The pressure relief valve is a type of valve used to control or limit the pressure in a system or vessel. Exhaust over-pressurization to protect downstream equipment or control the upstream pressure of gas or liquid. It maintains a constant downstream pressure, regardless of fluctuating demand and sustains the upstream pressure to a pre-determined minimum. As a quality pressue relief valve manufacturer, we provide pressure reducing and sustaining valve for sale. They automatically perform two independent functions. The pressure reducing pilot responds to slight variations in downstream pressure and immediately repositions the main valve to maintain the desired downstream pressure. The pressure sustaining pilot is normally held open by the upstream pressure and close when the pressure drop to the set point. We are pressure relief valve supplier for over 18 yeras, the pressure control relief valve usually used in lower elevation pipeline to guarantee prior use of higher elevation area.