Technical Specifications

5
A back pressure regulator or relief regulator controls
upstream pressure instead of downstream pressure.
The control action in the pilot is the reverse of a pilot
for a pressure reducing regulator (increasing pressure
in the sense chamber opens the pilot regulator). At no
flow, when the inlet pressure is less than the set point
of the pilot regulator, the pilot is closed and full inlet
pressure loads the spring case through the pilot loading
connection. In this condition, the diaphragm is closed
tightly against the throttle plate. The pressure differential
across the outlet half of the diaphragm adds to the
spring force in closing the Flowgrid regulator (Refer to
figure 6).
As inlet pressure increases above the set point of the
pilot regulator, it will open and start bleeding pressure
out of the spring case faster than it can enter through
the restrictor. Reducing the pressure above the dia-
phragm allows inlet pressure to progressively
Hydrostatic Testing
All Flowgrid regulators are hydrostatically tested at the
factory prior to shipment according to ISA-S75.19-1989
and MSS-SP-61 standards. If it is necessary to retest the
regulator, follow one of the procedures listed below to
prevent damage to the diaphragm.
Option 1
1. Disconnect and remove all control line(s) and the
pilot from the Flowgrid regulator.
2. Loosen main spring case nuts in a crisscross pattern.
The main spring will lift the spring case as the nuts
are removed.
3. Remove main spring and diaphragm from regulator.
For all 1”, 2”, 4”, 6” (and 10”-V6) Flowgrid Regulators
4. Replace diaphragm with a used
diaphragm that has the thick padded
area cut out leaving the outer sealing
surface (see below).
This area removed
For 3” and 4” x 3” Flowgrid Regulators
4. Remove diaphragm but leave diaphragm O-ring in
place. Make sure O-ring is properly seated.
5. Reassemble spring case on Flowgrid regulator.
6. Tighten main bolts in increments using a crisscross
pattern. Torque bolting as indicated on regulator
nameplate (or refer to Table 6 Page 14).
7. Plug spring case loading port, pilot inlet and outlet
taps on Flowgrid regulator.
8. Refer to Table 4 for the maximum hydrostatic test
pressure of each Flowgrid regulator.
9. After hydrostatic test is completed follow the
Dissassembly, Cleaning, and Assembly procedures in
the Maitnenace section of this manual
Option 2
1. Disconnect and remove all control line(s) and pilot from
the Flowgrid regulator.
2. Pipe regulator with the inlet, outlet, and loading
connections all common so that pressure is
equalized in the entire regulator during the
hydrostatic test (See Figure 8).
3. Refer to Table 4 for Maximum hydrostatic test
pressure of each Flowgrid regulator.
4. After hydrostatic test is completed follow the
Disassembly, Cleaning, and Assembly procedures
in the Maintenance section of this manual.
End Connection Max. Hydrostatic Test Pressure
Screwed & Socket Weld 2225 psi (153.41 bar)
150# Flange & Flangeless 450 psi (31.02 bar)
300# Flange & Flangeless 1125 psi (77.56 bar)
600# Flange & Flangeless 2225 pis (153.4 bar)
Flowgrid 250
1
375 psi (25.86 bar)
1
The Flowgrid 250 is a ductile iron construction.
Table 4 - Maximum Hydrostatic Test Pressures
Figure 8 - Flowgrid Tee Connections
A. Inlet connection on regulator body joined to “Tee”.
B. “Tee” connected to loading connection on spring case.
C. Outlet of “Tee” connected to outlet connection on
regulator
lift the throttling element off the throttle plate opening
the regulator and satisfying the demand for flow in the
upstream system (Refer to Figure 7).
When upstream pressure decreases, causing the pilot
regulator to close, pilot supply pressure continues to
pass through the restrictor until the control pressure
equals the inlet pressure. The spring force, plus the pres-
sure differential across the outlet half of the throttling
element closes the diaphragm against the throttle plate,
shutting off the flow (Refer to Figure 6).
Adjustment of the restrictor affects the response rate,
stability, and sensitivity of the regulator. Smaller restric-
tor openings result in higher gain (sensitivity) and slower
closing speeds. Larger openings result in lower gain
(greater proportional band), greater stability and faster
closing speeds.