Please explain PB

[MossRoad]

Thanks a bunch Moss.

I forget who originally posted that link to the army FM here on TBN, but it was a long time ago and I am eternally grateful. Every time I get confused on hydraulics, and JJ is getting inclined to drive up here and smack me around, I pull out that link, start reading, and go back to school.

 

[joefromga]

Let me take a shot at it, maybe I can help...

Awesome explanation.

What happens if you T the pressure line to another spooler? Could it be used like a PB or would you lose pressure when the original valve is used in the other direction?

 

[MossRoad]

I think if you TEE the pressure line to two valves, the one with the least resistance will get the full flow. Maybe a flow divider would be used instead of a TEE?

 

[stuckmotor]

I do not see any that would fall under the topic of Hydraulics.

PB = Power Beyond

The abbreviations used here and nearly everywere else usually drive me crazy. For some reason I got this one straight off, go figure.

 

[Tx Jim]

Awesome explanation.

What happens if you T the pressure line to another spooler? Could it be used like a PB or would you lose pressure when the original valve is used in the other direction?

Teeing a control valve into an open center hyd system will not operate properly. As previously stated oil will take the path of least resistance. Valve must be attached in series not in parallel. On the other hand one can tee a control valve into a closed center system.

 

[ch1ch2]

Yes MossRoad, That makes sense. I think. But wouldn't the same thing happen if the steering valve were the first valve in a series?
I know two of my tractors have flow dividers at the pump so the steering always gets what it needs. Don't know where the brakes get their hydraulics.

I don't know why I am having such a hard time understanding this.

I have a picture diagram from a local shop that shows oil leaking from the first valve when NOT using PB. So I am thinking it is like muddstopper said (post 14). It has something to do with back pressure.
Maybe that is why I have a hard time understanding it. Why would back pressure be an issue? To me back pressure would not stop at the return port of the first valve but would be on the entire line back to the pump and the relief valve would release the back pressure before damage to the first valve.
Why would manufactures design a weakness into the valve at the return port just to have to design a separate correction? I would think that manufacturers put on more PB's at the time of manufacture than they would sell in after market.

Maybe I should just accept that it is a safety type device and move on. If I did that, it would mean I have to rely on the dealer to fix my tractors if I want to add hydraulic valves. And I do want to add valves to 3 tractors.

 

[ch1ch2]

I will be away from the computer for a few days so don't think I abandoned this tread.

 

[CJONE]

Yes MossRoad, That makes sense. I think. But wouldn't the same thing happen if the steering valve were the first valve in a series?
I know two of my tractors have flow dividers at the pump so the steering always gets what it needs. Don't know where the brakes get their hydraulics.

I don't know why I am having such a hard time understanding this.

I have a picture diagram from a local shop that shows oil leaking from the first valve when NOT using PB. So I am thinking it is like muddstopper said (post 14). It has something to do with back pressure.
Maybe that is why I have a hard time understanding it. Why would back pressure be an issue? To me back pressure would not stop at the return port of the first valve but would be on the entire line back to the pump and the relief valve would release the back pressure before damage to the first valve.
Why would manufactures design a weakness into the valve at the return port just to have to design a separate correction? I would think that manufacturers put on more PB's at the time of manufacture than they would sell in after market.

Maybe I should just accept that it is a safety type device and move on. If I did that, it would mean I have to rely on the dealer to fix my tractors if I want to add hydraulic valves. And I do want to add valves to 3 tractors.

Picture a valve as having 2 passages in the main body. one passage [core] is for pressure, one passage [core] is for return oil. In a non power beyond valve both cores are combined in the valve just before the outlet, remember a return core can only handle a few hundred pounds of pressure. In a PB valve both cores are accessible on the outside of the valve. One HAS to go to tank and the other core goes to another valve or pressure requirement. If your valve has a pressure relief and almost all of the first valves in line do, that has to relieve to tank. So if you hook the return from a non power beyond valve to another valve, how does it relieve? It doesn't I have seen pump shafts broken, housing broken and many many valve blocks cracked and seals blown out of retainer plates. There are a few valves out there that will handle backpressure on the return core but very few. Hope this helps. CJ

 

[GLyford]

You could try to prevent that by running a system relief ahead of them all with it's own tank return.

But I think the other thing that could help the OP here is that the factory valve does not HAVE to be the first valve in the system. If he buys PB valves for his 3 tractors, and diverts the supply from the factory valves to go instead to the new valves, and goes from the PB ports back to the factory valves' inputs then he is where he wants to be, and without having to replace the factory valves.

 

[MossRoad]

You could try to prevent that by running a system relief ahead of them all with it's own tank return.

But I think the other thing that could help the OP here is that the factory valve does not HAVE to be the first valve in the system. If he buys PB valves for his 3 tractors, and diverts the supply from the factory valves to go instead to the new valves, and goes from the PB ports back to the factory valves' inputs then he is where he wants to be, and without having to replace the factory valves.

Yep. He can put add-on valve ahead of his current valves, and feed the current valves from the power beyond port on the add-on valve. Just have to remember that first valve in line has priority over second valve, over third valve, over factory valve, etc...