Data Sheet

Bulletin 71.4:MR98
8
Principle of Operation
Relief or backpressure valves respond to changes in
upstream pressure. Pressure changes register under
the diaphragm (see Figure 2) through a registration
hole in the valve body or through an external control
line. When the pressure increases beyond the spring
setting, the diaphragm pressure overcomes the spring
compression. This causes the valve plug to move
away from the orice. The ow path through the
SPRING
SPRING
METAL DIAPHRAGMS
METAL DIAPHRAGM
GASKET
GASKET
FOR TYPE MR98H WITH TWO METAL DIAPHRAGMS
(ALSO TYPICAL OF TYPES MR98HH AND MR98L EXCEPT FOR
psi / 0.1 TO 0.48 bar RANGE)
psi / 0.14 TO 0.48 bar RANGE)
WITH ONE METAL DIAPHRAGM
Figure 2. MR98 Series Operational Schematics
CONTROL SPRING
DIAPHRAGM
ORIFICE
VALVE PLUG
VENT
ADJUSTING SCREW
TYPE T208 WITH INTERNAL REGISTRATION
INLET PRESSURE
OUTLET PRESSURE
ATMOSPHERIC PRESSURE
TYPE T208M WITH EXTERNAL REGISTRATION
INLET PRESSURE
OUTLET PRESSURE
ATMOSPHERIC PRESSURE
ERSA02737
ERSA02738
CONTROL LINE TAP
TYPE MR98H WITH INTERNAL
PRESSURE REGISTRATION
BACK VIEW OF
1/2 IN. / DN 15 TYPE MR98H
WITH EXTERNAL
PRESSURE REGISTRATION
SIDE AND INTERNAL VIEW OF
3/4 TO 2 IN. / DN 20 TO 50
TYPE MR98H WITH EXTERNAL
PRESSURE REGISTRATION
(ALSO TYPICAL OF TYPE MR98L,
1/2 TO 2 IN. / DN 15 TO 50 BODIES)
valve is open and excess pressure is vented. When
upstream pressure drops below setpoint, the valve
resumes its closed position.
Differential relief valves are used to maintain a
differential pressure between the controlled pressure
and loading pressure of a system. The spring setting
determines the differential.