How to Identify a Hydraulic Seal Kit When You Have No Part Number
The part number is gone. The decal is unreadable, the manual was lost with the last workshop move, and the machine is already apart on the floor. This is not an unusual situation — it is the normal one.
It is also, in our own catalogue, the majority case. Of 996 hydraulic kit and repair-part listings, 581 carry a part number in the title and 415 do not. In the seals category the gap is wider: of 303 listings, exactly one carries a part number. So the question "how do I order this without a number" is not an edge case for us either.
There are three ways to identify a kit. They are not equally reliable, and knowing the ranking saves a lot of wrong orders.
The three paths, ranked
| Rank | Path | What you need | Reliability | When it fails |
|---|---|---|---|---|
| 1 | Machine model + cylinder position | Make, model, which cylinder | Highest — this is how kits are actually catalogued | When the machine has been modified, or the same model was built in several versions |
| 2 | Measure the old part | Three dimensions of the failed seal | Good, but only if you measure the right part and it is not worn past recognition | When the seal is missing, torn, or so worn the original dimension is gone |
| 3 | Parts book or drawing reverse lookup | A parts book, a drawing, or a photo of the stamped number | Depends entirely on the document being correct for that machine | When the document is for a different serial range |
The practical order is 1 → 2 → 3. Use the model first, use measurements to confirm, use documents only when the first two are blocked. Most failed identifications happen because someone started at 3, or jumped straight to 2 without ever stating the model and position.
Path 1: machine model plus cylinder position
This is how seal kits are actually organised, on our site and everywhere else. A kit is not a generic set of rings; it is the set of rings for one specific cylinder on one specific machine.
So the two facts that matter most are:
- The machine. Make and model, as precisely as the plate allows. "PC200" and "PC200-7" are not the same order. Serial prefix helps when the same model was revised.
- The cylinder. Boom, arm, bucket, steering, lift, tilt, outrigger, stabiliser, quick-coupler. "The main one" is not a position.
If you have those two, you can usually stop. Our seal kit lookup by machine model is built around exactly this pair of inputs.
Where this path fails. Modified machines, machines assembled from parts of two models, and models that were revised mid-production without a clear serial break. In those cases the model points to the right family but not necessarily the right kit, and you need path 2 to confirm.
Path 2: measure the old part
Measuring works, but only if you measure the right thing and understand what the number means.
Take three dimensions, in this order:
- Inner diameter — the sealing edge, measured across the inside of the lip
- Outer diameter — across the outside of the part as it sits in its groove
- Height (or cross-section, for an O-ring) — the axial thickness
Write them in the order ID × OD × height. This is the convention used in catalogue listings, so a supplier reads it without asking. You will see it in our own titles — for example p175 is listed as a DHS dust-proof oil seal at 50x58x5/7, which reads as 50 mm inner, 58 mm outer, 5 mm height with a 7 mm overall lip.
Three warnings about measuring:
- A worn seal measures small. The lip has been rubbed away, so the inner diameter you read is not the original. If the part is heavily worn, your measurement is a lower bound, not a specification.
- A swollen seal measures wrong in a different direction. Material that has absorbed oil can read larger than it was. This is common with old NBR parts.
- A torn or missing seal cannot be measured at all. In that case go back to path 1, or measure the groove instead — but measuring a groove requires knowing which dimension of the groove matters, which is a separate subject: how to measure a seal.
Also state which part you measured. "55 × 70 × 12" means nothing until you say whether that was the rod seal, the wiper, or the piston seal. A kit enquiry that lists three dimensions without saying which parts they belong to usually produces a follow-up question, which costs you a day.
Path 3: parts book or drawing reverse lookup
If the machine has a parts book, the cylinder is listed as an assembly with its own part number, and the seal kit is usually a single line item under it. That is the fastest route when the book is correct.
The failure mode is a book for the wrong serial range, or a photocopy of a photocopy where one digit has been read wrong. Check any number you extract against a second source before ordering.
There is also a version of this path that works from the part side: if the old seal has a stamped or moulded number on it, that number can be looked up. It is worth a look before you throw the old part away — but be aware that the number on a seal is often the seal manufacturer's own number, not the machine maker's, and the two live in different catalogues.
For how part numbers cross-reference in practice, see seal kit cross-reference by part number.
The description template
Copy this into your enquiry. Fields marked required are the ones that decide whether the answer is right; the rest shorten the exchange.
| Field | Required | What to write |
|---|---|---|
| Machine make | ✅ | e.g. Komatsu, Hitachi, Caterpillar, Kobelco, Doosan, Volvo, JCB |
| Machine model | ✅ | as complete as the plate shows, including any suffix |
| Cylinder position | ✅ | boom / arm / bucket / steering / lift / tilt / outrigger |
| Quantity | ✅ | how many kits per position |
| Part number | ➖ | if you have one, even partial |
| Old part dimensions | ➖ | ID × OD × height, and which part it was |
| Material on the old part | ➖ | if it is marked or identifiable |
| Photos | ➖ | old seal next to a ruler; the rod surface; the gland; the machine plate |
| Symptoms | ➖ | leaking, drifting under load, slow in one direction, sat unused for a long time |
| Rod condition | ➖ | scored / polished / rusty / unknown |
Two things make a template enquiry work better than a free-text one: it forces the model and position to be stated, and it makes missing information visible to both sides instead of being discovered three messages later.
A worked example: what a part number actually buys you
p147 is listed as a lift cylinder seal kit for Caterpillar D8R and D8T crawler dozers. The listing carries five reference part numbers: 240-1881, 238-8157, 240-9538, 242-2539 and 244-2067.
Note the word reference. These are numbers the listing associates with the kit — they are not a claim that they are the original manufacturer's numbers, and on this site they are labelled as reference numbers precisely because that distinction matters. What they do is give a buyer something to check against: if your old paperwork shows one of those five, you have a match without measuring anything.
That is the value of a part number in one line: it replaces three measurements and a guess about which cylinder.
For contrast, p326 is listed as a PC200-7 boom cylinder seal kit, with no part number at all. That listing works purely on model plus position. Both approaches are legitimate; the first is faster when the number survives, the second is the only option when it does not.
Four descriptions that fail
- A photo with nothing for scale. A seal photographed on a desk could be 20 mm or 80 mm across. Put a ruler or a coin in the frame.
- "One set of seals for the cylinder." Which cylinder, on which machine, how many.
- Trade names instead of positions. "Oil seal" and "rubber ring" are used for at least four different parts. Say where it sits.
- Dimensions with no part identity. Three numbers alone cannot be turned into a kit.
What happens after you send it
You get one of three answers: the kit is matched from the catalogue; the kit needs confirming against a measurement you have not sent yet; or the cylinder is not one we carry and we say so.
The third answer is the one worth insisting on. A supplier who never says "we don't have it" is not checking. We would rather tell you we cannot match a cylinder than send a kit that is close.