“Auto Seat Technology”®
The adjustment screw in the Mercer Valve is a non-rising stem, meaning that when adjusting the set pressure the adjustment screw does not move up or down. When the adjustment screw is turned, it moves the adjustment bushing straight up and down increasing and decreasing the tension in the spring. The adjustment bushing never turns. Because the adjustment bushing never turns, it does not transmit a torque into the disk and seat when adjusting the set pressure. This helps extend the seat life of the valve.
Due to Mercer Valve having a non-rising stem design the adjustment screw never moves up and down. Because the adjustment screw is always in the same place it can be used as a mechanical stop for the disk. This allows the disk to open the same amount each time the valve opens. This gives the valve the same capacity every pop. The mechanical stop is positioned so that the disk is always held up by the flow of the valve until the pressure drops low enough to reclose the valve. The mechanical stop also does not allow the spring to be over compressed, reducing stress on the spring.
FULLY GUIDED SPRING
The spring in the Mercer Valve is guided from top to bottom. With a fully guided spring the spring is only compressed vertically so the spring keeps consistent tension from one pop to the next.
FULLY GUIDED DISK
The disk is aligned on the top through the adjustment screw and at the bottom of the disk by the radius on the disk. When a relief valve begins to vent, the flow of the valve pulls everything toward the outlet. Guiding the disk allows the disk to only move up and down and not to the sides. This keeps the disk from being pulled toward the outlet. With the disk only rising up and down the disk has a consistent opening and reseating. The radius on the bottom of the disk also helps insure that the valve reseats after each pop. If the disk is not centered on the nozzle at reclose, the radius on the bottom of the disk helps to realign the disk. The spring force will push the disk down and the radius will allow the disk to roll back into place.
LOW SPRING RATES
A spring rate is the amount of force the spring exerts for how much it is compressed. Mercer Valve uses low rated springs to help keep stresses out of the spring. The more force that the spring is exerting, the higher the stresses in the spring. When a spring is over stressed the properties of the spring are changed, affecting the set pressure of the valve.
LIP SEAL SEAT
Mercer uses a lip seal soft seat. On reclose the seat flexes, allowing the brute impact of the disk reclosing to be taken by the hard nozzle, while still providing the soft seat seal. Also before the valve reaches set pressure, the pressure is applied underneath the lip seal, pushing the seat against the disk. This gives a tight seal up to the set pressure and extends the seat life.