Valve

Valves are the components in fluid flow or pressure system which regulate either the flow or the pressure of fluid.This duty may involve stopping and starting flow,controlling flow rate,preventing back flow,controlling pressure,or relieving pressure.
These duties are performed by adjusting the position of the closure member in the valve.this may be done either manually or automatically;manual operation includes also operation of the valve by mean of manually controled power operator.The valves discussed here are manually operated valves for stoping and starting flow,controlling flow rate and diverting flow;and automatically operated valves for preventing back flow and relievinf pressure.The manually oprated valves are refer to as manual valves,while valves for prevention of back flow and the relief of pressure are refered to as check valves and pressure relief valves,respectively.
Rubture discs are non-reclosing pressure reliving devices which full fill a duty similar to pressure reducing valves.