance.

Water hammer may be the cause of other adverse effects besides an increased mechanical stress of the pipe-line and the attached equipment. It may affect the regulation of hydraulic systems or distort the results of measurements of hydraulic quantities.

On the other hand, the effect of water hammer is exploited in some devices: the hydraulic ram may serve as an example of such an application. It is a simple machine by means of which water can be pumped to considerable heights.