O'Brien PRO 301, Owner'S Manual

17

308–030

DISPLACEMENT PUMP

Reassembly Procedure
1. Stack the backup washer (219*), U–cup seal

(205*) 

lips down, and female gland (220*), al-

ternate the polyethylene and leather v–pack-
ings (217*, 218*) 

lips up, and stack the male

gland (213*) onto the piston valve (224). See
Fig 14.

2. Tighten the packing retaining nut (214) onto

the piston valve (224) and torque to 3–4 in–lb
(0.34 – 0.35 N.m). See Fig 12.

NOTE: NOTE THE ALIGNMENT of the piston

(224) to the nut (214). Maintain this align-
ment throughout Steps 2, 3 and 4.

NOTE AND MAINTAIN
THIS ALIGNMENT
THROUGHOUT STEPS
3,4, AND 5

Fig 12

TORQUE NUT TO

3–4 IN-LB (0.34–0.35

N.M)

APPLY ONE DROP
OF SEALANT TO
THESE THREADS

203*

224

214

3. Apply 

1 drop only of sealant, supplied with the

repair kit, to the piston valve threads. Place
the small ball (203*) on the valve. See Fig 12.
Hand tighten the valve into the rod (223) just
until the nut contacts the rod. Place the flats of
the displacement rod in a vise.

Fig 13

214

TORQUE NUT

ONTO ROD TO 19

FT-LB

(25 N.M)

223

4. Torque the nut (214) onto the rod (223) to 

19 ft–lb (25 N.m). Use two wrenches to main-
tain the alignment as mentioned in the NOTE.
See Fig 13.

5. Stack the male gland (211*), alternate the

polyethylene and leather v–packings (218*,
209*) 

lips down and stack the female gland

(212*) one at a time into the top of the cylin-
der. See Fig 14.

6. Loosely install the packing nut (221) and plug

(201).

7. Insert the oiled piston rod (223) into the bot-

tom of the cylinder.

8. Assemble the intake valve. Use a new gasket

(206*). Screw the valve into the cylinder and
tighten to 80 ft–lb (107 N.m). See Fig 14.

9. Screw down the cylinder locknut (31) until it is

finger tight at the bottom of the external cylin-
der threads. See Fig 14.

10. Install the displacement pump on the sprayer.

Lips must face up

*208

216

APPLY 1 DROP
OF ADHESIVE (in
repair kit) TO
THESE THREADS

Fig 14

201

223

*204

215

222

*206

*207

Lips must 
face up

217*

Lips must 
face down

218*

Lips must

face down

*209

224

Lips of seal 

 must face down

*205

203*

214

213*

220*

DO NOT ALLOW

THIS NUT TO MOVE

WHEN INSTALLING

PISTON ONTO ROD

211*

*212

219*

TORQUE TO
80 ft–lb
(107 N.m)

221

221