Valves that are used in Transportation of Fluids and Their Types

What are Valves?


"The Valves are devices that are commonly used to control the rate of flow of fluids in a pipeline, show an even wider variety than do fittings".

Types of Valves:

There are many types of Valves but I am mentioning here some of the most popular and widely used Valves that are as under:

• Plug Cocks

• Globe Valves

1. Metal Disc
2. Composition Disc

• Gate Valves 

1. Nonrising Stem
2. Rising Stem
3. Outside Screw and Yoke

• Check Valves

1. Ball Check Valve
2. Swing Check Valve

Construction & Working Detail Description:

• Plug Cocks

Plug Cocks are very important devices.They are simplest method of regulating the flow of fluids.They consist essentially of a body casting. in which fits a conical plug with a passage through it. This must, of course, be closed by some sort of packing around the stem.For example see the picture below:

Plug Cocks are universally used on small lines for compressed air, rarely for steam or water.Their disadvantage is that if the sides of the plug are too nearly parallel, the plug is easily wedged in the body so firmly that it is difficult to turn.While if the sides of the plug are tapered too much, the pressure in the line acting against this inclined surface has an upward component that tends to push the plug out of its seat. 

Most cocks tend toward the former difficulty rather than the latter, and therefore the universal complaint is that cocks are stick and hard to open. To remedy this, there are a number of special designs on the market. One of the best known of which has lubricant inserted at the stem of the cock. The lubricant is transmitted to the working faces through small holes drilled through the body of the plug. This is satisfactory for ordinary service, but in special cases it is difficult to find the greases that will not melt or be dissolved.

Another disadvantage of the cock is that when the bore is cylindrical, as is nearly always the case, the area of the opening in pipe changes very rapidly with a slight amount of rotation when the cock is just opened and changes practically not at all when the cock is nearly open. Consequently, it is difficult to regulate the flow with using Cocks, especially at low rates of flow that call for fractional openings. Cocks are usually used, where they will be either wide open or completely closed. There are available, however cocks with especially shaped openings so that the area of the opening is nearly, if not quite, proportional to the angle through which the plug is turned.