Abstract: A high pressure pump comprising a valve body having a first housing secured at one of its ends to one end of the valve body and having a body member secured to the other end thereof. A second housing is secured to the body member with a piston rod movably extending through the body member and the first and second housings. A first piston secured to the piston rod and movably positioned in the first housing defines first and second chambers. A second piston secured to the piston rod and movably positioned in the second housing defines third and fourth chambers. Check valve means are in communication with the third and fourth chambers and sources of fluid to be pumped. The valve body has a pilot valve therein. The pilot valve means is connected to the piston rod so that the pilot valve means will be moved from a first position to a second position when the piston rod moves from a first position to a second position and vice versa. The valve body also has a main valve therein.