A well-known example of 
the deformable gasket is the old- 
fashioned rubber disk overlying the 
drain and serving as a stopper in a 
bathtub (Figure 69a). A high-pressure 
example is shown in Figure 69b. The 
common noncritical application (so 
far as dimensions are concerned) 
found universally is the O-ring, 
usually made of a pliable elastomer 
but useful for higher pressures when 
made of harder materials. A common 
loose-fitting section conforming to 
one manufacturer's design criteria is 
shown in Figure 70. In 70a it is 
shown unpressurized as it might be 
at time of assembly, at one atmo- 
sphere. In 7Ob the same gasket is 
shown under pressure with extrusion 
into the clearance spaces exaggerated. 
The only requirement for successful 
operation is that the joint be placed 
under sufficient pressure to drive the 
gasket against the seating surfaces— 
at too low a pressure, leakage will 
occur indefinitely. In this respect, such a gasket is inferior to the earlier 
compressed forms, which were useful at no pressure as well as elevated pres- 
sures within limits. For static applications, O-rings are frequently placed under 
slight compression to Insure rapid seating. They are also fairly successfully used 
in nonpressure applications, in which case they require heavier initial compres- 
sion and are usually confined in a small groove. 
A recent and timely paper by Mikesell and Brown (1968) discusses the 
problems at some length, although in slightly different context than the above. 
For very high pressures, they analyze and discuss the success of a proprietary 
gasket (Figures 71 and 72). Whether this configuration would be optimum 
for sealing large openings to the undersea base is questionable, because it 
may not be well adapted to repeated opening and reseating. It may, with 
minor modification, be useful in solving the larger problem discussed below. 
elastomer in 
compression 
Figure 68. Conventional compression 
gasket. 
91 
