Abstract: A multi-valve, multi-port, relay device used in a control system for sequentially pressurizing a first reservoir before a second and depressurizing the second reservoir before the first. A piston valve configuration for blocking a second outlet permitting an external pressure supply source to pressurize an external reservoir via a first outlet. The piston is biased in the second outlet blocking position by a spring having a force preselected by the operator via an adjustment screw. A pressure force greater than the piston spring biasing force opens the piston valve configuration. When open, the piston valve configuration and a check valve configuration cooperates to block flow out of the first outlet, but permit flow out the second outlet to a second external reservoir, until full pressurization. An overpressurization feature enables the bleed off of pressure increases associated with thermal expansion of the working fluid.