Making the right choice

摘要

DAMIEN MORAN, FIELD SEGMENT MANAGER, HYGIENIC, PHARMACEUTICAL AT BURKERT, LOOKS AT SOME OF THE BASIC DIFFERENTIATORS OF PROCESS VALVES AS WELL AS SOME RECENT DESIGN DEVELOPMENTS. Control valves are used to manage the flow rate of a liquid or a gas and in-turn control the temperature, pressure or liquid level within a process. As such, control valves are defined by the way in which they operate to control flow and include globe valves, angle seat, diaphragm, quarter-turn, knife and needle valves, to name a few. In most cases the valve bodies are made from metal; either brass, forged steel or in hygienic applications 316 stainless steel. One of the main areas of debate when specifying control valves is determining the size of the valve required. Quite often process engineers will know the pipe diameter that is used in an application and it is tempting to take that as the defining characteristic for the control valve. Of greater importance are the flow conditions within the system as these will dictate the size of the orifice within the control valve. The pressure either side of the valve and the expected flow rate are essential pieces of information when deciding on the valve design. Improving efficiency. Inside the valve body, the actuator design is predominantly either a piston or a diaphragm design. The piston design typically offers a smaller, more compact valve which is also lighter and easier to handle than the diaphragm designs. Actuators are usually made from stainless steel or polyphenolsulpide (PPS), which is a chemically resistant plastic. The actuator is topped off by the control head or positioner.