Abstract: A hydraulic pump for use in a pump assembly of a railway track lubricating system includes a housing defining an intake chamber having an intake port, an outlet channel leading to an outlet port, a gear chamber containing interengaged gears, a discharge port having a discharge port, a window opening between the gear chamber and the discharge chamber, and a double head piston having a first head in the intake chamber, a second head in the discharge chamber, and a spring for biasing the piston to a first position where the first head is spaced a maximum from a wall between the intake chamber and the discharge chamber. The outlet port has a smaller cross section than the outlet channel so that checked charged deliveries of hydraulic fluid into the intake chamber will cause the piston to move from its first position to a second position and force grease out of the discharge chamber through the discharge port.