Is the plug a solid plug?
What is the fit in the cylinder ?

I'm guessing process contamination from those lubes is no porblem.

Hi T

yes, it's a solid Viton plug, 1/2" dia x 1/2" long and is pressed into the bore with ~ .003" diametral squeeze.
no process contamination from any of the ones listed. we have used Krytox in the past with excellent results but does not stay forever - looking for a hard coating to cover the CDA 360 brass and become more permanent...

Did you burnish the brass first so that it had a surface that layed in the axial direction?
Perhaps you are using too much interference?
When the plus slides is it being pushed, so that it is trying to expand more?
Wouldn't a plug with raised seals at both ends be more effective?
The problem with a coating is that the brass is so soft that over time it will not support it.
A relief in the center of the plug would also allow for a small reservoir of Krytox.

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P.E. Metallurgy, consulting work welcomed

Presumably the plug has some other requirements beyond reciprocating.

It's not possible to provide constructive suggestions without knowing the complete set of requirements and constraints.

Hi Ed,

No not burnished but reamed to a 32uIN finish.
The people @ General Magnaplate state the coating Nedox PF-F is 65Rc. Does that help?

Nope, not when the brass is only 60HRB, not enough support.
I would look at methods to longitudinally polish the ID.
There should be no circumferential marks, unless you hone and leave a nice diagonal crosshatch.

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P.E. Metallurgy, consulting work welcomed

With a coating, it may not be necessary to use brass and a harder material can be substituted.

Thanks guys...

Mint - you are correct - the application requires the Viton plug to be pushed into the bore lifting a ~ 5lb load via a piston on the other side. It has been performing fine for years but we noticed recently a "stickage" issue where if sat idle for months there's a breakaway friction issue with the Viton plug where the 5 lb load isn't enough to overcome and return to retracted position

Ed / TBE - next step for us would be 303SS - is that hard enough?

One advantage of a 300 (or 200) SS would be that if you built it and then cycled it a lot, as you get some surface wear you would also get some surface hardening.
We used to make some sleeves in Nitronic 50 and break them in with a very hard rubber plug (ours rotated). We would run them roughly equal to the expected service life (but sped up of course). Then in service with the softer seal plug they worked very well without coatings.
303 will always have a slightly rough surface, which could help you (less surface contact and lube retention), or it could hurt you (tearing of the rubber). It isn't very good for coating because of the large inclusions in the structure.

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P.E. Metallurgy, consulting work welcomed

Thanks Ed,

Next stock material we use is 316L SS or 2507 Duplex SS. Any better?

Btw - 303SS sure seems to look like a material best used for non-critical service components like handles etc LOL…