The BP-3 Series is designed for either liquid or gas service and primarily for instrumentation systems. Similar in design to pressure reducing regulators, which regulate outlet pressures, back pressure regulators control the inlet pressure. The main features of this valve, including its precise throttling action, make it ideal for this type of application. In most systems over-pressures are often released by pressure relief valves, which are simply on or off with no throttling control. In contrast to the on or off action of a relief valve, a back pressure regulator provides throttling action and substantially improves system regulation.