The relief valve in the system up security role. When the system pressure, the relief valve open more than rating, will be part of the system gas/fluid is vented to atmosphere/pipeline, the system pressure outside not more than the allowable value to ensure system not by the pressure is too high and the accident. The relief valve and relief valve says, or relief valves, but it and relief valve and have some difference. Here are several typical structure form of the relief valve. Figure a for piston relief valve, the valve core is a flat. Air pressure in the pistons on A role, when pressure is more than the spring force determined by the greater A is open, the top part of compressed air, from the mouth is vented to atmosphere; When air pressure is lower than secure value, spring driving the piston moves down, close the valve mouth. This valve seal face to clean