HYDRAULIC HOW TO

[CIRCUIT BREAKER]

I am building a backhoe attachment for my tractor. I am ready to tap into my hyd's. My tractor has a front end loader, but does not have power beyond. The loader has quick disconnect fittings. My new 6 spool control also does not have power beyond. My question will it work if I take the" return" from one and hook it up to the" in" on the other, and then the return to return. Will this work? In other words hook them up in series. All controls are open center. I have a L2850 Kubota. Thanks for your help.
Wayne

 

[oldnslo]

No you cannot pressurize the tank line on most valves. Possibly check to see if power beyond is an option for L2850. I suspect it is but I am not familiar with that model Bota.

 

[teg]

...but does not have power beyond...

What makes you think this? I'm pretty sure your L2850 has power beyond... it's open center. Does it have a kubota loader or an aftermarket one (still think it should have PB)? What valve did you use for the backhoe? Do you have the model number of the backhoe valve?

 

[CIRCUIT BREAKER]

What makes you think this? I'm pretty sure your L2850 has power beyond... it's open center. Does it have a kubota loader or an aftermarket one (still think it should have PB)? What valve did you use for the backhoe? Do you have the model number of the backhoe valve?

Thanks for the reply. I am not wanting to put pressure to the tank. Pressure in to the loader valve, out of loader valve into pressure side of backhoe valves, out of backhoe valve into tank. ( not really tank, but trans) Will this work? All valves open center. No this is a after market loader. Bush Hog brand. I know the tractor has power beyond but this is what is feeding the loader. Pump feeding a block mounted below the pump, out of the block line feeding 3 point lift,line feeding loader. All ports used up. Would be perfect if I could use pressure line feeding 3 point lift but this is factory hard line with special ends and would be hard to deal with. Sorry I do not remember what brand of valve I bought but it is a 6 spool open center. I have not hooked lines to the backhoe yet, I am still working on it. I am building it so I can remove when not needed as I use this tractor for other things. The loader valve has a large plug(#12 SAE 1 1/16" O ring) this port is labeled P B. It has no brand name on it. I do not think you can just screw in a fitting and feed my backhoe valve. I think you would have to do something to use the power beyond port (sleeve, ect.) but no idea what.Thanks for your help!

 

[teg]

First, I have a friend with L2850 and a bush hog brand loader... I can look at his (only problem it's 3 hours away). I don't know for sure since I don't know what valves you have but you should have 3 lines going to your loader. One is High pressure IN and one line (PB) high pressure OUT, the third one is Low pressure return to the tank/transmission. I plumbed a 3 valve spool (yours is 6) after the FEL but before the 3ph.

...Pressure in to the loader valve, out of loader valve into pressure side of backhoe valves, out of backhoe valve into tank. Will this work?

NO, you have to feed the 3ph. Power goes from one thing to the next with everything connected in a line (in series).

...I know the tractor has power beyond but this is what is feeding the loader. Pump feeding a block mounted below the pump, out of the block line feeding 3 point lift,line feeding loader. All ports used up.

Fluid (power) goes from the Pump to FEL, then the 3PH. It does not feed both at the same time (that would be a Closed System).

Would be perfect if I could use pressure line feeding 3 point lift but this is factory hard line with special ends and would be hard to deal with.

Use the power out (PB) from the FEL to feed the spool, return the power beyond from the spool to where the FEL had gone before (so it can feed the 3ph). You have to have a low pressure return to the tank from your backhoe 6 spool. This is the only line you can "T" into. I "T" into the FEL Low pressure return line with mine.

Sorry I do not remember what brand of valve I bought but it is a 6 spool open center.

Can you post a photo of it? IF you don't know how to post a photo, let us know and we can show you).

The loader valve....port is labeled P B....I do not think you can just screw in a fitting and feed my backhoe valve.

Actually it's not THAT simple (you need a low pressure return line, too) but basically, Yes you can do that.

I think you would have to do something to use the power beyond port (sleeve, ect.) but no idea what...

The PB port on your FEL is actually already powering your 3ph in series (one after another). To test it, run the tractor while you are raising the 3ph, lift your bucket up at the same time and your 3ph will lose it's "power" because the FEL is using all of it.

{edit} I will find a photo that might help you but it's for another tractor... Mine.

 

[CIRCUIT BREAKER]

First, I have a friend with L2850 and a bush hog brand loader... I can look at his (only problem it's 3 hours away). I don't know for sure since I don't know what valves you have but you should have 3 lines going to your loader. One is High pressure IN and one line (PB) high pressure OUT, the third one is Low pressure return to the tank/transmission. I plumbed a 3 valve spool (yours is 6) after the FEL but before the 3ph.

NO, you have to feed the 3ph. Power goes from one thing to the next with everything connected in a line (in series).

Fluid (power) goes from the Pump to FEL, then the 3PH. It does not feed both at the same time (that would be a Closed System).

Use the power out (PB) from the FEL to feed the spool, return the power beyond from the spool to where the FEL had gone before (so it can feed the 3ph). You have to have a low pressure return to the tank from your backhoe 6 spool. This is the only line you can "T" into. I "T" into the FEL Low pressure return line with mine.

Can you post a photo of it? IF you don't know how to post a photo, let us know and we can show you).

Actually it's not THAT simple (you need a low pressure return line, too) but basically, Yes you can do that.

The PB port on your FEL is actually already powering your 3ph in series (one after another). To test it, run the tractor while you are raising the 3ph, lift your bucket up at the same time and your 3ph will lose it's "power" because the FEL is using all of it.

