Bulletin 71.4:63EG-98HM
3
CO MP
Principle of Operation
As long as inlet pressure remains below set pressure, the
pilot control spring keeps the pilot valve plug closed. This
pressure provides the loading pressure that helps the main
valve spring keep the main valve plug tightly shut off.
An inlet pressure rise above the set pressure overcomes the
pilot control spring and opens the pilot valve plug. Loading
pressure bleeds out the pilot exhaust faster than it can be
replaced through the restriction. This permits inlet pressure
to unbalance the main valve plug and open the main valve.
As inlet pressure drops back to set pressure, the pilot control
spring closes the pilot valve plug. Loading pressure again
builds up to close the main valve plug.
Example Sizing Problem:
To have a pump recirculation of oil and hold backpressure.
The pump capacity is 180 GPM / 681 l/min, the oil has a
specic gravity (G) of 1.00 and the temperature is ambient.
TYPE MR98H
TYPE 63EG
FIXED RESTRICTION
CONTROL LINE
(MUST BE AT LEAST
3/8 IN. / 9.52 mm TUBING)
PILOT CONTROL
SPRING
PILOT VALVE PLUG
MAIN VALVE SPRING
MAIN VALVE PLUG
PILOT EXHAUST
(PIPE DOWNSTREAM
IF MINIMUM DIFFERENTIAL
IS MET)
A6926_2
Note: On an actual Type 63EG-98HM, the pilot spring case points downstream.
Figure 2. Operational Schematic
INLET PRESSURE
OUTLET PRESSURE
LOADING PRESSURE
ATMOSPHERIC PRESSURE
P
1
(Inlet Pressure) = 25 psig / 1.7 bar
P
2
(Outlet Pressure) = 15 psig / 1.0 bar
Q (Flow) = 180 GPM / 681 l/min
Calculated C
v
= 57
The differential pressure (P
1
– P
2
) is 10 psig / 0.69 bar. From
Table 4, it is determined that NPS 2 / DN 50 main valve has
the needed capacity. The pilot exhaust is piped downstream
of the valve. With the pipeline size equaling the valve body
size and using a linear cage, the C
v
is equal to 63.3 as
shown in Table 4. Since the differential pressure is less than
40 psig / 2.8 bar, Table 5 veries that the yellow main valve
spring can be used. To maintain the best accuracy, always
use the lightest spring rate available. The pressure build-
up to a wide-open state is 7 psi / 0.48 bar over setpoint.
The setpoint on a relief valve or backpressure regulator is
dened as when the pilot begins to bubble or open. Since
the setpoint is 25 psig / 1.7 bar and the build-up required to
fully open the regulator is 7 psi / 0.48 bar, the total upstream
pressure would be at 32 psig / 2.2 bar. The differential
pressure between P
1
– P
2
, 32 – 15 psig / 2.2 – 1.0 bar, is
17 psi / 1.2 bar.
INLET PRESSURE
OUTLET PRESSURE
ATMOSPHERIC PRESSURE
TANK PRESSURE
VACUUM PRESSURE
PRE-EXPANSION PRESSURE
INTERMEDIATE BLEED PRESSURE
PILOT SUPPLY PRESSURE
INTERMEDIATE PRESSURE
LOADING PRESSURE
PUMP PRESSURE
BYPASS PRESSURE
BACK PRESSURE
INLET PRESSURE
OUTLET PRESSURE
ATMOSPHERIC PRESSURE
VACUUM PRESSURE
PRE-EXPANSION PRESSURE
INTERMEDIATE BLEED PRESSURE
PILOT SUPPLY PRESSURE
INTERMEDIATE PRESSURE
PILOT SUPPLY PRESSURE
VACUUM PRESSURE
TANK PRESSURE
VAPOR PRESSURE
LOADING PRESSURE
BYPASS PRESSURE
BACK PRESSURE
PUMP PRESSURE
BOOST PRESSURE
EXHAUST
PILOT LOADING PRESSURE
VENT HEADER PRESSURE
INLET BLEED PRESSURE
RELIEF PRESSURE
RELIEF PRESSURE
BOOST PRESSURE
MONITOR MOVING PRESSURE
STABILIZED PRESSURE
INLET BLEED PRESSURE
INITIAL STEP-DOWN PRESSURE
OUTLET PRESSURE (WHEN LOADING PRESSURE IS EQUAL TO OR GREATER THAN SETPOINT)
(1 pages)
(16 pages)
(12 pages)
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