Patent ID: 8388326

Claim:
A piston pump assembly comprising: a first pump including a first cylinder member inserted in a piston hole and defining a pump chamber, and a first piston having one end portion thereof axially slidably inserted in said first cylinder member so as to protrude into said pump chamber; a second pump including a second cylinder member inserted in the piston hole, and an annular second piston axially slidably fitted in an annular groove formed in an outer periphery of said first piston, and also axially slidably inserted in said second cylinder member; said first cylinder member axially pressing said second cylinder member, thereby preventing the second cylinder member from being dropped out of the piston hole; wherein said second cylinder member has an annular seal surface kept in contact with an axially facing shoulder surface formed on an inner periphery of the piston hole, thereby sealing between inner and outer peripheries of said second cylinder member; wherein strain-absorbing protrusions made of a material softer than said first cylinder member are provided at one end of the second cylinder member remote from the annular seal surface said strain-absorbing protrusions being configured to be axially compressed and deformed when said strain-absorbing protrusions are pressed by the first cylinder member; wherein said second cylinder member has an annular peripheral wall in which a plurality of circumferentially spaced apart openings are formed to extend from inner to outer peripheries of the annular peripheral wall, said openings constituting fluid intake passages through which fluid is drawn into a feed chamber of the second pump; and wherein said strain-absorbing protrusions protrude axially in the direction in which said one end portion of said first piston portion protrudes into the pump chamber, and wherein said strain-absorbing portions are provided at positions corresponding, respectively, to portions of the annular peripheral wall connecting together the respective adjacent pairs of openings.