The manual valves are control component in the pipeline fluid delivery system. They are used to change the passage section and the flow direction of the medium and have the functions of diversion, cutoff, regulation, throttling, check, diversion, or overflow relief.

Manual valves are divided into four groups according to the way the closure member moves onto the seat. Each valve group consists of a number of distinct types of valves that, in turn, are made in numerous variations.

• Stopper type closure—globe, needle

• Vertical slide—gate

• Rotary type—ball, plug, butterfly

• Flexible body—diaphragm

The way the closure member moves onto the seat gives a particular group or type of valve a typical flow-control characteristic. This flow control characteristic has been used to establish a preliminary chart for the selection of valves. The final valve selection may be made from the description of the various types of valves and their variations that follow that chart.