5 replies to this topic

[ChiliPepperFender]

Before I posted a topic about what lubricants to use, I had (stupidly) used a petroleum based spray one that totally F-d up one of my SMDTG pumps. Although, instead of the lubricant "eating away" my o-ring, which many had told me, it has actually expanded it. Doing this thus made it terribly hard to pump the gun. My question is, is this normal? Also, this may sound stupid, but, should I add a lubricant to my expanded o-ring to try to shrink it down? I'm not sure if this would work at all. But I would like your suggestions.
Thanks

Edited by ChiliPepperFender, 29 March 2008 - 11:01 PM.

[CaptainSlug]

1. it has actually expanded it. Doing this thus made it terribly hard to pump the gun. My question is, is this normal?
2. Also, this may sound stupid, but, should I add a lubricant to my expanded o-ring to try to shrink it down? I'm not sure if this would work at all. But I would like your suggestions.
Thanks

1. Yes it's normal. The o-ring is also a petroleum product and will slowly soak up the petroleum based lubricant. Normally Buna-N can resist petroleum oil alone, but petroleum based lubricants tend to include strong decreasing agents and penetrants. These help the lubricant by pass the chemical resistance properties of the o-ring. The petroleum based lubricant will degrade the o-ring over time.
2. The chemical reaction process is not reversible by any means. You will have to replace the O-Ring.

PTFE, FET, and fluorosilicone are typically the only material of o-rings that you can use safely with petroleum based lubricants. They are expensive and really only used for high precision valves.
WD-40 however SHOULD NEVER be used on any constant-wear parts. It was originally designed as a combination rust breaker and degreaser so it has some extremely strong compounds that will eat anything if it's left there long enough.

The list of industry recommended o-ring specific lubricants is very short.

Silicone: Use with virtually any rubber polymer including Buna-N, neoprene, and Viton.
Barium Based: Use with synthetic rubber seals in low-pressure pneumatic systems.
Molykote 55: Not recommended for O-rings or seals made of silicone rubber, polycarbonate, or ABS thermoplastic.

Edited by CaptainSlug, 30 March 2008 - 12:24 AM.

[ChiliPepperFender]

Hey thanks for the help Sluggy, wow you know alot. Also, I can't believe I never realized to just replace the o-ring.

[CaptainSlug]

Hey thanks for the help Sluggy, wow you know alot. Also, I can't believe I never realized to just replace the o-ring.

Some hardware stores sell them individually for less than a dollar. Finding an exact match usually isn't a huge issue because stock guns tend to come with very loose fitting o-rings. Getting one with an identical cross sectional diameter is more important than getting one with the diameter measurements of the stock o-ring.

[ChiliPepperFender]

Yeah, I've gotten alot of o-rings before for longshots and nitefinders so I'll be fine. Thanks for all your help though.

[Captain]

Too bad about the O-ring. One of my SMDTG's was hard to pump, and upon opening it up, I discovered that there was NO lubricant on the pump at all. I used a tube of grease from this kit I got one time. (The kit was for building a small tracked vehicle chassis) And now, it works fine.