A pressure controls valve is an essential safety valve, limiting the pressure within a system to prevent process upsets, equipment and instrument failure, and fire. These valves limit the pressure in a system so that it doesn't cause damage to people or property. The pressure controls valve can be manually operated or electrically operated.

These valves can be adjusted for maximum pressure or minimum pressure. A spring-loaded valve can be adjusted by turning the adjusting screw, which varies the spring pressure against the diaphragm. When the pressure in the system goes above the set level, the valve will open. Then, when the pressure drops below the set pressure, the valve closes.

A Pressure Controls Valve is a mechanical valve mounted on a line at a zone boundary. It has a nominal opening pressure of 1.5 to 2.0 in wg, and is suited for both pressure and flow applications. It is also available in two-stage designs and with different pressure ranges.

Pressure balance valves have a primary port that is connected to the cylinder rod end and a secondary port that is connected to a directional control valve. The valve is set to slightly higher pressure than the load to counterbalance. When the load increases, the pressurized fluid flows to the cylinder cap end, extending the rod. In turn, the increased pressure shifts the main spool within the valve.