Thanks for reply. Loader has 2 lines. In and Out, other 4 lines to hyd. cyl. Out of the end of block below the pump 3 hard lines going to 3PH. Can you just screw a fitting into the PB port of the loader valve to supply the backhoe valve, after removing the plug? I know the out of the backhoe valve goes to the tank. I removed the PB plug and rigged a hose. Started the tractor. Fluid flowed from the port. The loader worked the same. The fluid flowing from the port would decrease when loader under heavy load, all other times flowed like crazy. Thanks for your help!
Wayne

 

[aczlan]

Yes, however you may need a "power beyond" plug so that you don't send high pressure fluid into the tank port. Can you post some clear closeup pictures of your loader valve including any tags or cast in numbers?

Thanks

Aaron Z

 

[CIRCUIT BREAKER]

Thanks for your help. I think I am starting to see the light. I bought a HP gauge, removed the large plug on the FEL marked P B. It had no pressure. As soon as I can I will remove the quick disconnect feeding the FEL, order new hoses. Run a line line from there to the P in on my backhoe. Out of my backhoe, to the line I disconnected feeding the FEL. I am not doing anything with the return (out) from the FEL valves. Should work? Thanks again, I did not want you to think I stopped working on it. I am working on it every chance I get. I will keep you posted. As soon as I get the hyd's worked out I am going to remove the backhoe, dissemble,complete all welding,prep,prime and paint, then start using!

 

[Jay4200]

Thanks for reply. Loader has 2 lines. In and Out, other 4 lines to hyd. cyl. Out of the end of block below the pump 3 hard lines going to 3PH. Can you just screw a fitting into the PB port of the loader valve to supply the backhoe valve, after removing the plug? I know the out of the backhoe valve goes to the tank. I removed the PB plug and rigged a hose. Started the tractor. Fluid flowed from the port. The loader worked the same. The fluid flowing from the port would decrease when loader under heavy load, all other times flowed like crazy. Thanks for your help!
Wayne

Does your 3pt hitch work? If it does, your loader has power beyond. The hydraulic block diverts flow out of the block to all accessories in series, then back to the block, which then runs the 3pt - 3pt is last in line. There is also a sump input on the block for non-PB returns. The line that goes back into the tractor from the loader IS power beyond - port PB, and that is the line that must run back to your backhoe (unless your 3pt is currently disabled). The PB return from the backhoe will then go to the block to run the 3pt. You'll have to add a 'T' for the return to sump for both the loader and backhoe. My backhoe setup is mounted on a subframe, and it has a two-line hydraulics with no PB - my backhoe exhaust goes to sump with nothing returning to drive the 3pt; my 3pt is disabled while the backhoe is connected. That is also an option, unless you have a 3pt mount and you need the 3pt to operate.

 

[100 td]

Please correct me if I'm wrong
In a open center system, you can add another open center valve at ANY point in the series circuit after the pump, including the return to tank line if it is a high pressure line, or directly after the 3P HITCH before the return line. If you can't, please explain why?
TANK-----PUMP--[Optional]--FEL--[Optional]--3P HITCH--[Optional if HP line]---TANK

 

[teg]

including the return to tank line if it is a high pressure line,...

The return line is not high pressure and doesn't have oil flowing all the time though it... also, don't know where (or if) you can tap in *after* the 3ph, might be all internal plumbing after the hitch.

 

[LD1]

Most tractors cannot be tapped after the 3PH. The 3PH is the last in line, there is no PB off the 3PH, and the return is all internal.

You can tap in before the loader, or after the loader on most tractors. Thats about it.

It seems to me you dont have a good grasp on just what PB is, so I'll try my hand at explaining.

PB is also sometimes called carry-over, or high pressure carry over. And I have seen it marked as PB, PBY, Y, or W on different valves. All basically mean the same thing.

Now, about how it works.

The tank port on most valves is designed to have 400PSI or less. Just not meant to have pressure on it, and you dont want back pressure on it. It can cause some weird things if you ever tried to use two valves at the same time.

On a normal, non PB valve, there is only 1 place for fluid to come in (P), and one place for it to leave (T). Then ofcourse your two work ports (A and B).

On a PB valve, There is an additional port. You still have only 1 inlet (P) port, but now have a PB and a T port for fluid to leave. while the valve is in neutral, fluid comes in the P port, and exits the PB port and on to feed the next valve in the series. Whenever you use that valve, It opens the work ports, one to P and one to T. That way you arent sending the return fluid coming out of a cylinder downstream to the next valve....rather you give it a direct return to tank.

When you try to send return oil downstream to a next valve, and are trying to use that next valve at the same time, is when some weird things can happen. You have the ability to over-pressurize things downstream, or lack pressure to do anything and could cause a load to drop.

I am betting your loader valve DOES have PB. as that is likely how the 3PH is fed. You new valve also NEEDS to have PB, that way you can still feed the 3PH. IF your new valve doesnt have PB, you need to see if it is an option and all you need is a $20 plug to install in it. If it is not PB capable, you cannot use that valve.

Here is how it needs to be plumbed.

 

[dfkrug]

Here is how it needs to be plumbed.
View attachment 475125

Note that the backhoes you buy to attach to compact tractors "never" have PB on their
valves. I say "never" carefully. I have seen and owned many hoes, and I have not run
into one yet. Not talking industrial hoes here.

That said, you can get away with the config in your picture since you can not really use
the 3-pt when the hoe is attached. Therefore, you can't really over-pressurize the OUT
port of the hoe's valve. So you are really just using the 3-pt valve IN port as a Tank
port for the hoe when it is attached.

Since the OP wants to build his own hoe, he can buy a 6-spool hoe valve with a PB
out, but that will cost more, and require 3 hoses instead of 2. When I built my CADDigger,
I used a Prince stack valve without PB, and noted that PB was an option.