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CROSBY STYLE JQ 4 IN. PRESSURE RELIEF VALVE
INSTALLATION AND MAINTENANCE INSTRUCTIONS
As the lapping nears completion, only the
compound left in the pores of the block should
be present. This should give a very smooth finish.
If scratches appear, the cause is probably dirty
lapping compound. These scratches should
be removed by using compound free from
foreign material. Disc inserts should be lapped in
the same way as nozzles. The disc insert must be
removed from the holder before lapping. Before the
disc insert is placed back in the holder all foreign
material should be removed from both parts. The
insert must be free when in the holder. If the disc
insert is damaged too badly to be reconditioned by
lapping, it should be replaced. Remachining the
insert will change critical dimensions, affect the
action of the valve and is not recommended.
8.4.4 Lapping Blocks
Lapping blocks are made of a special grade of
annealed cast iron. There is a block for each
orifice size. Each block has two perfectly flat
working sides and it is essential that they
retain this high degree of flatness to produce
a truly flat seating surface on either the disc
insert or the nozzle. Before a lapping block
is used, it should be checked for flatness and
reconditioned after use on a lapping plate. The
block should be lapped in a figure eight motion,
applying uniform pressure while rotating the
lapping block against the plate as shown in
Figure 2.
8.4.5 Lapping Compounds
Experience has proven that medium coarse,
medium fine and polish lapping compounds will
condition any damaged pressure relief valve
seat properly except where the damage requires
remachining. The following lapping compounds,
or their commercial equivalents are suggested
in Table 8.4.5.
TABLE 8.4.5 LAPPING COMPOUNDS
Abrasive
Silicon Carbide
Silicon Carbide
Silicon Carbide
Hard Alumina or Aluminum Oxide
White Aluminum Oxide
8.5 Reassembly of Safety Valve Proper
CAUTION
Failure to follow these instructions may result in
improper function of the valve.
Always wear proper PPE.
During reassembly, lubricate all threads, ball
joints and guiding surfaces (6.2.3).
8.5.1 Reassembly of Nozzle (13) and Base (17)
To assemble the Nozzle (13) and the Base (17),
use a new Nozzle Gasket (14) that is lightly
lubricated on one side. Screw the Nozzle (13)
into the Base (17) and tighten. The Adjusting
Ring (11) should then be installed on the
Nozzle (13); however, do not install the Lock
Pin (12) at this time but turn the ring to its
lowest position.
Be careful not to damage the seating surface
of this assembly in any way or the valve will not
pass final pressure test.
8.5.2 Install Disc Guide (7)
Install the Disc Guide (7) by screwing it onto the
Base (17). Next, install the Lock Screws (18) by
using a hex wrench.
8.5.3 Install Disc (10A), Spring (5), etc.
Hold the Disc (10A) and carefully lower it into
position. Next, place the Spring (5), top Spring
Washer (9), Bottom Spring Washer (19), and the
Spindle Assembly (6) in position. Be sure to use
the proper spring (6.1.2).
8.5.4 Install Adjusting Bolt (3)
Screw the Adjusting Bolt (3) into the Disc
Guide (7). After installing, the Lock Nut (4) should
be tight against the Disc Guide (7).
8.5.5 Set Adjusting Ring (11)
Raise the Adjusting Ring (11) by turning it with a
rod or screwdriver until it touches the Disc (10A).
Lower the Adjusting Ring (11) one notch for
testing by turning with a rod or screwdriver.
Twist a piece of 22-gauge copper wire around
the groove in the Lock Pin. Holding the Lock
Pin (12) with the wire, lower it into position and
tighten with a screwdriver. Then, remove the
wire. Alternatively, an expandable screwdriver
can be used to install the Lock Pin (12).
Grit Size
Average Micron Size
320
400
600
900
1200
FIGURE 2
Motion shown by
dotted lines
Bottom rough
surface do not use
Description
31
Medium Coarse
22
Medium
16
Fine
9
Polish
5
Polish
Top lapping surface
Lapping block to be
squared up
LAPPING BLOCK RESURFACING PLATE
LAPPING BLOCK
U.S. Products Category Number
No. 2F Crystolon
No. 3F Crystolon
No. A-600 Crystolon
No. 38-900-A
No. 38-1200-A
8
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