Hooking up third function, rear remotes, and a backhoe line.

[TheOldHokie]

[EDIT] I just read the Kubota service bulletin that someone posted a link to. My understanding is that the o-rings in this specific application (i.e. the tank port of the BH) aren't designed to be back pressured and will cause leaks when connected using OP's design.
[/EDIT]

Dan--

Question: What does the PB port on the outlet block do? I'm asking because it seems like it would be for powering some downstream implement. In which case, doesn't the backhoe's tank port still see a pressure every time that implement is used? I'm trying to get a better understand of what the design rule is.

thanks,
Eric

Excellent question.

The return (PB) port on the outlet block is used to power down stream devices like rear remotes and the 3pt.

The "rule" is anytime a valve is providing high pressure carryover (PB) to a downstream device it should have separate carryover (PB) and tank (T) outlet ports. There are multiple reasons for that but back pressure on the upstream tank port is a big one.

Like most rules there are exceptions.

The solenoid operated industrial valves that are commonly used for loader third function can handLe 3000+ PSI on the "T" port so people often use it for high pressure carryover.

Kubota subframe mounted backhoes replace the 3pt lift arms so Kubota cheats and uses a valve without PB and instructs the user to keep the 3pt control kever in the neutral position at all tines. Horrible idea but it saves a few pennies.

Dan

 

[Russell King]

@TheOldHokie
Seems like that question is making the rounds this month! I just asked the same question about a week or two ago.

 

[ejb11235]

Excellent question.

The return (PB) port on the outlet block is used to power down stream devices like rear remotes and the 3pt.

The "rule" is anytime a valve is providing high pressure carryover (PB) to a downstream device it should have separate carryover (PB) and tank (T) outlet ports. There are multiple reasons for that but back pressure on the upstream tank port is a big one.

Like most rules there are exceptions.

The solenoid operated industrial valves that are commonly used for loader third function can handLe 3000+ PSI on the "T" port so people often use it for high pressure carryover.

Kubota subframe mounted backhoes replace the 3pt lift arms so Kubota cheats and uses a valve without PB and instructs the user to keep the 3pt control kever in the neutral position at all tines. Horrible idea but it saves a few pennies.

Dan

Oh wow. I'm glad I asked. And thanks for the explanation.

I think the service bulletin explained why it's ok to drive the PB port on the outlet block using the T output from the backhoe, but I didn't read it carefully enough to fully digest the info.

I have a BX23S, so I don't think the caution about the 3pt lever applies because there are three connections to the backhoe, so I'm assuming it has the full complement of ports.

 

[TheOldHokie]

Oh wow. I'm glad I asked. And thanks for the explanation.

I think the service bulletin explained why it's ok to drive the PB port on the outlet block using the T output from the backhoe, but I didn't read it carefully enough to fully digest the info.

I have a BX23S, so I don't think the caution about the 3pt lever applies because there are three connections to the backhoe, so I'm assuming it has the full complement of ports.

That hoe has both PB and T ports because the pump is ion the back of the tractor and the hoe is the first valve in the circuit. It is feeding the loader and remotes in addition to the 3pt

Its still necessary to keep the lever in neutral. If not the 3pt valve will block the power beyond circuit and cause the pump to unload at relief pressure. Thst will also prevent the loader and remotes from working propetly.

Dan

 

[ejb11235]

That hoe has both PB and T ports because the pump is ion the back of the tractor and the hoe is the first valve in the circuit. It is feeding the loader and remotes in addition to the 3pt

Its still necessary to keep the lever in neutral. If not the 3pt valve will block the power beyond circuit and cause the pump to unload at relief pressure. Thst will also prevent the loader and remotes from working propetly.

Dan

Good point. Thanks. My specific interest in this is for eventually installing rear remotes for top 'n tilt. So other than curiosity, I want to have as good an understanding of valving and PB vs T as I can. Your explanations have been incredibly helpful.

 

[TheOldHokie]

Good point. Thanks. My specific interest in this is for eventually installing rear remotes for top 'n tilt. So other than curiosity, I want to have as good an understanding of valving and PB vs T as I can. Your explanations have been incredibly helpful.

If using a traditional valve you willbwant PB in addition to tank.

Dan