VALVE FUNCTIONS AND BASIC PARTS
Introduction to the Types of Valves
Because of the diversity of the types of systems, fluids, and environments in which valves must
operate, a vast array of valve types have been developed. Examples of the common types are
the globe valve, gate valve, ball valve, plug valve, butterfly valve, diaphragm valve, check valve,
pinch valve, and safety valve. Each type of valve has been designed to meet specific needs.
Some valves are capable of throttling flow, other valve types can only stop flow, others work
well in corrosive systems, and others handle high pressure fluids. Each valve type has certain
inherent advantages and disadvantages. Understanding these differences and how they effect the
valve's application or operation is necessary for the successful operation of a facility.
Although all valves have the same basic components and function to control flow in some
fashion, the method of controlling the flow can vary dramatically. In general, there are four
methods of controlling flow through a valve.
Move a disc, or plug into or against an orifice (for example, globe or needle type
Slide a flat, cylindrical, or spherical surface across an orifice (for example, gate
and plug valves).
Rotate a disc or ellipse about a shaft extending across the diameter of an orifice
(for example, a butterfly or ball valve).
Move a flexible material into the flow passage (for example, diaphragm and pinch
Each method of controlling flow has characteristics that makes it the best choice for a given
application of function.