15-6850-08 is the inner piston back-up washer on the Wilden T15 (position 18), made from mild steel — small, cheap, and easy to skip by mistake.
| Material | Mild steel |
|---|
Position 18 on the T15 parts list is a small piece of hardware that rarely gets a second thought: the inner piston back-up washer, part 15-6850-08, made from mild steel. Its job is to spread clamping load evenly and keep the piston assembly properly seated — not glamorous, but it matters more than its size suggests.
Washers like this get skipped during rebuilds more than almost any other part, mostly because a flattened or slightly corroded one doesn’t always look obviously bad sitting on a bench next to the tools. It usually takes a side-by-side comparison with a new one to see the difference, and by the time it’s visually obvious, the joint it was supporting has often already started working loose.
During a full T15 rebuild, swapping it out regardless of how it looks is one of the cheapest insurance moves available — and it’s worth ordering the exact part number rather than grabbing a generic equivalent, since thickness and material can differ just enough to matter under repeated load.
Washers like this usually come up during a fuller air-end rebuild — if the pump has also been cycling unevenly, it’s worth starting at the air valve assembly.
Genuine Wilden AODD Diaphragm Pumps & Spare Parts15-3210-55-225 is the PTFE Glyd Ring sealing the T15’s shaft at the center block. A high-wear part on any pump running heavy duty cycles.
Genuine Wilden AODD Diaphragm Pumps & Spare Parts15-3100-01-225 is the aluminum center block on the Wilden T15 — the hub that the air valve, shaft and both chambers all attach to.
Genuine Wilden AODD Diaphragm Pumps & Spare Parts15-3800-09-07 is the shaft connecting the T15’s two diaphragms through the center block. Why it matters more than its simple job suggests.
