open when the fluid within compression chamber 48 bore reaches a predetermined level when the operating fluid reaches the predetermined pressure check valve 36 will open to allow the pressurized fluid to flow from compression chamber 48 hydraulic pump 20 may include a collector 38 pressurized operating fluid that is released from each compression chamber 48 through check valve 36 may be directed to collector 38 collector 38 may be configured to store a desired quantity of pressurized operating fluid collector 38 is connected to an outlet 24 which may be further connected to an outlet line 18 outlet line 18 may be connected to a fluid rail 19 fluid rail 19 may be configured to distribute pressurized operating fluid to a system such as for example a fuel injection system associated with a vehicle and or engine as also schematically shown in fig1 hydraulic pump 20 includes a series of metering sleeves 34 one metering sleeve 34 is associated with each piston 32 and cylinder 46 combination as described in greater detail below each metering sleeve 34 is configured to control the rate at which pressurized fluid is generated by the respective piston 32 as illustrated in fig2 a 2 b and 3 metering sleeve 34 includes.