of the upstroke the injection fluid at pressure p i is present in the following inlet passageway 128 inlet 48 bore 94 of shaft 92 cup member 104 valve chamber 50 between the valve and adjacent portions of shaft 92 the lower righthand generally l shaped section of the valve chamber 50 located below valve member 106 the lower lefthand region of valve chamber 50 located below valve member 106 passageway 66 annular passageway 68 between sealing rings 84 and 86 lateral passageways 70 and 72 check valve 118 and the area within chamber 58 below piston 102 lateral valve bore 110 passageway 76 and the region within chamber 54 below piston 100 low pressure fluid at pressure p l is present in the following passageway 74 and the region of chamber 54 above piston 100 passageway 82 and annular passageway 80 between sealing rings 84 and 88 dog leg passageway 70 openings 126 the annular space between sealing rings 122 124 and outlet slots 34 finally high pressure fluid at pressure p h is present in the following the region of chamber 58 above piston 102 check valves 114 116 and 120 passageways 83 and 83 a chambers 60 and 62 check valve 130 the region below the assembly 26 and in the annular space between tubular wall 46 and nipple 24 up to the level of seal 124 as the injection fluid is delivered to engine piston chamber 54 the piston 100 is moved upwardly owing to the fact that the fluid above the piston 100 is at the lower pressure p l below p i.