A back pressure valve is a kind of relief valve to obtain a constant level of pressure in the first stage of valve operation. This type of valve makes it easier and speedier for the user to control pressure in the tank with a large buffer, purge a given quantity of mixed gas or to carry out such other operations which are rather hard to do with a secondstage control valve commonly in use.
The pressure regulating valve controls the pressure applied to the flow to keep it constant or reduce the pressure during flow control. Pressure regulating valve are classified into reducing valves and back-pressure valves. Reducing valves make the outlet-side pressure constant when the pressure on the inlet side changes, and are used at the first stage of systems in general. Meanwhile, back-pressure valves are a kind of constant-volume relief valve that remove gas while keeping the primary-side pressure constant.