Have you ever seen it
2008-07-31

              Have you seen the valve in the picture in your home? You certainly have seen it, It appears in almost every family. In fact it is a gate valve. And how much do you know about it?               People started using the valve long time ago and now it is still in use. A Gate Valve, or Sluice Valve, as it is sometimes known, is a valve that opens by lifting a round or rectangular gate/wedge out of the path of the fluid. The distinct feature of a gate valve is the sealing surfaces between the gate and seats are planar. The gate faces can form a wedge shape or they can be parallel. Gate valves are sometimes used for regulating flow, but many are not suited for that purpose, having been designed to be fully opened or closed. When fully open, the typical gate valve has no obstruction in the flow path, resulting in very low friction loss. This feature makes the valve ideal for use in vent lines of steam retorts, where rapid venting of air is so important to proper food processing. Gate Valves should not be used in the regulation or throttling of flow because accurate control is not possible.              Gate valves are characterised as having either a rising or a nonrising stem. Rising stems provide a visual indication of valve position. Nonrising stems are used where vertical space is limited or underground.               As a kind of valves that are widely used  gate valves have many advantages. There is very little pressure loss through a gate valve. In the fully closed position, gate valves provide a positive seal under pressure. But the disadvantage is also obvious. Because they operate slowly they prevent fluid hammer, which is detrimental to piping systems. Gate Valves are prone to corrosion. 

                                                                                               The gate valve (sometimes known as a sluice valve) is usually manufactured by casting the body, the gate and the bonnet of a suitable material (brass, iron, steel or another alloy) and machining the mating and assembly surfaces, and also the stem. The body has four critical areas that must be made "to spec" for the valve to make the grade and work well. The primary area is the seat in the middle of the body of the valve. Recall that the gate slides down into the seat area and "wedges" itself in between the two seating surfaces. These are on either side of the gate when it is in the "shut" position. The planes of the seats must not skew, and their angles must be precise. The gate's seats must be comparibly precise. If the gate is to work and seal the fluid path through the valve body, here's where we need precise work. 

                                                                                                                       And now there are a number of different ones made of plastic, too. They are usually injection molded, and because of the precision of the molding process, they generally don't have to machine the parts. And the demand of these valves are increasing every year in the world market.              valves normally have flanged ends which are drilled according to pipeline compatible flange dimensional standards. Cast iron, cast carbon steel, gun metal, stainless steel, alloy steels, and forged steels are different materials from which gate valves are constructed.