Cla-Val Models 58-01 and 658-01 valves perform two separate functions. They maintain constant backpressure by discharging excess pressure downstream and when the solenoid is activated, close drip-tight.

When the inlet pressure is greater than the control setting, the valve opens. When the inlet pressure is equal to the control setting, the pilot modulates the valve, maintaining the preselected backpressure. When the inlet pressure is less than the control setting, the pilot system closes the valve drip tight.