The combined operation of the two pilots sustains a constant pressure upstream of the valve, and at the same time, reduces the downstream pressure to a preset pressure. Both pilots have spring-loaded diaphragms. One pilot is sensitive to upstream pressure and the other to downstream pressure. The valve opens or closes gradually to maintain both required pressures simultaneously.
Ooval valves are piloted hydraulic valves activated by line pressure. The pilot
valve has a spring-loaded diaphragm that is sensitive to downstream pressure. The pilot's spring is preset to the desired reduced pressure. The pilot valve maintains a constant downstream pressure by gradually opening and closing the Ooval valves at any flow rate.