Maintenance - Fisher 1808 Instruction Manual

Adjustment
WARning
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The allowable spring range is stamped
on the nameplate. if a pressure setting
beyond the indicated range is required,
substitute the appropriate spring. Be
sure to label the valve to indicate the
new pressure range.
Always use a pressure gauge to
monitor pressure when making
adjustments. Remove the closing
cap (key 12, Figure 6) then loosen
the locknut (key 11). To increase the
setting, turn the adjusting screw
(key 10) clockwise. Turn the adjusting
screw counterclockwise to decrease the
setting. Tighten the locknut to maintain
position and install closing cap.
WARning
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To avoid personal injury or equipment
damage, never adjust the pilot control
spring to produce a set pressure higher
than the upper limit of the set pressure
range for that particular spring.
Set pressure is defined as the pressure at which the
pilot starts to discharge. Each unit is factory-set for the
set pressure specified on the order. If no set pressure
is specified, the unit is factory-set at approximately the
midrange of the spring.
Shutdown
Relief installations
Slowly close the upstream shut-off valves. Release
all pressure from the main valve and pilot by opening
a vent valve. When all pressure has been released,
tighten the fitting.
Backpressure installations
Slowly close the upstream shut-off valve while opening
the bypass valve if an isolating bypass is used. Then
close the downstream shut-off valve, and open both
vent valves to release all pressure from the main valve
and pilot.
Types 1808 and 1808A

Maintenance

Parts are subject to normal wear and must be
inspected and replaced as necessary. Frequency of
inspection and maintenance depend upon severity of
service conditions. The main valve body need not be
removed from the line prior to maintenance.
WARning
!
Avoid personal injury or property
damage from sudden release of
pressure or explosion of accumulated
gas. Before starting disassembly,
isolate the relief valve or backpressure
regulator from line pressure, release
trapped pressure from the body and any
isolated piping, and vent any trapped
loading pressure.
Main Valve
This procedure is performed when inspecting,
cleaning, or replacing any main valve parts. key
numbers are referenced in Figures 3 and 4.
if the trim is to be inspected and no
further maintenance is required, it is
unnecessary to remove the pilot from the
upper casing (key 1) or separate the upper
casing from the lower casing (key 2).
Disassembly
1. Remove the two hex nuts (key 18) from the cap
screws (key 17) that hold the lower casing (key 2)
to the body (key 8).
2. Lift the lower casing away from the body.
3. With the lower casing positioned so that the valve
plug (key 6) is accessible, remove the hex nut
(key 14).
4. Remove the O-ring retainer (key 7), the valve
plug (key 6), the O-rings (keys 9, 10, and 11), and
the back-up rings (key 19).
5. Inspect the O-rings and back-up rings, and replace
as necessary. Check all parts for wear.
6. If no further maintenance is required, proceed
to steps 5 through 8 of the Assembly section. If
maintenance inside the casings is required,
proceed with the following steps.
note
5