ericm979
Super Member
- Joined
- Nov 25, 2016
- Messages
- 5,752
- Location
- Santa Cruz Mountains CA, Southern OR
- Tractor
- Branson 3725H Deere 5105
The reason why you plumb into the PB port to feed downstream valves is that when those valves are powering something (like a cylinder) the pressure to do the work flows through each valve in sequence. So if your 3rd function valve is closing a grapple, the pressure to do the work comes from the pump through the loader valve, out its PB port, into your 3rd function valve and then out to the cylinders.
For a lot of manual valves the tank port can only handle 600 psi or so, not the 2200 or so that your loader valve's relief is set at. The PB port can handle the pressure.
For some reason I don't understand, the usual solenoid valves that are used to make a 3rd function using two buttons on the joystick have tanks ports that can handle full pressure, and no PB port. Some manual spool valves are also set up that way but most have a low pressure tank port and need a PB port and sleeve to feed another valve.
BTW when the loader valve on my Branson 3725 is operated even just a little it cuts off flow to the PB port. Everything that does not go out a work port goes to tank. So you can't move the loader and also open/close the grapple with a 3rd function that's plumbed in after the loader valve. Your tractor may be the same.
For a lot of manual valves the tank port can only handle 600 psi or so, not the 2200 or so that your loader valve's relief is set at. The PB port can handle the pressure.
For some reason I don't understand, the usual solenoid valves that are used to make a 3rd function using two buttons on the joystick have tanks ports that can handle full pressure, and no PB port. Some manual spool valves are also set up that way but most have a low pressure tank port and need a PB port and sleeve to feed another valve.
BTW when the loader valve on my Branson 3725 is operated even just a little it cuts off flow to the PB port. Everything that does not go out a work port goes to tank. So you can't move the loader and also open/close the grapple with a 3rd function that's plumbed in after the loader valve. Your tractor may be the same.