How does hydraulics (& PowerBeyond) work?

[CobyRupert]

Deere 5057E w/ 553 loader.

I need a new hydraulic hose to my loader control valve. I want to understand why there’s 3 hoses from the tractor (from the end of the stacked SCV’s) to the loader control valve. Deere, in the manual, calls them: B)Excess Oil Return Line, C) Oil Return Line, and D) Oil Supply Line

Hose “C” (“Oil Return”) is the hose I need to replace. Its port on the loader control valve is labeled “PB” (Power Beyond?). Does this makes sense?

What I also don’t understand: Hose “D (Oil Supply Line)” connects at the loader valve port labeled “T”. Isn’t “T” suppose to be the port on a valve that is piped to the Tank?

Why 2 return lines? What is the difference between “B Excess oil return” and “C Oil return”?

 

[TractorTech]

Oil return aka PB takes oil from the loader valve and sends it down the line for other hydraulic functions to use such as rear remotes or the 3 pt.
Excess oil return is takes oil that is exhausted from the loader cylinders and returns it to the sump under no pressure.
Oil supply line is incoming pressure from the pump. Not sure why the port is labeled "T"

 

[rScotty]

I agree with Tractor Tech. Below is some more detail. And I also don't know why you have a port labeled in the manual as an oil supply line that is labeled "T". My guess is that someone wrote it up wrong in the manual. Surely the valve manufacturer knows what his ports do. And as you say, "T" is tank return on every SCV I've ever seen.

I'd be tempted to trace the hoses and try to make sense of it. But do you really need to do that? You know you have to replace a particular hose, and it sounds like you know it needs to be a hose rated for your system pressure.

HERE'S SOME MORE DETAIL:
All selective control valves aka SCV or the "loader control valve" have two or three fluid circulation ports - we are not counting the additional feeds to the loader cylinders.
Traditional nomenclature for All SCVs is to have an IN or P port from the high pressure pump, and also a port labeled OUT or T or sometimes RETurn to circulate unused fluid back to the sump tank.

Some SCVs also have a third fluid port called the Power Beyond port labeled BYD or similar which can be configured with internal sleeves to be either as an additional return line, or as a full pressure port to provide pressurized fluid to the IN port on another valve stack - often rear outlets.
Luck,
rScotty

 

[CobyRupert]

Thanks for the info.

The “PB” port as a PowerBeyond (“Oil Return”) makes sense. And hose is under pressure.

The loader control valve is a: Sauer Danfoss RE179201. I can’t see what the port on the back side of mine is labeled, but I found a picture of my style, and it shows a “P” for the back side port.

My manual says that the line to the P port is an “Excess Oil Return” line. Like the “T” port being used for what manual says is an “Oil Supply” , this also seems backwards. Yes?

I’m starting to think the manual is off. Or maybe the dealer piped the loader valves “T” and “P” ports backwards? … Would that matter? It hasn’t so far.

…but the port to port connections (however labeled/mislabeled) from the tractor to the loader valve are connected like the manual shows. And everything works.

Hmm..if I only knew what each ports on the tractor did. Then I’d know if the valve is piped backwards, or if the manual mislabels the function.

 

[rScotty]

Thanks for the info.

The “PB” port as a PowerBeyond (“Oil Return”) makes sense. And hose is under pressure.

The loader control valve is a: Sauer Danfoss RE179201. I can’t see what the port on the back side of mine is labeled, but I found a picture of my style, and it shows a “P” for the back side port.

My manual says that the line to the P port is an “Excess Oil Return” line. Like the “T” port being used for what manual says is an “Oil Supply” , this also seems backwards. Yes?

View attachment 1673709

I’m starting to think the manual is off. Or maybe the dealer piped the loader valves “T” and “P” ports backwards? … Would that matter? It hasn’t so far.

…but the port to port connections (however labeled/mislabeled) from the tractor to the loader valve are connected like the manual shows. And everything works.

Hmm..if I only knew what each ports on the tractor did. Then I’d know if the valve is piped backwards, or if the manual mislabels the function.

You ask, 'Could it work if the "T" and "P" ports were connected backwards...? '

Well, that's a fascinating question. Loader control valves are of a type called "spool valves". Your JD 5075E tractor uses a hydraulic system called "open center" type. And as you guessed, the simplest type of SINGLE SPOOL control valve in that type of open center system will theoretically will operate with the P and T ports reversed. The spool valve just slides back and forth allowing the lands and cutaways on the spool to connect ports so that fluid can flow. Those simplest spool valves work without any spring-loaded poppet valves inside that would only operate one way.

