9
Repair Instructions P420 / P420-0011 / P420-0021 / P422 / P423 and P425
Note: Always take time to lubricate all metal and nonmetal parts with a light film of oil before reassembly. This step
will ensure proper fit, at the same time protecting the pump nonmetal parts (i.e., the elastomers) from cutting and
scoring.
1) With a socket wrench,
remove the three dis-
charge valve plugs and
three inlet valve plugs
(32). Inspect the o-ring
(33) for wear and replace
if damaged.
2) Using needle nose pli-
ers, remove the inlet and
discharge valve assem-
blies (27A). Note: It
may become neccesary
to remove the valve seat
(27) from the valve casing
using a slidehammer.
3) By inserting a small screw
driver between the valve
seat (27) and the valve
spring retainer (30), the
valve assembly can be
separated.
4) Remove the o-ring (31).
Inspect all parts for wear and
replace as necessary. Apply
one drop of loctite 243 to the
valve plugs (32) and tighten
to 107 ft.-lbs. (145 NM).
5) Use a 8mm allen wrench
to remove the 8 socket
head cap screws (34).
Carefully slide the valve
casing (26) out over the
plungers.
6) Remove seal case (20)
and weep return rings
(25) from the valve
casing.
7) Remove the pressure
rings (24) and v-sleeves
(23 - Note: P422 & P423
pumps have a spacer
ring) from the valve cas-
ing (26).
8) Remove the weep grooved
seal (23 or 23B) together
with pressure ring (24)
P420 and P425 only) out
of the seal case (20).
Check O-rings (21).
IMPORTANT!
The grooved
seal (23) on the high-
pressure side is to be fitted
carefully into the valve cas-
ing (26) using a screwdriver.
Under no circumstances
must the seal surface in the
valve casing or the seal lip
be damaged.
