850 Power beyond: Loaders  -- Tractor Attachments Implements 3ph Discussion Forum and Review 850 Power beyond: Loaders -- Tractor Attachments Implements 3ph Discussion Forum

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 04-27-2002, 06:06 Post: 37883
steve Bogusta
2002-04-27 06:06:22
Post: 37883
 850 Power beyond

Can anyone tell me if I need this on my machine? I bought a Prince LVT Joystick two spool valve for my loader, on my 850. On the valve I am removing from machine, I have a PB port that's plumbed back to tractor. My new valve just has an IN, OUT, and four ports for the operations.There is a plug in new valve, Do I need it? What's Power beyond for? I just operate a 3 point and my loader... Thanks






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 04-27-2002, 07:05 Post: 37886
TomG

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 850 Power beyond

Humm! Seems like there should be some instructions along with the valve. Some valves can be used on either open or closed centre systems. Such valves come with a plug installed for use in closed centre systems. No guarantee, but that's probably the plug mentioned, and if it is, it must be removed for open cente use. I'm pretty sure that 850's are open centred.

Power beyond specifically refers to spooling control valve assemblies that have outlet sections with power beyond capability. They can be identified because their outlet sections have two return line ports. One port (often labeled TANK or T) carries cylinder exhaust oil, and the tank line normally goes directly to the TX/DIFF cases. The other line (often labelled PB) carries the open centre flow and normally connects to the auxiliary system return port on a manifold block. Exhaust oil is the oil on the passive side of a double acting cylinder that is displaced when the cylinder is operated.

The purpose of PB is to protect SCV assemblies in systems that have an additional SCVA or 3ph downstream. In open centred systems, operation of a control valve blocks the open centre flow, which allows high pressure to develop. The entire high-pressure line upstream from anoperated control valve, including any SCVA's, see the high pressure. For example, operation of the 3ph with a heavy load and a loader valve at the same time places system pressure on the exhaust galley portion of the SCVA. The exhaust galleys of many SCVA's are not designed for these pressures and can rupture.

Using a SCVA without power beyond in a PB application works if the valve is designed for the pressures or if it is never operated at the same time as a downstream valve that is carrying a heavy load.






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 04-27-2002, 19:34 Post: 37901
Mrwurm



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 850 Power beyond

Wow, TomG, you know alot about hydraulic systems. I have scoured my local libraries and online book stores for information on hydraulics and/or fluid power. I have never been able to find one. Certainly, there must be a book out there somewhere to teach us 'dummies' the basics about hydraulic systems.
Jerry






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 04-28-2002, 09:09 Post: 37908
DRankin



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 850 Power beyond

Tom, I see a book in the making. Should I save a spot in the "reading room" rack or wait for the movie version?






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 04-28-2002, 09:46 Post: 37909
TomG

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 850 Power beyond

Thanks for the comments. I also couldn't find basic material a few years ago. 'Let's Get Into Hydraulics' from Intertec Publishing is a collection of articles from the 70's and is mildly helpful. I found several textbooks in course outlines on the net, I didnít buy them because I couldn't tell how relevant they'd be from the tables of contents.

Mostly I've distilled comments from this and several antique tractor boards for awhile and added my own experience with minor problems. In particular, a mechanic named Bern who went on to teach at a community college and no longer posts often made very educational posts.

I'll probably keep looking for material myself. I've run across hydraulics stuff that isn't often found on compacts that I find interesting. Tandom open centre connections and indexing cylinders are examples.

I'm also much in the same state as everybody else. I can't find a good exploded diagram of a SCV assembly. Until mine stops working, I'll have little reason to take one apart. I never have the sense I actually know how something works until I've actually torn it down. Of course, I don't think I'll wish breakdowns on myself just to gain some practical experience.






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 04-28-2002, 19:26 Post: 37917
kenW
2002-04-28 00:00:00
Post: 37917
 850 Power beyond

The tank return port on my valve returns to my trans filling cap and is very easy to observe. In my hyd plumbing, the tank return does not always carry the cylinder exhaust oil but ALWAYS carries the oil vented by the hydraulic relief valve.






