The distinction between a cock and a valve is not at all definite. Custom has determined that in certain places a cock shall stop the flow of a liquid but in another place, perhaps of a similar nature, a valve shall accomplish the same purpose. The chief distinction between a cock and a valve is that of its external form.

In Figs. 77, 78 and 79 are three examples of valves that are very generally used on pipes carrying any kind of fluid. The valves are shown in cross-section to display the arrangement of the mechanism.

Fig. 77.-Cross-section of globe valve with detachable valve disc.

Fig. 78. - Cross-section of angle globe valve.

Fig. 79. - Cross-section of gate valve.

Fig. 77 is an example of the common globe-valve. The name was originally intended to define a valve the body of which was in the form of a globe. The hand-wheel H, attached to the screw-stem S, raises the valve A when desired. The valve makes close contact with the seat C, by means of a composition rubber disc B. The disc B may be renewed when worn out as in the case of the radiator valve already described.

Fig. 78 represents an angle globe-valve. In general construction it is quite similar to Figs. 14 and 15, but the valve V in this case is a cone-shaped piece of brass, which makes a seat in a depression provided for it. The valve V and the seat are formed as desired and then ground into contact with emery dust or other abrasive material, to assure a perfectly tight joint. When this valve becomes worn and begins to leak, it may be repaired by regrinding, but such work requires the services of a pipe-fitter. The tendency of modern practice is to use valves with the detachable discs, such as that of Fig. 77, because they are easily repaired.

The valve shown in Fig. 79 is known as a gate-valve. The upper part, including the screw and stem, is the same as the globe style but the valve proper is made in the form of two flat gates A-A. When the valve is closed, as it appears in the drawing, the gates are forced against the seats by the cone-shaped piece B, which acts as a wedge, to tightly close the opening. When the hand-wheel is turned to open the valve, the gates are raised and are taken entirely out of the path of the flowing liquid. Gate-valves are used in places where it is desired to obstruct the flow as little as possible. They are somewhat more expensive than globe-valves but are considered worth the extra expense in service.