Cross-referencing OEM seal part numbers to a local source

A foreign-invested plant running Japanese equipment, reading German drawings and buying its supplies in Vietnam almost always holds three part numbers for the same part. The drawing carries the equipment manufacturer's number, the stores carry the number of the approved supplier, and a third supplier quotes a third number. The work is to establish whether those three numbers really are the same part, and to record the basis for next time.

Step 1: separate the equipment maker's number from the seal manufacturer's number

The number printed on the seal rim is the seal manufacturer's number. The number in the equipment maker's spare parts catalogue is usually a repackaging number: the same seal, a different label, a different price.

This matters because the two numbers return two different results. Searching the equipment maker's number normally leads back to that equipment maker alone. Searching the seal manufacturer's number opens up the whole replacement market.

How to separate them: take the old part out and read the marking stamped on the rim, or look up the equipment maker's number in the technical documentation to find the tier one supplier.

Step 2: check the fitting dimensions first, but do not stop there

The three figures d x D x B have to match exactly. That is the necessary condition and it is the easiest one to check.

But matching dimensions prove only that the part fits the space. They say nothing about how long that part will last under those particular operating conditions. The four properties below are what decide:

• Lip material. NBR and FKM in the same size and the same shape differ by a full hundred degrees C in operating limit.
• Lip configuration and spring. Single lip or double lip, garter spring or none.
• Case type. A fully rubber-covered case or an exposed steel case. It decides whether the seal can take up a worn housing bore.
• Tolerance class. The same size series with a different tolerance class gives a different interference fit into the housing bore.

Step 3: grade the equivalence, do not merge it into one column

A cross reference table with a single "equivalent" column is a table the quality department will send back. Three levels can be kept apart:

• Direct replacement. Dimensions, material, lip configuration and case type all match. The change needs no further paperwork.
• Functional equivalent once the material is confirmed. Shape and dimensions match; the material has to be checked against the medium and the temperature at the fitting position.
• Verify before use. One property that bears on service life is different. Run it on a non-critical position before extending it further.

The Cross reference table on a KIT part page is written to these three levels, and the level for each row sits in the table itself rather than being inferred.

Step 4: change one variable at a time

When you change source for a position that is running steadily, keep the material and the lip configuration unchanged on the first change. Change the supplier only.

Change source and material at once and a failure cannot be traced to a cause: the conclusion usually settles on "a poor replacement part" even though the real cause may be that the new material does not suit the medium.

Record the date of the change, the fitting position and the running hours to the next replacement. After two cycles you have data to decide on instead of an impression.

The record to keep for every cross-referenced number

At minimum: the original number, the replacement number, the equivalence level, the basis for the cross reference (which document, which page), who confirmed it and the date. Without the basis, a cross reference table is only a list left behind by whoever came before, and the next person has to start again from the beginning.

Further reading: three standards systems on one seal and the documents required to open a supplier code. The oil seals catalogue lists the sizes currently available together with the cross reference table for each number.