All valves are divided into adjusting, protective, safety, reverse and outlet. All the names of the valves reflect their purpose. So, for example, the adjusting valve is a shutter that, when moving downwards, makes a locking. In this case, the shutter of such a valve is an element resembling a plate. Either a spring or a special load is used to cut automation in such valves. Finding valves are designed to limit the reverse flow. Cut valves are opened using pressure, which is created by a directed stream, and closed by the same stream only when it goes in the opposite direction. This type of valves is a special shutter, which rotates on a horizontal plane, being above the center of the saddle. Safety valves differ in terms of their work. At leisure it will not be superfluous to find out what can be done on your own on the Internet.
There are safety valves of direct and not direct action. The former are triggered due to the effect of the working flow, and the latter work using an additional drive. But this is not all the separation of safety valves, because the valves of not direct action are additionally divided into pulsed and forced.