shuttles 88 92 apart from one another as shown in fig1 the shuttle 88 is characterized by a protuberance 190 from surface 156 the protuberance 190 contacts a wall of conduit 68 to limit the movement of the shuttle 88 similarly member 194 protrudes from surface 168 of shuttle 92 and contacts a wall of conduit 60 to limit the movement of the shuttle 92 a first mode of valve assembly operation is depicted in fig1 more specifically with the engine 14 and the motor 18 being stopped or off the pumps 42 50 do not pressurize fluid in the passageways 64 72 allowing the spring 186 to bias the shuttles 88 92 in respective closed positions as shown shuttle 88 obstructs ports 96 and 104 to prevent fluid communication between the passageway 72 and therefore the auxiliary pump 50 and the chamber 112 shuttle 92 obstructs port 100 thereby preventing fluid communication between the passageway 64 and therefore the main pump 42 and chamber 112 referring to fig2 wherein like reference numbers refer to like components from fig1 the valve assembly 76 is shown in a second mode of operation more specifically the motor shown at 18 in fig1 is driving the auxiliary pump shown.