Abstract: There is disclosed an improved high pressure pump which includes an improved valve system wherein each of the valve assemblies includes a valve housing having a cup-shaped chamber surrounded by an apertured sidewall, an apertured top wall and a defined open bottom wall, the valve housing further including a peripheral continuous flange carried on the bottom end thereof and extending for a short distance outwardly from the valve housing and having a continuous side edge on an outer surface thereof, the outer surface of the continuous flange provided with a continuous shoulder spaced distance inwardly from the side edge of the flange and bounding the defined open bottom wall of the valve housing, and the valve assembly being completed by a valve cap positioned in arrested arrangement within the valve housing and adapted for reciprocating movement such that the valve cap alternately opens and closes the open bottom wall, and further characterized in that the valve housing including the cup-shaped chamber, the pe