The “PTO valve” is similar to the analog unit, except it is a four-way pressure control. This patented valve is designed to modulate pressure on two separate functions as command is increased. As shown in the schematic, supply pressure is connected to the brake control port at zero command. As command is increased, the brake port is modulated off proportionally, and then the clutch port is modulated on proportionally. This means these two separate functions are locked out from one another and controlled by a single command (see gain curve).
PTO stands for “power take off,” and as named is used primarily on PTO applications where both a brake and clutch are used to disengage and then engage a function. The ability to modulate the brake is key and results in less aggressive applications when implements are shut down.