Instruction Manual

Types 1808 and 1808A
5
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





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








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




Set pressure is dened as the pressure at which the
pilot starts to discharge. Each unit is factory-set for the
set pressure specied on the order. If no set pressure
is specied, the unit is factory-set at approximately the
midrange of the spring.


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 tting.

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.

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.
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









This procedure is performed when inspecting,
cleaning, or replacing any main valve parts. Key
numbers are referenced in Figures 3 and 4.






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.