CONTROL VALVES FOR STOCK AND WHITE WATER - REDUCING CAVITATION DAMAGE BY SPECIFYING THE CORRECT SIZE

Control valves throttle the flow of pulp stock and white water and must be specified properly to minimize pumping costs and valve maintenance. To select stock valves, the engineer needs the correct sizing factors for various consistencies and types of stocks. In order to predict the pressure losses, more accurate data are needed. Recent laboratory studies at Oulu University in Finland show that pulp stock at a consistency of 2% and greater cushions the implosions of water vapor, or cavitation. Damage to the control valve and downstream piping is less of a problem than it is for white water and thin stock. This work has led to two new variations of the V-ball type of pulp stock control valve to handle these problems. Accurate new sizing coefficients for stock of 14-16% consistency have been produced and incorporated in a new computer program for sizing control valves. This program will help to improve the accuracy of sizing calculations and make control valve installation more cost effective.