The task of finding the right valve can be daunting, and there are hundreds of valve manufacturers producing many different types of products. The key, however, is to identify your exact valve requirements. So the next time you need help specifying which valve to use, refer to this guide.
MULIT-TURN VALVES OR LINEAR MOTION VALVES
The Gate Valve
The gate valve is a general service valve used primarily for on-off, non-throttling service. The valve is closed by a flat face, vertical disc, or gate that slides down through the valve to block the flow.
The Globe Valve
The globe valve effects closure by a plug with a flat or convex bottom lowered onto a matching horizontal seat located in the center of the valve. Raising the plug opens the valve, allowing fluid flow. The globe valve is used for on-off service and handles throttling applications.
The Pinch Valve
The pinch valve is particularly suited for applications of slurries or liquids with large amounts of suspended solids. It seals by means of one or more flexible elements, such as a rubber tube, that can be pinched to shut off flow.
The Diaphragm Valve
The diaphragm valve closes by means of a flexible diaphragm attached to a compressor. When the compressor is lowered by the valve stem onto a weir, the diaphragm seals and cuts off flow. The diaphragm valve handles corrosive, erosive, and dirty services.
The Needle Valve
The needle valve is a volume-control valve that restricts 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 VAVLES OR ROTARY VALVES
The Plug Valve
The plug valve is used primarily for on-off service and some throttling services. It controls flow by means of a cylindrical or tapered plug with a hole in the center that lines up with the flow path of the valve to permit flow. A quarter-turn in either direction blocks the flow path.
The Ball Valve
The ball valve is similar in concept to the plug valve, but uses a rotating ball with a hole that allows straight-through flow in the open position and shuts off flow when the ball is rotated 90 degrees to block the flow passage. It is used for on-off and throttling services.
The Butterfly Valve
The butterfly valve controls flow by using a circular disc or vane with its pivot axis at right angles to the direction of flow in the pipe. The butterfly valve is used both for on-off and throttling services. (photo below)
The Check Valve
The check valve is designed to prevent backflow. Fluid flow in the desired direction opens the valve, while backflow forces the valve closed. (photo below)
The Pressure Relief Valve
The pressure relief valve is designed to provide protection from over-pressure in steam, gas, air, and liquid lines. The valve "lets off steam" when safe pressures are exceeded, then closed again when pressure drops to a preset level.