Driveroneuk:
Most road vehicle PTO’s I’ve come accross over the past 15 years or so (mostly slide back recovery trucks) have had auto-engage.IIRC the switch is just electric to operate a solenoid which moves the gear into position. Most refuse to engage if the gearbox is not in neutral. (hmmm, how do grit spreaders go on then?)
[/quote]You can have PTO driven by the distribution gears of the valve train, constant engaged, VdB has TRS generators on certain trucks for the cooling motors of reefer conttaines (400V) the hydraulic pump to drive them is built to the front of the engine.
If I remember it right a lot of Dutch garbage collect vehicles have the hydraulics constanly driven by the engine, so the position of the gearbox doesn’t affect them.
If you ever drove away with the PTO engaged on the gearbox you know what I mean.