Dewrance Pumping Control Valves
These valves are designed to bypass high pressure feedwater around a group of heaters in the event of high water level in the shell caused by a defective tube, weld or drain system. The time available to give protection to a turbine in modern feed systems is short but these valves can operate in approximately 5 seconds in a 300mm bore pipe system with the minimum of hydraulic shock. Protection is achieved in the system by installing fast closing tee and changeover valves in the pipework around a heater or group of heaters. These valves are equally applicable in new or established stations. The motive power employed is the feedwater pressure and the system is designed to ‘fail safe’ in that the heaters will be by-passed if either electric or pneumatic supplies fail. As an alternative to the medium operated valves, a spring loaded bypass valve can be supplied. This is the simplest form of bypass which relieves at a set pressure and is fail safe. The Dewrance design has the advantages of a pressure seal bonnet and external spring adjustment whilst the valve is still under pressure.