Remotes Spools - Power Beyond vs. Outlet?

[DiezNutz]

Hey Guys,

In the context of open-center Kubota implement loops, at least, I'm struggling to understand the subtle difference between

- PB port on a stack with PB
vs.
- Outlet port on a stack with NO PB (or PB plugged)

In each scenario, either port receives full flow of the Inlet port when all spools are neutral, right?
Aren't they both "cut off" from Inlet flow if one of the spools is diverting flow to a work port? (rendering the PB useless, really?)

I know the Outlet also gets "waste oil" from (e.g.,) the non-working port of a DA cylinder, but otherwise I don't see alot of difference.

I'm thinking no matter where I put the stack in the system, I don't really need a PB port... either just run the Outlet to my next set of valves or to the tank return.

Thanks in advance,
-DN

 

[KWentling]

If you're going to have any valve downstream of this valve it needs to be power beyond. The "out" on a regular valve is not designed to see pressure and should only go to the reservoir.

Kim

 

[BeezFun]

Hey Guys,

In the context of open-center Kubota implement loops, at least, I'm struggling to understand the subtle difference between

- PB port on a stack with PB
vs.
- Outlet port on a stack with NO PB (or PB plugged)

In each scenario, either port receives full flow of the Inlet port when all spools are neutral, right?

Not quite. There's no flow through the outlet port when in neutral, only the PB. When not in neutral there is flow through the outlet, but not the PB.

Aren't they both "cut off" from Inlet flow if one of the spools is diverting flow to a work port? (rendering the PB useless, really?)

The power beyond is cut off. That's why you can only run one implement at a time. The outlet has to be open, otherwise where would the waste oil go?

I know the Outlet also gets "waste oil" from (e.g.,) the non-working port of a DA cylinder, but otherwise I don't see alot of difference.

The oil that comes from an implement is displaced oil, it's only under enough pressure to be forced out of the cylinder.

I'm thinking no matter where I put the stack in the system, I don't really need a PB port... either just run the Outlet to my next set of valves or to the tank return.

I'd try to stop thinking that, it won't work.

 

[wdchyd]

I'm thinking no matter where I put the stack in the system, I don't really need a PB port... either just run the Outlet to my next set of valves or to the tank return.

Thanks in advance,
-DN

Do you think Manufacturers just make these PB valves for no reason at all....Think Again.....this topic has been beaten to death over and over for lots of good reasons!!!!!

You are only saying this cuz you don't understand hydraulic valve operation and design.....connecting valves in series without utilizing PB to drain relief valves to tank exposes unwanted overpressures in upstream components if multiple valves are being used at the same time.....possibly resulting in damaged hydraulic components and/or personal injury......:thumbdown:

Just do a search on "Power Beyond" to see for yourself......DON'T just connect them together w/o PB

 

[wdchyd]

Not quite. There is some kind of pressure reducing device in the valve, not sure if it's an orifice or what, but it causes the outlet pressure to drop to whatever the suction side of the system can handle.


The power beyond is cut off. That's why you can only run one implement at a time. The outlet has to be open, otherwise where would the waste oil go?


The oil that comes from an implement is displaced oil, it's only under enough pressure to be forced out of the cylinder.


I'd try to stop thinking that, it won't work.

What???????????:confused2:

 

[DiezNutz]

If you're going to have any valve downstream of this valve it needs to be power beyond. The "out" on a regular valve is not designed to see pressure and should only go to the reservoir.
Kim

Thanks Kim, this is a good point that hadn't occurred to me. I guess the Outlet-only type of valve assumes it's routing directly back to the tank.

Not quite. There's no flow through the outlet port when in neutral, only the PB. When not in neutral there is flow through the outlet, but not the PB.

I'm with you, but if you go back and read my original question, I'm talking about the subtle difference between 2 different valve setups... the 2nd kind has no PB port, therefore everything has to come out the Outlet port one way or another. Everything else you said (re: valve setup #1) I know/agree with.

Do you think Manufacturers just make these PB valves for no reason at all....Think Again.....this topic has been beaten to death over and over for lots of good reasons!!!!!

You are only saying this cuz you don't understand hydraulic valve operation and design.....connecting valves in series without utilizing PB to drain relief valves to tank exposes unwanted overpressures in upstream components if multiple valves are being used at the same time.....possibly resulting in damaged hydraulic components and/or personal injury......:thumbdown:

Just do a search on "Power Beyond" to see for yourself......DON'T just connect them together w/o PB

Hmmm, well first of all, welcome to TBN. You're on the fast track. :thumbsup:

Second, you try searching exactly for "power beyond" and then report back here what you come up with. Go on, try it. Or maybe it's that there's some advanced search capability that I don't know about, but the Search feature has always left alot to be desired IMO.

