Can I mix brands in one cylinder?

Not recommended — use one matched kit.

Why Cheap Hydraulic Seal Kits Fail Early: Shore Hardness and Quality Checks

Q: Is PU always better than NBR?

For dynamic high-pressure seals yes; static O-rings use NBR.

Q: How long should a quality kit last?

Close to original life with clean installation.

Home › Knowledge Base › Seal Kit Quality Guide

Short answer: Nine out of ten early seal failures are a material or hardness problem, not bad luck. Pressure seals need PU (polyurethane, 90–93 Shore A); static O-rings use NBR. Before buying, check five things: material, hardness, lip finish, packaging, and whether the seller can name the original part number the kit replaces.

The 5-point quality check

Check	Good	Bad
Material	PU on pressure seals, NBR on static O-rings	All-black rubber, material not stated
Hardness	90–93 Shore A on rod/piston seals	Soft and floppy (around 70 A)
Lip finish	Clean trimmed, chamfered lips	Rough flash, torn lips
Packaging	Labeled bag per kit, part number printed	Bulk bin, mixed sizes
Cross-reference	Seller names the original VOE/CAT number	"Fits everything" answers

Why hardness matters so much

A seal that is too soft extrudes into the pressure gap and chips within a few hundred hours; too hard and it cannot follow rod movement, leaking on the return stroke. Original suppliers tune hardness per position — that is what a "premium" kit actually pays for. We test incoming batches for hardness and only stock kits with a named original cross-reference.

Installation habits that kill new seals

Forcing seals over sharp threads with metal screwdrivers — use a plastic or brass guide.
Dry-fitting cold seals without oil.
Reinstalling onto a scratched rod or barrel — new seals on a scored surface die in days.

Seal kits for cylinders, pumps and motors of all mainstream models — search your number in All Parts.

Frequently asked questions

Is PU always better than NBR?

For dynamic high-pressure seals, yes. For static O-rings NBR is correct — match the material to the position.

How long should a quality kit last?

With correct material and clean installation, close to original service life — thousands of hours, not hundreds.

Can I mix brands within one cylinder?

Not recommended: mixing hardness and profiles inside one cylinder causes uneven wear. Use one matched kit.

Need seal kits that last?

Send the part number — tested batches, labeled per kit, factory price.

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