Main Valve Maintenance - Pentair Anderson Greenwood 93 Series Installation And Maintenance Instructions Manual

Anderson Greenwood SerieS 93 PoSitive PreSSure PoSrv
InstallatIon and MaIntenance InstructIons
external
blowdown
adjustment
outlet
Main valve
(typical)
FiGure 1
1.2 installation
Both inlet and outlet may be standard ANSi or
DiN flange connections and are to be installed
in accordance with accepted piping practices.
the installed position of the safety valve should
be in the upright position as shown in Figure 1.
When remote pressure pick-up is used the pilot
supply tube is connected to a remote location
rather than to the inlet neck of the valve. if a
block valve is used in the remote pilot supply
line, be sure it is opened before pressurizing
the system.
note: remote pressure pick-up piping must
have the equivalent flow area of ½" tubing for
lengths up to 20 feet. For lengths greater than
20 feet, larger tubing or pipe should be used.
1.3 start-up
there must be pressure at the valve inlet
to establish a differential in force across
the diaphragm and "load" it in the closed
position. Pressure must pass through the pilot
supply tube and pilot and exert force on the
diaphragm. on normal start-up the valve loads
itself without incident as pressure increases.
Block valves are often used under safety valves
in order to isolate them when maintenance
is required. When putting the safety valve in
service be sure the block valve is fully opened.
if the block valve is opened after system start-
up, the safety valve may briefly vent to the
atmosphere before the dome gets pressurized.
it will then close.
2 MAin VAlVe MAintenAnce (refer to
fiGures 2 And 2A)
2.1 Valve configuration
two different valve internals are used in the
main valve, depending on set pressure. the
sponge seat is used for the set pressures
shown below. the o-ring seat with guide is
used for all pressures above these values. For
some applications, a guide may be used in
place of item 11 with a sponge seat.
Pilot valve
Supply tube
Nameplate
inlet
set pressures where sponGe seAt
is used
Valve size
2 x 3
3 x 4
4 x 6
6 x 8
8 x10
10 x12
12 x16
2.2 disassembly
Disconnect the supply tube from the pilot,
remove the cap bolts, lift the cap from the valve
body and lift the diaphragm, seat and guide
(where used) from the valve. remove the seat
bolt(s) to separate the diaphragm from the
seat, guide, and retainer plates.
2.3 repair
inspect the nozzle seating area for nicks or
scratches. if they cannot be removed with
crocus cloth or fine sandpaper, the nozzle must
be remachined. on steel valves the nozzle
may be removed from the body. Machining of
the nozzles should be limited to .06" material
removal.
2.4 Assembly
reassemble the diaphragm, seat guide,
and pilot supply tube in the reverse order of
disassembly. Apply a light film of lubricant to
all threaded parts. Care should be taken to
adequately tighten the seat bolt(s) on those
valves with guides to prevent the diaphragm
from pulling away from the bolt under
pressure.
on valves with sponge seats (no guide), the
seat bolt need not be tightened as much since
these valves are used at lower pressures and
excessive tightening will distort the seat.
Carefully insert the guide (where used) squarely
into the nozzle and lower the diaphragm
assembly into place. Align the holes on the
diaphragm o.D. with those on the body.
the guide spring, item 3, is used to create
frictional drag to prevent valve chatter caused
by excessive inlet piping pressure losses. the
tension of these springs is correct when the
diaphragm/guide assembly slowly free falls to
the closed position. if the assembly will not do
this, adjust the spring tension by bending the
tail or lower half of the spring.
Refer to paragraph 8 for Soft goods repair kits
set pressure (psig)
Below 2.5 psig
Below 1.5 psig
Below 1.0 psig
Below 1.0 psig
Below 1.0 psig
Below 1.0 psig
Below 1.0 psig
2