How to calculate/select size and flow capacity of an anti-surge control valve

One of the used control application in the compressor industry is the anti-surge control loop. The aim of this control loop is to avoid that the compressor works on the surge line. The paper proposes a method to calculate/select the optimal size of an anti-surge control valve. The basis of the method is the tolerated value of the velocity/Mach No. at the valve output. Further criteria are: accepted min. allowance factor, accepted maximum sound level and avoidance of choked flow. Part 1 is dedicated to the calculation of valves with 2 stages trim, Part 2 to the calculation of valves with 3 or 4 stages trim. Each part contains a calculation example.