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Displacement Pump Service
Disassembly
1. Disconnect the displacement pump from the air
motor (1), as explained on page 15.
2. Unscrew the packing retainer (106) from the pump
cylinder (101). Pull the entire pump assembly out
of the bottom of the cylinder. See Fig. 9.
3. Drive the pin (112) out of the connecting rod (102)
and piston (104). Unscrew the piston from the rod.
Slide the seal (103) off the piston.
4. Drive the pin (112) out of the piston (104) and
priming piston rod (107). Unscrew the rod.
5. Slide the intake seal (105) off the rod (107). This
may be difficult because there is friction between
the seal and rod.
6. Slide the packing retainer (106) off the rod (107).
Remove the o-ring (111) from the packing retainer.
7. Examine the o-ring (111) and priming piston (108)
for scoring or damage. It is normal for the piston to
show some movement on the rod. If either parts
needs replacement, go to step 8.
8. If the rod (107) or the priming piston (108) needs
to be replaced, insert a punch in the pin hole at the
top of the rod to hold it steady. Unscrew the nut
(109), and remove the priming piston. If 107 or
108 do not need to be replaced, leave
assembled.
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Reassembly
1. If the priming piston (108) was removed from the
priming piston rod (107), reinstall it on the bottom
threads of the rod (the end without a pin hole) and
secure with the nut (109). Torque to 35 to 45 in-lb
(4.0 to 5.1 N-m). Lubricate the rod. See Fig. 9.
2. Lubricate the o-ring (111*) and install it on the
packing retainer (106). Slide the retainer onto the
rod (107), with the o-ring at the top. Lubricate the
intake seal (105*) and slide it onto the rod, with the
flat side facing the packing retainer. There should
be friction between the seal and the rod. If there is
very little or no friction, replace the rod or the seal.
It is not necessary to slide the seal all the way
down to the retainer.
3. Screw the piston (104) onto the rod (107) until the
pin holes align. Install the pin (112*). Be sure that
the pin is flush or below the surface of the piston
on both sides.
4. Lubricate the seal (103*) and install it on the piston
(104), with the large bevel facing the piston.
5. Screw the connecting rod (102) onto the piston
(104) until the pin holes align. Install the pin (112*).
Be sure that the pin is flush or below the surface of
the connecting rod on both sides.
6. Lubricate the inside of the cylinder (101). Slide the
rod assembly into the bottom of the cylinder. There
may be a lot of friction, but do not use a hammer
or rubber mallet to drive the assembly, to avoid
damaging the parts.
7. Screw the packing retainer (106) into the cylinder
(101). Using a socket wrench or crow's foot
wrench, torque to 15 to 20 ft-lb (20 to 27 N-m).
8. Continue to push the rod assembly up as far as
possible. Reconnect the displacement pump to the
air motor (1) as explained on page 15.
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