fyrboy -- *excellent* question!! And it was messing me up to begin with. The "Dump Valve" in this application allows you to dump pressure if you are taking water from a higher pressure source than you are comfortable with. Say, for example, I'm taking water from a city hydrant or from another truck with a 1,000 gpm truck -- this valve allows me to regulate the inlet pressure so I don't over pressure my little 300 gpm pump. It is a simple righty tighty, lefty loosey valve -- for drafting, I have it righty tighty as righty tighty as it can go.
