Benjamin hand pump high pressure o-ring replacement question.

[Mackie]

I have a Benjamin hand pump that recently failed. I purchased a Captain O-ring replacement kit for it. Tear down went relatively smooth. When I removed the high pressure rod I found a broken white opaque ring that fell out when the rod was removed, a black O-ring was still intact.
Looking at some online videos, they describe a white plastic ring and a black o-ring. I wouldn’t consider the opaque broken ring on mine ‘plastic‘ as it is a low durometer rubber like material.
The Captain O-ring kit instructions only indicate 1 o-ring (clear) goes on the rod. They include 2 black O rings in the kit and the clear polyurethane ring, all 3 the same size. See pics.
I have a feeling the broken ring I found is not included in the kit and the clear ring is intended to replace the black ring that is still intact. In other words, the only part that really needs replacing is not in the kit.

Thoughts from anybody familiar with this rebuild and/or the Captain O ring kit?
Thanks.

 

[iAMzehTOASTY1]

Are they the same? The black one and the broken one?

 

[nervoustrig]

Where your pump rod has the black O-ring, mine had a rigid plastic ring. Other brands I've worked on have had the same sort of thing. This part serves the role of a backer ring...being a square cross-section, it supports the polyurethane O-ring on the compression stroke (down stroke).

The black O-ring in that position is presumably less good at that role but I see in the Sun Optics rebuild guide they recommend that arrangement so I say go with it.

In summary, I would remove the old black O-ring and install one of the new black O-rings followed by the polyurethane O-ring.

 

[Mackie]

Where your pump rod has the black O-ring, mine had a rigid plastic ring. Other brands I've worked on have had the same sort of thing. This part serves the role of a backer ring...being a square cross-section, it supports the polyurethane O-ring on the compression stroke (down stroke).

The black O-ring in that position is presumably less good at that role but I see in the Sun Optics rebuild guide they recommend that arrangement so I say go with it.

In summary, I would remove the old black O-ring and install one of the new black O-rings followed by the polyurethane O-ring.

Thank you! I searched for Sun Optics instructions and it’s exactly as you described.

 

[Mackie]

One last question, other than a complete o ring kit (most of which don’t need replacing), is there a source to just buy the high pressure rod O-Rings since it appears this will be the high replacement part?

 

[nervoustrig]

Disogrin cast polyurethane (90 durometer) in particular is the most durable

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