8
ANDERSON GREENWOOD
TYPE 91 AND 94 PILOT OPERATED SAFETY RELIEF VALVES
INSTALLATION AND MAINTENANCE INSTRUCTIONS
4.0 PILOT SET PRESSURE ADJUSTMENT
4.1 Pilot adjustment
Two adjustments are provided; one for varying
the pressure at which the pilot opens and one
for varying the pressure at which the pilot
closes. The first adjustment controls the “set”
or “popping” pressure, the second the “reseat”
or “blowdown” pressure. To adjust set pressure,
a test set-up similar to that shown in Figure 6
should be used.
4.2 Set pressure
This adjustment is obtained by turning
the pressure adjusting screw, clockwise (in) to
increase set pressure and counter-clock-wise
(out) to decrease set pressure.
4.3 Reseat pressure
This adjustment is obtained by turning
the blowdown adjusting needle screw, clockwise
(in) to increase blowdown, counter-clockwise
(out) to decrease blowdown. A small interaction
between set pressure and reseat pressure
adjustments will occur, therefore it may be
necessary to readjust the set pressure after
setting reseat pressure.
4.5 ADJUSTMENT TOLERANCES
Non-marine service
Pilot action
[1]
Set pressure
Set pressure
tolerance
Minimum crack
pressure as % of set
Supply pressure as % of set for
dome pressure recovery
[2]
English (psig)
Metric (kpag)
Snap
7” WC to 1.0 psig
1.74 kpag to 6.89 kpag
+/- 3%
90
90 +/- 1
Above 1 psig to 15 psig
Above 6.89 kpag to 103 kpag
+/- 3%
92½
92½ +/- ½
Above 15 psig to 50 psig
Above 103 kpag to 345 kpag
+/- 3%
92½
92½ +/- ½
-7” WC to -1.0 psig
-1.74 kpag to -6.89 kpag
+/- 3%
90
90 + 1
Above -1.0 psig to -14.7 psig
Above -6.89 kpag to -101 kpag
+/- 3%
92½
90½ + ½
Modulating
7” WC to 1.0 psig
1.74 kpag to 6.89 kpag
+/- 3%
90
100 + 0/- 2
Above 1.0 psig to 15 psig
Above 6.89 kpag to 103 kpag
+/- 3%
92½
100 + 0/- 2
Above 15 psig to 50 psig
Above 103 kpag to 345 kpag
+/- 3%
92½
100 + 0/- 2
-7”WC to -1.0 psig
-1.74 kpag to -6.89 kpag
+/- 3%
90
100 + 0/- 2
Above -1.0 psig to -14.7 psig
Above -6.89kpag to -101 kpag
+/- 3%
92½
100 + 0/- 2
Marine service
Pilot action
[1]
Set pressure
Set pressure
tolerance
Minimum crack
pressure as % of set
Supply pressure as % of set for
dome pressure recovery
[3]
English (psig)
Metric (kpag)
Snap
4 psig to 21 psig
27.6 kpag to 145 kpag
+/- 10%
75
92 +/- 2
Above 21 psig to 42 psig
Above 145 kpag to 290 kpag
+/- 6%
75
92 +/- 2
Above 42 psig to 150 psig
Above 290 kpag to 1034 kpag
+/- 3%
75
92 +/- 2
NOTES
1.
Snap action
Dome pressure decreases rapidly with a “snap” to 15% + 10% of set pressure at set pressure. Pilot seat should be bubble tight at dome pressure recovery.
Modulating action
Dome pressure decreases slowly to 30% + 5% of set pressure and recovers to 60% + 10% of set pressure at set pressure.
2. Pilot seat should be bubble tight at dome pressure recovery for “snap” pilot action and at 90% of set pressure for “modulating” pilot action non-marine.
3. For marine valves, the pilot seat should be bubble tight at 75% of set pressure.
NOTE
If the blowdown adjusting screw has been moved
or turned to either extreme, positioning it midway
will aid in obtaining the correct blowdown.
There are approximately 7 to 8 turns to obtain full
travel of the adjustment. Midway from either end
should produce a blowdown for “snap action”.
For “modulating pilot action”, back the adjustment
screw out (counter- clockwise) to obtain
the adjustment limits given in paragraph 4.5.
4.4 Range of adjustment
All Pilots can be adjusted ±10% beyond
the nameplate setting.
