Foxboro B0123HE

The range spring, which has been compressed by the adjustment knob and screw, causes the

pintle valve to move downward, allowing air to flow. The pressure builds up against the

diaphragm until the pintle valve throttles. This is the set pressure which is closely maintained in

the following manner: A drop in the regulated line pressure will cause a decrease in the pressure

against the bottom of the diaphragm. The range spring forces the diaphragm down against the

reduced pressure causing the pintle valve to open, admitting more supply air, until the pressure

below the diaphragm balances the spring force. Diaphragm upward motion causes the exhaust

valve in the diaphragm to open. The excess pressure rises into the spring cavity through the

exhaust valve and vents to atmosphere via the exhaust vent.

To install normally replaced parts, the following procedures should be followed.

! CAUTION

Before removing the four cover screws, turn pressure adjusting screw (knob)

counterclockwise on the range spring.