hydraulic systems

[htiek126]

How do hydraulic systems without power beyond (closed center system) work? I am plumbing my 1510D for a FEL with a power beyond valve. I have since spotted a small inexpensive Bradco hoe for sale. It only has two hydraulic connection hoses, so I am expecting it is a closed center system. Can I plumb in some sort of relief valve upstream of the back hoe, or do I need to get an open center valve system for the hoe (very expensive!)?

Keith

 

[EdKing]

Just because the hoe only has 2 hoses doesn't mean its closed center. My backhoe has 2 hoses that connect to one of my SCVs, and it is open center. The control valves divert the oil to the cylinder that is operating, and when let go the oil flows through to the tractor. I am assuming that most if not all tractors operate with open center, so if the hoe is designed to operate on a tractor, it is open center.

 

[bruce1966us]

I agree, most 2 line systems are open center. Very simple to deal with. Every loader we install is open center.

Thanks,
Bruce
www.yanmartractors.com

 

[lens12]

An open center system uses a pump that pumps a constant volumn at a specified rpm. A closed center system varies the volumn according to the hydraulic demand. Most newer farm tractors use closed center systems. If you use a closed center valve on an open system the pump flow will be deadended & wreck the pump. If a open center valve is used on a closed system, the pump will pump at full capacity & the oil will overheat.
A valve with power beyond has 3 hoses . When the valve isn't being activated oil flows in the IN & out the PBY to another valve , such as the 3 point. When the valve is activated the oil goes through the valve to the application with the return from the application going out the OUT port to the hydraulic reservour. . A valve can be operated without the PBY fitting. The oil will go out the OUT to another application(may be back pressure, this is why PBY is used) or to the reservour

 

[bruce1966us]

Len just proved the point I was making. Open center is more simple.

Thanks,
Bruce

 

[htiek126]

I want to make sure I understand... You are saying that a two hose valve can have an open center system by combining the power beyond and out lines. The back pressure would then be caused by the use of a valve down stream and/or is the back pressure caused by a spool that is partially open?

 

[DFB]

Maybe these diagrams can help out. Both open and closed center systems are described and shown with and without power beyond.

http://www.bareco.com.au/files/hydraul/hydraul2001/hy17.htm

DFB

 

[roger_scotty]

Keith, you are doing the right thing in plumbing your 1510D for an open center with PB. Stay the course! A multiple spool valve with PB will give you all the options and is the simple, cheapest, and best way. Your can daisy chain other valves in series with the PB port on a PB-type valve. BTW, the backhoe will work with any system that provides hydraulic flow.
What Len is saying that there is a way to use a single set of non-PB spool valves - (some loader valves are that way) - in such a way that you can get an application to work without simultaneously providing for PB. But I think he is just explaining that for the sake of completeness because occassionally you will run across a tractor plumbed that way. That type of non-PB valve is perfectly suitable for one hydraulic application - like a loader. Nobody recommends that you do so by choice, because then you are limited and cannot use a second valve in the fluid line. If you try to put another valve in series in the fluid line you will get back pressure and weird effects. That is what happens sometimes when you hear of someone who has plumbed a tractor in such a way that when they raise the 3pt hitch the loader will move....things like that.

 

[lens12]

An open center & a closed center valve are 2 different valves. An open canter can be installed with PBY(3 hose) or without PBY.(2 hose). The technically correct way is 3 hose. It can be installed as 2 hose, but resistance from down stream valve may cause operating problems.

 

[roger_scotty]

This thread is educational in another way because as near as I can tell, all of us are saying the exact same thing but in different words.
In summary: open and closed center systems have completely different pumps and valves. The parts are not interchangeable. Most compact tractors are open center. Most implements don't care.
Only an open center valve with a Power Beyond port has the 2 vs 3 hose plumbing option. You can plug the PB port with a special plug and use 2 hoses only if nothing else is on the hydraulic circuit. Otherwise use 3 hoses, with the hose from the PB port powering the next valve in the series.