Go BottomAdding a BH With a Power Beyond Line
 | kfutavon
Join Date: Jul 2003 Posts: 5 Ona, WV 
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2003-05-07 54474
I have a Bolens G244 tractor with an FEL and am trying to figure out a way to make the backhoe I just aquired work on it. The backhoe is from A case 646B, it is a Davis D100 BH. I know almost nothing about hydraulics. The FEL has a seperate front mounted pump. It only has two connections, pump and return. The BH has a pump, return, and power beyond line. My question to anyone who can help is how can I set this up to work with my system? Thanks to all who can help.
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| TomG
Join Date: Feb 2002 Posts: 5406 Upper Ottawa Valley 
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2003-05-08 54495
There should be a bunch of reading in the archives about open-centered hydraulic systems. I'll save a bunch of words unless you can't find what you need there and I'll describe a possible connection. My assumptions are that the tractor has an open centered hydraulic system and that the loader's pressure and return lines are connected to a manifold block.
In open-centered systems, valve assemblies are connected to the high-pressure line in series. There are two assemblies in the case of a loader and 3ph, and the first valve assembly must be power-beyond rated to protect it against high-working pressures developed by the downstream valve. There are two basic ways of making a power-beyond rated valve assembly and it sounds like you've got one type on the loader and the other on the hoe. A power beyond valve that has only one return line has exhaust galleys heavy enough to withstand system pressures. A valve that has two return ports on its outlet section protects the exhaust galleys by diverting cylinder exhaust oil around the high-pressure line to return it directly to the sump.
The hoe valve is a type where the return port stamped 'PB' carries the open centre flow. It must be connected to the inlet port of another valve assembly, the return port on the manifold block or directly to the reservoir. The other port on the hoe valve often is called the low-pressure or TANK line, or is even called nothing at all. It goes directly to the sump. A plug ion the side of most tractor cases will accept a fitting for connecting a return line.
Whether the loader valve is power-beyond rated is an assumption. If you're certain it is, a common way to make a hoe connection is running the return line of the loader valve to the inlet line of the hoe valve and extend the loader's return line to connect with the hoe's PB line. The hoe's tank line still would have to go to the sump. It should not be connected with the PB line through a t-fitting. This type of connection is sometimes made using quick connector fittings so the hoe can be removed from the tractor. A short shunt line is used to connect the loader return line back to the manifold block. The hoe manufacture may have a way to eliminate the tank line in a power beyond application.
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| kfutavon
Join Date: Jul 2003 Posts: 5 Ona, WV
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2003-05-08 54534
Thanks for the great reply. It has helped me a lot. I don't think my loader valve has power beyond because the front pump only works the loader, and the loader has a seperate tank. The tractor 3pt is completely separate.
Would it work if I ran the high pressure line from the pump to the pump line on the BH, then run the power beyond line on the BH to the high pressure on the loader valve? If so, how would the return lines run from the BH valve and loader valve? Thanks again for all of the help. ....
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| TomG
Join Date: Feb 2002 Posts: 5406 Upper Ottawa Valley
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2003-05-10 54605
Sorry I missed your reply yesterday. I cut my netting short to do some other type netting related to the opening of Pike season here.
I missed that the loader has its own pump. A power-beyond rated valve isn't necessary in a system that has only one valve assembly, so it probably isn't PB rated assembly. In that case it should work to hook the hoe, which does have a PB rated assembly ahead of the loader. The hoe's low-pressure or tank line could be joined to the loader valve's return line provided that no component is between the t-fitting and the exit of the return line into the reservoir. High pressures can't be developed in the loader return line since it should have an open end to the reservoir.
A connection of the pump high-pressure line to hoe valve inlet (usually stamped P or IN) and the loader PB line to the loader IN port and the loader outlet to the reservoir should provide a path for the open-centre oil flow. You might want to consider quick-connector fittings if the hoe will be removed although I'd probably avoid them since the can pull apart fairly easily. There are some issues related to routing and securing hose.
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| kfutavon
Join Date: Jul 2003 Posts: 5 Ona, WV
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2003-05-14 54871
Thanks very much Tom! You have been extremely helpful. One last question, if you don't mind. The BH hydraulic lines are larger than the loader lines. Will this screw up the pressures to each? ....
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| TomG
Join Date: Feb 2002 Posts: 5406 Upper Ottawa Valley
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2003-05-15 54901
Different sized hoses are unlikely to change operation enough to be called a problem in itself. Could take some looking to find adapter fittings though.
The question does raise another issue. Different sized hoses may suggest that the implements are designed for quite different flow rates. A BH that is designed for a higher flow than the pump may be inappropriate for the tractor. There's are a bunch of discussions in the archives about hoes (and especially 3ph hoes) damaging tractors. A tractor that's small for a hoe also may run the hoe at unacceptably slow speeds or the system relief pressure may not be high enough to give it good digging power.
It would be good to ensure that the hoe is right for the tractor and the hydraulics are right for the hoe. Most manufacturers publish recommended flow and pressure ranges. Another problem that hoes sometimes produce is hot oil. Hoe work often is more intensive than loader work and oil can overheat. There's a rule of thumb that the reservoir should hold at least twice the pump's flow rate to allow oil to adequately dissipate heat. In this context, the small lines and valve throat would add to any heat problems.
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| kfutavon
Join Date: Jul 2003 Posts: 5 Ona, WV
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2003-05-15 54936
Thanks Tom. Looks like I've got a little bit of research to do before I pursue it further. ....
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