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 04-29-2002, 06:48 Post: 37928
TomG

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 850 Power beyond

Always a chance to learn something, and something I'm finding is that there virtually are never any universals with tractors.

Certainly pressure relief and safety valves would go into the tank line. Otherwise, a downstream valve could be closed and there would be no way to bleed off the high pressure. I guess it's possible, but I'd be surprised if most tank lines didn't carry oil whenever any cylinder connected to the SCVA moved. Oil on the other side of the moving piston has to go somewhere.

The problem with putting exhaust oil back into the PB line behind an operated valve is that the PB line may be blocked by an active downstream valve. In that case, the only way for the upstream cylinder to move is for the exhaust oil to move whatever load is on the downstream cylinder. The system pressure then would have to be enough to move both loads. However, such a hookup would work normally if only one valve at a time is operated.

I guess a test might be to operate two valves simultaneously and see if both cylinders move. That doesn't happen on my tractor. Operation of any valve on the loader SCVA stops movement of the 3ph and also cylinders connected to downstream valves on the same SCVA. I don't know how that could happen unless the cylinder exhaust oil goes into the tank line, unless the plumbing is a tandem connection, which I donít think is used on loaders. Of course, I always can be educated even if my wife doesnít think so.






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 04-29-2002, 12:57 Post: 37940
kenW
2002-04-29 00:00:00
Post: 37940
 850 Power beyond

That's exactly why I did test (observe) the system, all stemming from a comment the dealer made on delivery - "you can't operate the loader valve and the 3ph valve at the same time, but that's okay cuz most operators don't have both arms on the same side of their body."






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 04-29-2002, 20:53 Post: 37954
TomG

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 850 Power beyond

ken: I not sure from your description if you observed that thereís no flow in the tank line while loader cylinders moved, and at the same time observed that the 3ph stopped. If this is what happens then I'm not familiar with the hookup, but I'm curious. I also accept what you observed. I'm just trying to figure out how it might work.

If exhaust oil goes into a single return line (which is the case if a SCVA w/o PB is used) then operation of two valves at the same time in effect places them in series, and one cylinder cannot move without the other cylinder also moving. Thatís my understanding.

Exhaust oil flow is produced whenever a double acting cylinder moves because oil is on both sides of the piston. Without a tank line, exhaust oil must be carried by a single line, and that line may have additional valves downstream. Ordinarily exhaust oil would simply flow through any open centred downstream valves and on to the sump. However, if a downstream valve is operated, then the return line is blocked at that point. The only path for the exhaust oil is into a cylinder. Both cylinders would move until one reached its physical limit of travel.

My tractor uses a PB SCVA, and two cylinders will not move at the same time. There has to be return oil to the sump in an open centre system whenever a double acting cylinder moves. The tank line is the only other path I know of other than relief valves, so I have to think that oil is flowing in the tank line rather than the PB line whenever my loader is active.

There is a hookup called an open centre tandom connection where cylinders can sort of move simultaneously. The cylinders in effect are plumbed in parallel rather than series. In a tandom hook up, single cylinders will move when their valves are operated. If two valves are operated, both cylinders can move, but the cylinder with the lightest load moves first until its limit of travel is reached. Tandom plumbing could be an explanation, but I'm not aware of its use on tractor loaders.

I understand the delivery guyís joke. However, I did bump my 3ph into lift once when the 3ph was locked down by a backhoe mountóan arm and a leg can do it.






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 04-30-2002, 17:19 Post: 37977
kenW
2002-04-30 00:00:00
Post: 37977
 850 Power beyond

TomG - I observed the return tank flow for the loader only functions. The advice was to not operate loader & 3ph at the same time so I didn't but I can visualize arm/leg accidentals.

My loader double valve operates as you describe as parallel tandem. I have a '94 Kubota B7100 sold in Canada with loader LA300B and guessing from discussions on the other tractor board, was not a combo available in USA so I'm not sure why the valve is what it is or why it is plumbed the way it is.






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Discussion Boards > Active Subjects > Messages as Posted > Loaders Forum

Thread 37883 Filter by Poster:
DRankin 1 | kenW 3 | Mrwurm 1 | steve Bogusta 1 | TomG 5 |




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