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...

 

[CJONE]

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.

Yes that keeps pumps from exploding. Or just plumb it correctly with the right parts. I am on my 21st year of doing this for a living and had to add a separate relief 2 times in a open system. Both times were a small tractor that used the return flow for steering. A small priority flow divider is what I normally use but getting people to spend the extra few dollars is next to impossible sometimes. A multi circuit pump is the best option but again the almighty dollar wins out in a lot of cases. CJ

 

[BukitCase]

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

Think about this for a minute - since nearly ALL this type valve can only withstand up to 500psi on the return gallery, and since anything DOWNSTREAM of a (properly operating) RELIEF valve can NOT get higher than what that relief valve is set at,

How much power can you get using 500 psi in a system that wants at least 2000 psi???

Not tryin' to pick on anybody here, just trying to keep anybody from rushing out and paying for something they don't need, won't work, doesn't fit where they want it, etc - BTDT, don't see a need for others to find out the hard way too... Steve

 

[CJONE]

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

Think about this for a minute - since nearly ALL this type valve can only withstand up to 500psi on the return gallery, and since anything DOWNSTREAM of a (properly operating) RELIEF valve can NOT get higher than what that relief valve is set at,

How much power can you get using 500 psi in a system that wants at least 2000 psi???

Not tryin' to pick on anybody here, just trying to keep anybody from rushing out and paying for something they don't need, won't work, doesn't fit where they want it, etc - BTDT, don't see a need for others to find out the hard way too... Steve

When you hook the return from your primary valve with out PB with the system relief up to a secondary valve you eliminate the relief path in the primary valve. No relief = either a junk pump or valve bank when both units are used at the same time. CJ

 

[BukitCase]

Did I misunderstand this part - "running a system relief ahead of them all with it's own tank return."

So why would a SEPARATE RELIEF that is AHEAD of EVERYTHING, NOT limit ALL system pressure to whatever that FIRST IN LINE relief is SET for?

 

[J_J]

I think the OP understands the purpose of PB, but here are some other points.

The PB port can be used as a return port as the galleries are connected in the basic valve.

Some valves are made without PB port and are to be used as the last valve in a hyd system. Example is, most log splitter valves. Log splitter tank port should go to tank.

The PB port is only PB when the adapter is installed, and the purpose is to separate the galleries into a tank port and the Power Beyond.

With adapter installed, any fluid not used by the cyl ports is routed through the PB port.

All used cyl fluid is routed to the tank port as low pressure.

With all valves in neutral, pump flow through all valves is low pressure.

There must be a relief valve between the pump and first valve in an open center hyd system.

PB is just that, Power Beyond that valve, feeding the next valve or to tank.

The last valve in a hyd system does not need PB.

 

[muddstopper]

Did I misunderstand this part - "running a system relief ahead of them all with it's own tank return."

So why would a SEPARATE RELIEF that is AHEAD of EVERYTHING, NOT limit ALL system pressure to whatever that FIRST IN LINE relief is SET for?

Most of the valves have a built in relief. Connecting another valve downstream of the first valve without a power beyond port doesnt not give the relief anywhere to dump overpressure oil back to tank as all oil flow must go thru the tank port and in this situation, the second valve would have to handle the relief flow as pressure in the IN port of second valve. since the relief valve of the second valve is after the first valve, the tank port would be subjected to whatever pressure the second valve is set at. You can add another relief before the first control valve to let excess pressure bypass back to tank before the first control valve, but you would still be subjecting the out port of the first valve to what eve the pressure setting is of that relief. adding a seperate releif ahead of the system is an unnecessary expense that still wont provide protection for the low pressure only tank port of the first control valve.

 

[Trials]

"POWER BEYOND (Also referred to as high-pressure carryover), obtained by using a sleeved outlet that carries oil under
pressure directly from the open center passageway of a control valve to the inlet of a down-stream control valve bank. This sleeve outlet prevents back pressure on the exhaust or return passage of a control valve which normally is not designed to take high pressure.
This option also prevents back pressure on spool seals and also does not put back pressure on the built-in relief valve which, if allowed, tends to increase the relief valve opening point to the total of the relief valve original setting by the amount of back pressure in the control valve exhaust passage. This option is often used to obtain more valve sections or spools than normally obtainable by one control valve bank, or used when additional spools need to be added in the field. Still another use is to obtain a circuit in which it is desirable to have certain valve functions take priority on flow. This is accomplished by having those functions requiring priority flow be controlled by the upstream valve bank equipped with power beyond, then whenever a spool of the power beyond valve is fully activated, this will take all oil from pump and stop the flow of oil to any downstream valve until the power beyond valve spool is returned to neutral, at which time oil will again flow to the downstream valves. NOTE: It is always necessary to provide a tank return port on all power beyond valves in order that the return or sump oil from a cylinder or motor can be returned to the tank.

When several valves are fitted in a power beyond hook-up, it is also possible to provide different relief valve settings for each
bank of valves in the circuit provided the highest pressure is in the valve bank closest to the pump and the next highest in the second bank, etc. If all valve spool functions are to operate at same pressure, then only the first valve bank needs to be equipped with a relief valve and all downstream valve banks do not need a relief valve, however if they are equipped, the reliefs in all valve banks should have the same setting."

http://www.baumhydraulics.com/files/infobuild/terms_hydraulic_control_valve.pdf

:detective: you'll have much better luck if you google entire terms instead of obscure acronyms.

 

[ch1ch2]

Now I understand.

Thanks to everyone!!!!!

 

[CJONE]

:thumbsup:

Now I understand.

Thanks to everyone!!!!!