Gasket vs. O-ring (Hydraulic Design Question) - Practical Machinist

You guys have been a good resource in the past for practical mechanical questions.

I'm starting a design on a sort of porta-power jack (hence, it's not a dynamic hydraulic scenario)...just has to hold pressure for long periods of time. For manufacturing purposes I will need to have a part interface that's either an o-ring seal or a gasket. I'm now thinking that a gasket would make more sense (since the part's an odd profile) and I can be more sloppy in the tolerances than with an o-ring and a chance of failure is reduced.

Anyone have luck with gaskets in a hydraulic oil environment, and if so, with what gasket material? The max. psi would be lbs static. Matt,
All the o-ring mfgr's data I've ever seen calls for grooves with straight sides. I think the walls can taper something like 2* to wider at the top, but that's optional. Some designs do also use a groove with a full radiused bottom, and while standards for that design may be spec'd out somewhere, I've never seen it in print. One of the main things to remember when deviating from a standard set of dimensions is that you have to provide crush space within the groove. If the assembly provides less cross section than the c.s. of the o-ring, then the o-ring will extrude. IOW, they change shape readily, but, like water, their volume doesn't decrease nearly so readily.

When you have a face seal situation, such as a cylinder with a flanged head, then the bolt tension at installation becomes critical. You have to assure that the bolts are sufficiently tensioned such that they'll not see any external loading when pressure is applied to the cylinder. If the bolts are allowed to stretch within their elastic range via application of pressure, then it becomes possible for the o-ring to lose part of its preload and leak. This is a major reason why many parts like this employ a spud just long enough to fit into the bore so an o-ring groove on the OD of the spud is used instead of a face groove. With this diametral seal, the bolt tension becomes less critical as regards leakage.

If your porta-power type thing has a piston, I'd recommend using a stack of v-rings (chevron shaped cross section) for the piston seal if it has to hold static pressure for a long time. If you use alternating neo-fab and urethane vees, the assembly will provide good sealing at both low and high pressures. V rings seem to work out better on single acting cylinders in a lot of cases because they aren't as effective as a loaded u-seal in peeling the layer of oil off the cylinder wall. As a result, they will usually collapse more smoothly, and with less stick-slip, when pressure is removed. 4 V's will typically hold psi, while 5 are good for and 6 will take you to 10,000 psi.