3553 -- Investigating the Causes of Water Hammer in a Water Control Valve PDF

Investigates a water flow control valve. The flow rate of the water is regulated by the pressure of a stationary fluid acting on a bellows connected to the valve stem. A typical application of these valves is to control the water flow through a water-cooled refrigerant condenser in a refrigeration system, using the refrigerant pressure to regulate the water flow rate. In some valves, an effect known as "water hammer" occurs when the refrigerant pressure is in a certain range. Water hammer is a series of sonic shocks produced by suddenly reduced liquid flow in rigid (metal) pipes (Avallone and Baumeister 1978). Water hammer manifests itself by a low-frequency oscillation of the valve stem. The result of the water hammer is a very noisy valve and a pulsating water flow. The dynamic behaviour of a system consisting of the valve and the upstream and downstream connecting pipes is analysed using a finite time step approach. The analysis was written into a Fortran computer program to compute the valve gap, flow rate, and pressures in the system. From the simulation, it was found that the relationship between the friction factor and the Reynolds number for the flow through the valve gap has a significant effect on the results. Based on these results and experimental data, it appears that for valves exhibiting water hammer, the flow through the valve gap is marked by abrupt changes from laminar to turbulent flow. Three different possible design modifications that may reduce or eliminate the water hammer are presented. By changing the dimensions of the valve, the water flow in the valve gap should be in a different Reynolds number range. The second alternative is to attempt to change the flow characteristic around the circumference of the valve gap. Finally, introducing more damping will prevent the oscillations associated with water hammer.

KEYWORDS: water hammer, fluid flow, valves, water flow, refrigeration, condensers, water cooled condensers, regulating, computer programs, calculating, Reynolds numbers