Third, I asked a specific question that I hadn't really seen asked, in the way that I asked it, in all the threads that I have read. I understand more about these valves than you're giving me credit for. But thanks for trying to help.


Anyway, I've got to think about this some more... because my existing return line doesn't really go directly to the tank, it goes to the PCV and 3PH cylinder. So no matter what, I *potentially* could have downstream pressure... so assuming I buy a stack with PB port and connect the PB port back into this "return", that leaves me with exactly where on the B3030 am I going to route this Outlet port to, to get directly back to the tank. (?)

 

[mmurphy]

I am having a hard time following here. If you are adding a set of valves, you need at least one set with PB. PB feeds to the added set(or old set). New valve, or old valve with out PB, yes has a outlet refered as T for tank or a return line. Or are you talking about an added valve that goes on a stack valve set up????
Wdchyd, does know what he is talking about. Read some of his posts in hydraulics, he has worked on a few systems.
The valves with out PB can not feed to another set for one reason is your pressure relief valve will not be able to relieve it self. At some point something might have to give if you are using valves that is being fed down stream.

 

[DiezNutz]

I am having a hard time following here. If you are adding a set of valves, you need at least one set with PB. PB feeds to the added set(or old set). New valve, or old valve with out PB, yes has a outlet refered as T for tank or a return line. Or are you talking about an added valve that goes on a stack valve set up????

The first one... adding a separate set of valves (for rear remotes).

The valves with out PB can not feed to another set for one reason is your pressure relief valve will not be able to relieve it self. At some point something might have to give if you are using valves that is being fed down stream.

I'm with you, but isn't it true that that's *only* a problem if you tried to use two different sets of valves simultaneously? Again, if my whole system is open-center, there isn't any pressure downstream if no downstream valves are being used - right?

Not trying to argue with anyone, it's just that there's lots of posts where everybody says "you have to use PB with separate outlet to tank", but nobody really completely explains why, and that's what I'm trying to understand. You guys are helping, thank you.

So what I've gathered from you and Kim is that even though such things as outlet-only open-center valve stacks exist, they're really only intended to be used by themselves or at the end of a run, where they can return directly to the tank with no back pressure. Right?

Maybe this will also help explain where I'm coming from/my confusion. My backhoe (set up by dealer) appears to be fed from the PB port of my loader valve. But there's only one line returning from it. I'm pretty sure that makes it an outlet-only. The BH manual says it should return to tank, so we can assume it is not designed to handle back pressure. BUT - It does not return to the tank, it returns to the hydraulic block, which as I pointed out earlier, goes to the PCV/3PH.

So naturally, my mind wonders "well if it's good enough for the BH, why isn't it good enough for a set of remotes?" I think the answer is, the dealer made the assumption (a reasonable one) that I would not be trying to use the BH and 3PH simultaneously, therefore the BH outlet will not see any downstream pressure (since it free-flows thru PCV).

I think the same logic could apply to remotes, only problem is I would definitely be using downstream PCV, and therein lies the problem.

Does that about sum it up?

I think I answered my own question about the return to tank, which is to tee into the loader valve return. Hence the "tee" everyone talks about (but seldom explains). I know, every tractor is different.

 

[rswyan]

See if this clears anything up for you:

On my B2910, my rear remotes are plumbed into the rear auxiliary hydraulic block (this is not the aux hydraulic source for the FEL, which is further forward)

The hydraulic source comes out of that rear hydraulic block via a line to the valve (3 spool Prince SV) - and then the power beyond off the valve runs back to rear aux hydraulic block - to operate the 3PH and position control valve.

The return line off the rear remote valve is plumbed (with a tee) into the same return that the FEL uses ..... (under the seat, near the cruise control linkage)

 

[mmurphy]

I'm with you, but isn't it true that that's *only* a problem if you tried to use two different sets of valves simultaneously? Again, if my whole system is open-center, there isn't any pressure downstream if no downstream valves are being used - right?

If you use down stream valves is the problem with the upstream valve....No pressure if no valves are actuated.

So what I've gathered from you and Kim is that even though such things as outlet-only open-center valve stacks exist, they're really only intended to be used by themselves or at the end of a run, where they can return directly to the tank with no back pressure. Right?

Correct.

Maybe this will also help explain where I'm coming from/my confusion. My backhoe (set up by dealer) appears to be fed from the PB port of my loader valve. But there's only one line returning from it. I'm pretty sure that makes it an outlet-only. The BH manual says it should return to tank, so we can assume it is not designed to handle back pressure. BUT - It does not return to the tank, it returns to the hydraulic block, which as I pointed out earlier, goes to the PCV/3PH.

I do not know what your set up is but, I bet you can not use 3ph when BH is on. Your system gets pressure relief back to valve with PB.