Would a DUAL SPOOL control valve operate with input and output like that? Again, the simplest type would....it's just two singles in parallel. But yours isn't that simple. From your photo, yours \also has a relief valve & a float position. Plus I would be surprised if your loader plumbing doesn't also allow for limited regenerative flow in each hydraulic cylinder. So without a cutaway view of the SCV I don't know. My guess is it might work somewhat with the P and T ports connected in reverse, but not as well or as fast as it should.

JD is very sophisticated with their hydraulics. But that model was not US made, it was made overseas so maybe there are some translation errors. See if you can find a cutaway view of that SCV and go from there.

Also, I did look around on Google to see if I could find a good pictorial view of a SCV - which is also known as a DSV or "Directional Control Valve...same exact thing. I didn't find what I wanted, but did find this excellent short article. It is only a single spool type DCV, but it works the same.

Intro to Directional Control Valves

Learn about Directional Control Valves with this Hydraulics Lesson. LunchBox Sessions is a new take on online industrial training, full of interactivity, used by individuals, schools, and companies around the world.

www.lunchboxsessions.com

Luck, rScotty

 

[CobyRupert]

Basically the loader valve has 2 SCV valves: I and II. Each SCV has a port A & B. Valve I for the loader boom has a float mode (beyond retracting/lowering/ pressurizing port IA), Valve II has a regenative mode (beyond extending/dumping/ pressurizing port IIA). Both extra modes appear to work.

My understanding is both of those extra valve modes create a “shortcut“ path for oil to pass between the rod and head side of the piston? (Effect: The boom floats, and the bucket dumps faster.)

Now I just need to track down what the Power Beyond ports are on the end of the rear SCV spool valves… holy smokes…typing this made me remember I added the second rear SCV spool myself years ago …maybe I still have the instructions. Maybe they have those details.

 

[rScotty]

Basically the loader valve has 2 SCV valves: I and II. Each SCV has a port A & B. Valve I for the loader boom has a float mode (beyond retracting/lowering/ pressurizing port IA), Valve II has a regenative mode (beyond extending/dumping/ pressurizing port IIA). Both extra modes appear to work.

My understanding is both of those extra valve modes create a “shortcut“ path for oil to pass between the rod and head side of the piston? (Effect: The boom floats, and the bucket dumps faster.)

Yes, that is right. Seems like you have a good sense of how both the "passive regeneration" and the float functions work.

Now I just need to track down what the Power Beyond ports are on the end of the rear SCV spool valves… holy smokes…typing this made me remember I added the second rear SCV spool myself years ago …maybe I still have the instructions. Maybe they have those details.

If you did that addition, do you remember putting the special Power Beyond sleeve into the upstream PB port? That sleeve was necessary for the PB port to develop pressure. Then using that sleeve and pressurized PB port makes it possible to daisy chain several SCVs together - using each PB to feed the IN port of the next SCV.

But each SCV in the series must also have its Return/OUT port plumbed. All the return lines from all the SCV can be Y'd together, but the total return hose diameter must be large enogh to avoid any back pressure on the return ports.

 

[CalG]

Port and power beyond are pressurized.

Return and Tank should see no pressure other than pipe friction.

A leaky valve, without a way to drain, will see line pressure build in the valve body in places where pressure is not intended. A relief return is required!

If mechanicals were perfect, the third line to tank would not be needed.

Guess what?....

Valves are NOT perfect.

 

[CobyRupert]

I’m trying to figure out the function of the ports at the power beyond block at my tractor. (I.e. does my manuals have typo, or is the loader valve “T” and “P” ports piped “backwards”?).

Here’s a “similar” photo from a manual that is years newer than my manual. Can you tell flow direction from the descriptions?

It shows the EXACT SAME port-to-port connections as my manual shows (and tractor has), between the tractor and the loader valve. Loader operates fine.

….but they have different descriptions…and it’s hard to tell which end of the hose the “inlet” or “outlet” refers to.

“B” line to the loader valve port “T”: Picture call this “B - PBP port: power beyond to mid-SCV” (My manual tagged this as: D line- Oil supply hose)

“D” line to the loader valve port “P”: Picture calls this “D- Inlet port of power beyond to mid-SCV” (My manual tagged this as: “B line - Excess Oil Return”)

“C” line to the loader valve port “PB”: Picture calls this “C- Outlet port: power beyond to mid-SCV” (My manual calls this “C - Oil Return)

In both cases, does it sound like the valve’s “T” port is receiving pressurized oil supply?

 

[rScotty]

Sounds to me like the guy writing the manual didn't understand hydraulic systems. You might check to see if your shop manual has a flow diagram.
That may help.