Vented high pressure shaft seal

A rotary fluid pressure device of the type including housing means having a fluid inlet port and a fluid outlet port;

• a fluid pressure-operated displacement means associated with said housing means, and defining a plurality of expanding and contracting fluid volume chambers in response to movement of a moveable member of said displacement means;
• a valve member cooperating with said housing means to provide fluid communication between said inlet port and said expanding volume chambers, and between said contracting volume chambers and said outlet port;
• an input-output shaft rotatably supported relative to said housing means and drive means for transmitting rotational movement between said input-output shaft and said moveable member of said displacement means;
• a seal assembly disposed radially between said input-output shaft and said housing means, and cooperating therewith to define a pressurized case drain region;
• characterized by said seal assembly comprising, in the order of the direction of leakage flow from said pressurized case drain region;
• (a) a high pressure shaft seal;
• (b) an annular chamber in which is disposed a rigid back-up member disposed adjacent said high pressure shaft seal, said back-up member directly cooperating with a member selected from the group consisting of said housing means, said high pressure shaft seal and said input-output shaft to define fluid passage means;
• (c) a drain passage disposed between said annular chamber and a case drain port, whereby fluid leaking from said case drain region past said high pressure shaft seal flows through said fluid passage means, then through said drain passage to said case drain port;
• and
• (d) a low pressure shaft seal.