Low leakage plunger assembly for a high pressure fluid system

A fluid control device for use in a high pressure fluid system, comprising:

• a device body including a cavity and a high pressure circuit;
• a plunger positioned for reciprocal movement in said cavity;
• and
• a leakage reduction cap mounted to said plunger in such a manner said leakage reduction cap reciprocates integrally with said plunger for reducing fluid leakage flow, said leakage reduction cap including a base portion extending transversely adjacent an end surface of said plunger and a flexible portion extending from said base portion and positioned between said device body and said plunger, and defining an annular clearance gap between said leakage reduction cap and said device body,
• wherein said flexible portion of said leakage reduction cap resiliently flexes radially outwardly during a compression phase of the plunger in response to fluid pressure forces to reduce said annular clearance gap so as to minimize fluid leakage flow through said annular clearance gap
• wherein said leakage reduction cap defines an annular chamber between said flexible portion and said plunger;
• and
• wherein said base portion of said leakage reduction cap includes a flow passage that fluidically interconnects said high pressure circuit to said annular chamber so that fluid pressure in said annular chamber is maintained substantially the same as pressure in said high pressure circuit.

A fuel pump for use in a high pressure fuel system, comprising:

• a barrel including a cavity and a high pressure fuel circuit;
• a high pressure fuel chamber formed in said cavity;
• and
• a plunger positioned for reciprocal movement in said cavity and operable to move through periodic pumping strokes for pressurizing fuel in said high pressure fuel chamber;
• and a leakage reduction cap mounted to said plunger in such a manner said leakage reduction cap reciprocates integrally with said plunger for reducing fluid leakage flow, said leakage reduction cap including a base portion extending transversely adjacent an end surface of said plunger and a flexible portion extending from said base portion and positioned between said barrel and said plunger, and defining an annular clearance gap between said leakage reduction cap and said barrel,
• wherein said flexible portion of said leakage reduction cap resiliently flexes radially outwardly in response to fluid pressure forces during a compression phase of the fuel pump to reduce said annular clearance gap so as to minimize fluid leakage flow through said annular clearance gap
• wherein said plunger includes a reduced diameter section and a ledge, a distal end of said flexible portion of said leakage reduction cap sealing against said ledge during operation.