How to change a hydraulic breaker seal kit: the work order and common mistakes

Three decisions before you start

This guide covers how the change is done. Which symptom calls for a seal kit and which for a service kit is in the service kit and seal kit guide, and why changing seals alone fails when a worn bushing is behind the leak is in the bushing wear guide. Strip-down starts once those two decisions are made.

• Where: an area free of dust where the removed parts can be laid out on a clean surface. If you cannot set one up, sending the breaker to a workshop costs less than filling an open body with dust.
• Tools: a torque wrench, the breaker’s own nitrogen charging kit, non-metallic tools for removing and fitting seals, clean hydraulic oil and lint-free cloth. On large models you also need lifting gear to remove the piston and separate the body.
• The right kit: a kit is ordered by the breaker’s brand, model and serial number; seal sizes can differ between versions of the same model. We covered what the order needs in the guide to ordering spare parts.

Safety: the body is never opened before the nitrogen is released

The back head of a breaker holds pressurised nitrogen, and on models with an accumulator there is gas inside the accumulator too. If the tie rods are loosened before the gas is released, the nitrogen acts like a spring pushing the body sections apart and the last tie rods to be loosened end up under heavy load. The gas is released with the breaker’s own charging kit, following the method in the manual.

The second risk is hydraulic. Before the breaker comes off the machine, the line pressure is released and the couplings are capped. We covered the removal order in the fitting and removal guide.

The change, step by step

1. 1

   Remove the breaker and clean the outside

   Take the breaker off the machine, cap the ports and wash and dry the outside before opening the body. Any mud left on the outside falls inside the moment the body separates.

2. 2

   Release the nitrogen and any accumulator gas

   Fit the charging kit and release the nitrogen following the manual. On models with an accumulator, release the accumulator as well. Do not move on until the gauge reads zero.

3. 3

   Remove the tool and the retainer set

   Take out the retaining pins, their lock and the tool. Look at the tool shank and the bushings now; this is the best moment to measure bushing clearance. We covered how in the bushings guide.

4. 4

   Loosen the tie rods in a cross pattern

   Do not undo the tie rods fully one at a time; loosen them in a cross pattern and in stages. That way the body sections are unloaded evenly and no single tie rod carries the load on its own.

5. 5

   Separate the body and remove the piston

   Separate the back head, cylinder and front head in turn. Draw the piston out parallel to its axis, without turning it and without letting it touch the ground. Look at the piston and cylinder surfaces: deep scoring means the job is no longer a seal change, because the piston and cylinder are assessed together.

6. 6

   Remove the old seals in order

   Take the seals out with a plastic or brass-tipped tool, without scratching the edge of the groove. Lay each seal on a tray in the order it came out; when you fit the new kit, that row is your checklist.

7. 7

   Clean the grooves and compare the kit

   Wipe the grooves with clean cloth and a suitable cleaner, dry them and feel them with a fingertip; a burr or scratch left in a groove cuts the new seal in the first shift. Lay each new seal next to its old counterpart and compare section, diameter and lip direction.

8. 8

   Fit the new seals the right way round

   Wet the seals with clean hydraulic oil or the assembly lubricant the manual recommends. Set the lip direction from the cross-section drawing in the manual and from the old seal you removed, and seat the seal without twisting it. Slide O-rings into the groove rather than rolling them; an O-ring twisted in its groove cannot be seen from outside.

9. 9

   Reassemble and tighten the tie rods

   Oil the piston and insert it parallel to its axis, without forcing. Join the body sections and tighten the tie rods with a torque wrench, in a cross pattern and in stages, to the value in the manual. We covered the sequence in the tie rod guide.

10. 10

    Reconnect the breaker and charge the nitrogen

    Fit the tool and retainer set, connect the breaker to the machine, rest the tool on the ground and release the line pressure. Charge the nitrogen in the position the manual specifies, to your model’s pressure; the value is in the manual or can be obtained from HKM with your model code. Then grease and spend the first hours following the run-in rules.

Common mistakes

• Reusing an old O-ring or seal because it "looks fine". A removed seal has taken the shape of its groove; the saving is paid back with a second strip-down.
• Prising seals out with a screwdriver. The scratch left on the groove edge is where the new seal starts to leak.
• Fitting a seal backwards. A seal with its lip the wrong way leaks within minutes or is pushed out of its groove by pressure.
• Fitting the kit without comparing it with the old seals. A kit for another version often goes in but does not seal.
• Forcing the piston into the cylinder. A piston that goes in at an angle cuts the lip of the new seal.
• Tightening tie rods one at a time to full torque, or using a lever instead of a torque wrench.
• Not looking at the bushing and piston surface while the body is open. If the part that started the leak stays in, the new seal goes the same way.
• Running the breaker at full load in the hardest material straight after reassembly.

The first days after the change

After the first run, check the body joint lines, the tool area and the couplings. A new seal may weep slightly in the first hours; dripping means something went wrong in assembly and work stops.

After the run-in, tie rod torque and nitrogen pressure are checked again; nitrogen is measured with the breaker cold. Write the measured values and the date of the change in the breaker’s record. If the leak returns within a short time, the cause is most likely not the seal but the bushing or the cleanliness of the hydraulic oil; we covered that chain in the damage chain guide.

Ordering the seal kit from HKM

You can see which parts of the breaker the seal kit covers on the seal kit page. Besides parts for its own breakers, HKM makes spare parts to fit more than 130 breaker brands; when the order gives the breaker’s brand, model and serial number, the right kit is identified from that information. Production time for tools and spare parts is 5 working days; complex parts such as cylinders are excluded.

Send your request to sales@hkm.com.tr or use one of the channels on the contact page. You can ask for model-specific values such as tightening torque and nitrogen charging pressure the same way, quoting your model code.