o-ring calipers

[Greg L.]

This might be a dumb question but how can these actualy seal?? I mean, I was always under the impression that to have a good seal there had to be a lip of some kind for the pressure to build against thus forcing the sealing surface(lip) against the wall, not unlike the compression rings of an engine. To me the o-ring design would in fact let the pressure get "behind" the o-ring and try to push it away from the wall. I'm not disputing the fact that o-ring calipers are better, I'm just a little baffled at why they are better. Anyone want to fill me in on this? Thanks again.

[Joe L.]

Re: o-ring calipers

Greg-----

I understand your concern; it's one of the things that's always bothered me about o-ring style calipers, also.

A lot of the efficacy of o-ring calipers depends on a very tight piston-to-bore clearance. Without that, the o-rings would not stand a prayer of sealing. Beyond that, keep in mind that the o-ring piston seal design is NOT new. It's been around since the 60's for other applications and forms of it are still used today for MANY modern applications. In today's world, brake pistons which use a "square" cross section piston seal are everywhere. C4, C5, and C6 Corvettes use that configuration seal, so the basic "o-ring" design is pretty well "tried-and-true". Also, most hydraulic cylinders used on construction equipment use o-ring seals. In fact, I was just watching a big Koehring 1266D hydraulic excavator with DUAL 12V-71 GMC diesels work this afternoon and I was thinking just how much pressure that those o-ring seals in the hydraulic cylinders have to bear.