Sakagami Seal Installation Instructions

Sakagami packings, wipers, bearings and cushion seals are supplied for one-piece (continuous) grooves unless the drawing states otherwise. Almost every fitting problem on a hydraulic cylinder comes down to the same three causes: too much deformation, the wrong entry direction, or a sharp edge somewhere on the path. This page sets out the installation method profile family by profile family.

General rules

• Deburr and chamfer every edge the seal passes over; break the chamfer tip with a small radius.
• Grease the groove and the seal lightly with a fluid-compatible lubricant before fitting.
• Keep deformation to the minimum needed to get the seal over the shoulder, and hold it deformed for as short a time as possible.
• Never fit a seal with a screwdriver or any hard-edged tool. Use fingers, a plastic jig, or a mounting sleeve.
• Check the lip orientation before pushing home — a reversed U-packing or wiper will leak from the first stroke.
• Allow a recovery period after fitting where the profile has been heavily deformed, before pressurising.

1. Installing packings

1-1 U-packings and similar profiles

1. Piston packings: hook one side of the packing into the groove, then extend the opposite side and push it over the piston shoulder into the groove.
2. Rod packings: deform the packing into an ellipse (kidney shape), slide one side into the groove and work the remainder in with the fingers from the opposite side.
3. Small sections: use an installation jig rather than fingers — small-bore packings take permanent set very quickly when over-deformed.

1-2 ST and STK seals

These are two-part sets: a PTFE-based slipper or seal ring energised by a rubber back ring.

1. Fit the back ring (O-ring or square ring) into the groove first.
2. Hook one side of the seal ring onto the groove.
3. Push the opposite side in from the tapered side of the ring.

1-3 PG rings

• Piston: hook one side of the ring in and push the opposite side into the groove.
• Rod: deform the ring into a kidney shape, insert one side, then push the remainder home while holding the ring with the fingers.

1-4 SMJ seals

1. Fit the rubber back ring (O-ring) first.
2. Deform the seal ring into a kidney shape, insert one side and push the remainder home.
3. Check the direction of the seal ring — SMJ seals are directional and will not seal if reversed.
4. Minimise deformation of the seal ring throughout.

1-5 Rotary joints (STK / STR seals)

Multi-groove rotary joints are the hardest Sakagami installation, because each seal ring must travel past every groove and drain port above its own.

1. Fit a single back ring (rubber square ring) into the lowest seal groove only.
2. Move the seal ring down through the upper seal grooves and drain ports to its groove.
3. Hook one side of the seal ring into the groove and push it quickly across to the opposite side, sliding it on the radiused or tapered section.
4. Repeat for the second and subsequent grooves, working upwards.

• Never fit more than one back ring at a time — always install a seal ring and its back ring as a pair.
• At the design stage, radius the drain-port edges (R2–R3) and keep the groove pitch narrow so seal rings slide freely.
• Where the distance from the end face to the first groove is long, provide a waste channel to guide the seal ring.
• Set the drain-port depth in the same plane as the seal grooves so the ports themselves act as sliding channels.

2. Installing dust seals and wipers

SDB press-in with inner peripheral guide

1. Insert the SDB inner peripheral guide into the rod cover (housing).
2. Fit the wiper onto the guide and push it gently into the rod cover.
3. Place the pushing jig onto the guide.
4. Press the jig home with a hand press.
5. Remove the pushing jig, then the inner peripheral guide.

SDB press-in with pushing jig guide

1. Push the wiper gently into the rod cover.
2. Place the pushing jig and jig guide onto the shoulder of the wiper.
3. Press home with a hand press.
4. Remove the jig and guide.

3. Installing bearings and wear rings

• Fit the S-LEEVE bearing before any packing or wiper.
• Rod S-LEEVEs above ø45 mm: deform by hand and insert from the dust-seal side.
• Rod S-LEEVEs ø40 mm and below: insert from the pressure side using a fitting jig.
• Piston S-LEEVEs and wear rings are cut at one point on the circumference — open the cut and spring them over the piston.
• Fit PWL bearings last, after all packings are mounted.
• Keep deformation to a minimum throughout; bearing strip does not recover like an elastomer.

4. Installing cushion seals

In all three cases, minimise deformation during fitting. Cushion seals run at high local velocity and any permanent distortion left from installation shows up as uneven cushioning at the end of stroke.

Post-installation checks

• Confirm every lip faces the pressure side and no seal is twisted in its groove.
• Rotate or stroke the assembly by hand before pressurising to confirm nothing is trapped.
• Commission at low pressure first; step up in stages rather than applying full working pressure immediately.
• Re-check for weeping after the first thermal cycle — installation damage often shows only once the seal has run warm.