Definitions And Classifications

Multi-Turn or Linear Motion Valves are broken into five different types:  gate, globe, pinch, diaphragm, and needle.

Gate valves are used in general service for on and off non throttling service. A flat face, vertical disc or gate that slides down through the valve are the methods the gate valve used to block the flow.

A plug with a flat or convex bottom lowered onto a matching horizontal seat located in the center of the valve is how the globe valve works. The valve opens by raising the plug to start the fluid flowing.

Slurries or liquids with large amounts of suspended solids use pinch valves.  This type of valve seals by means of one or more flexible elements, such as a rubber tube, that can be pinched to shut off flow.

A diaphragm valve closes with a flexible diaphragm attached to a compressor.  When the compressor is closed, the diaphragm seals and cuts off the flow.  This type of valve handles corrosive, erosive, and dirty jobs.

The needle valve controls volume by restricting flow in small lines.  The fluid going through the valve turns 90 degrees and passes through an orifice that is the seat for a rod with a cone-shaped tip.  The size of the orifice is changed by positioning the cone in relation to the seat.

Quarter Turn or Rotary Valves come in three types:  plug valve, ball valve, and butterfly valve.  All three types of valves are used for on-off service and throttling service.

The plug valve controls flow by means of a cylindrical or tapered plug with an opening in the center that lines up with the flow path to permit flow.  A quarter turn in either direction blocks the flow path.  Many types and styles of plug valves are used throughout the process industry:  lubricated, nonlubricated, rotor, and eccentric.