temperature of approximately 140 degrees f when the selected temperature is exceeded the valve will divert the water back into the inlet 204 to avoid applying too much internal pressure to the pump body 92 the outlet 214 is equipped with a standard high pressure hose connector for coupling to a high pressure hose not shown the structure of the unloader valve assembly can be better understood by referring now to fig8 fig8 is an exploded perspective view of a preferred unloader cartridge assembly of the present invention the unloader valve assembly 208 includes a piston 216 and four piston rings 218 220 222 and 224 which are preferably formed of polytetrafouroethelyne or ptfe plastic a spring 226 is mounted onto the shaft portion 227 of the piston 216 which applies a force against valve seat 228 o ring 230 is positioned between valve 232 and seat 228 in operation water travels into the cavity 238 as best shown in fig7 the water enters into a central bore of the piston 216 by means of opening 236 shown in fig8 and travels through a venturi not shown causing a pressure drop as long as the pressure differential is present the water travels through the valve and out the outlet 214 when the outlet 214 is blocked the pressure differential in the valve disappears and the water is diverted through channel 238 and back into the inlet 204 this type of unloader valve 208 is particularly useful in connection with a water gun of the type known in the pressure washer industry.