Pilot Set And Reseating Pressure Adjustment - Emerson ANDERSON GREENWOOD 727 Installation And Maintenance Instructions Manual

ANDERSON GREENWOOD TYPE 727 DUAL PILOT MANIFOLD
INSTALLATION AND MAINTENANCE INSTRUCTIONS
7 PILOT SET AND RESEATING PRESSURE
ADJUSTMENT
Two pilot adjustments are provided; one for
adjusting the pressure at which the pilot opens
(set pressure) and one for varying the pressure
at which the pilot closes (reseating pressure).
Definitions
Definitions of test pressures: (unless specified
otherwise on the procurement document).
1. Set pressure - the pressure at which
the pilot reduces the main valve dome to
40% or less of supply. Also referred to as
nameplate set.
2. Cold differential test pressure - the
pressure at ambient temperature which
the pilot is adjusted to open on the test
stand and which includes corrections
for certain service conditions such as
high temperature. This pressure is also
included on the main valve nameplate.
3. Cracking pressure
Steam - The point at which with increasing
pressure the pilot exhibits 60
bubbles per minute air leakage or
first visible steam leakage.
Air - The point at which with increasing
pressure the pilot exhibits the first
bubble of leakage.
4. Reseating pressure - the pressure
at which the pilot valve closes.
5. Dome pressure - the pressure which is
present, at any given time, in the main
valve 'dome' area.
6. Blowdown - the difference between the
set pressure and the reseat pressure,
expressed as a percent of set pressure,
or in psig.
Test procedures
The ASME Section 8 pressure vessel
code requires the pilot on pilot operated
valves for steam service be set using
steam except those pilots which have set
pressure beyond the capability of the test
facility. These pilots may be set using air.
Current Anderson Greenwood procedures
require all steam valves to be set on air and
verified on steam as described in the following
sections of this report. All pilots for vapor
service are required only to be set on air using
the pilot test stand.
A pilot's air set pressure is defined as the cold
differential test pressure and is indicated as
such on the main valve nameplate.
1. Test set up - install the pilot valve on the
test drum similar to that shown in Figure 9.
The 'dome' connection is a blind connection
with a pressure gauge to indicate the dome
pressure reduction achieved while the pilot
actuates at set pressure. The test drum
must be equipped with cartridge pilot field
test fixture assembly Anderson Greenwood
Part no. 06.3036.002.
2. Set pressure adjustment (refer to
Figure 6) - to adjust pilot set pressure
remove pilot cap (512), loosen locknut
(510) and rotate spring adjusting screw
(511) clockwise to raise set pressure or
counter-clockwise to lower set pressure,
as required.
Note: to ensure an accurate pilot action,
tighten locknut and replace pilot cap after
each adjustment is made.
3. Reseat adjustment - to adjust the reseat
pressure, depressurize the pilot test fixture
and remove pilot from the fixture. Loosen
the blowdown locknut, rotate blowdown
screw clockwise to shorten blowdown or
counter-clockwise to increase blowdown
as required and tighten locknut.
4. Performance check - reinstall pilot on
pilot test fixture and cycle the pilot valve
a minimum of three times after the above
adjustments to verify it is relieving and
reseating at consistent pressures. Increase
and decrease the pressure slowly during
these cycles to obtain an accurate reading
of the test pressures and to expose any
erratic pilot performance.
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