Quick hydraulic lesson

[VashonFarmer]

I'm a newbie to hydraulics and I've been finding a lot of good info here, but I need a basic question answered.

What is the difference/meaning of "Open Center" and "Closed Center" in reference to hydraulic systems on tractors.

I have a Kubota B8200. Which one do I have?

Thanks

 

[Chilly807]

An open center valve allows free movement of the fluid to and from the cylinder when the valve is centered, essentially a "float" position. The closed center valve "locks" the cylinder in position until the valve is actuated.

Chilly

 

[Just Bill]

This is probably the best explaination available.
http://www.tractorbynet.com/forums/hydraulics/157901-general-hydraulics-question.html[/url][/URL]

 

[VashonFarmer]

Thanks Chilly. I think I'm starting to understand this stuff.

 

[AKKAMAAN]

I'm a newbie to hydraulics and I've been finding a lot of good info here, but I need a basic question answered.

What is the difference/meaning of "Open Center" and "Closed Center" in reference to hydraulic systems on tractors.

Open center system, means that a fixed displacement pump, pumps a constant flow thru the, in neutral, control valve (CV), back to tank. That happens under a relatively low pressure (roughly 100- 400psi), depending on pump rpm's, viscosity and what ever creates back pressure, like return filter, undersized valves, fittings and hoses etc. The flow will be directed to the actuator when the CV is operated, and necessary pressure will build up while the Open center strats to restrict. In neutral CV, the higher "back pressure", the more power losses into heat.

Closed center system, means, usually (not always) that a variable displacement pump, tries to pump a flow, but discharges (displacement goes close to zero). Pump keep a constant pressure to the closed center CV.
The pressure (and flow) will be directed to the actuator when the CV is operated. In neutral CV, the higher "internal leak" in pump and CV, the more power losses into heat.

Usually the Closed center system comes with a lowered stand by pressure when CV isin neutral. Power losses when CV is in neutral, are then minmal compared to an Open center system.

Closed center system, with a fixed displacement pump and a "dump valve", just after the pump, seems to be more common on tractors, that saves a lot of back pressure losses, but require a special control system from the CV.

Hope this explains it for ya!!
Please ask more if needed!!
I am sure others will fill in on this!!

 

[dex3361]

First of all Welcome to TBN. I am not the expert here but I dont think this is the meaning of the terms but here is what my data says: From Baum Hydraulics Corporation
"CLOSED CENTER VALVE- has a blocked “open-center” flow passage thus stopping the pump flow from going to the tank when
the control valve is in neutral position. This can be accomplished by either of two methods. One by the design of the spool lands to
block the flow or use standard open-center spools and block a power beyond sleeve or provide a closed center plug which serves the
same purpose as a plugged power beyond sleeve."

"OPEN CENTER VALVE (Also referred to as tandem-center), has an open center flow passage provided by the spool land
openings that connect the pump flow to the tank when the control valve spool is in its neutral position."

 

[VashonFarmer]

Wow. Thanks guys. This is a truely great place to learn.

AKKAMAAN, I saw your note that JustBill mentioned shortly after I posted the question. Thanks for your willingness to repeat yourself. If y'all keep it up, I might just get it!

I hope to be adding some more implements eventually but don't have any controls other than the FEL. Does this stuff lend itself to the Do It Yourselfer, assuming I get it figured well? I really hate paying people for stuff that I ought to be able to do myself. Even if that means that it will take twice as long and look half as good. Just the way I'm built.

 

[AKKAMAAN]

Wow. Thanks guys. This is a truely great place to learn.

AKKAMAAN, I saw your note that JustBill mentioned shortly after I posted the question. Thanks for your willingness to repeat yourself. If y'all keep it up, I might just get it!

I hope to be adding some more implements eventually but don't have any controls other than the FEL. Does this stuff lend itself to the Do It Yourselfer, assuming I get it figured well? I really hate paying people for stuff that I ought to be able to do myself. Even if that means that it will take twice as long and look half as good. Just the way I'm built.

You will make it, keep a camera handy, post your problems with pictures and drawings...and I am sure the retrofit guys here will guide you thru the process....Good luck!!

 

[cycle_gator]

Vashon Farmer:

Howdy neighbor! I live just accross Colvos Pass from you in South Kitsap, about two miles south of Point Southworth. No luck though, I understand about as much about hydraulics as you do but I am also trying to learn so that I can do some retrofit work on my Kubota L4310.

One way or another, I am willing to bet we can help each other out. I was doing really well until Akkaman (sp?sorry) started talking about a closed center system utilizing a fixed displacement pump with a dump valve after the pump. That just about put me into orbit. I thought I had an open center system, as earlier this year I lost a couple hoses on my backhoe unit, but very little hydraulic fluid as the flow went to zero with the valve in neutral. I just figured the fluid was using the return port to go back to the pump/tank. I have an FEL on the tractor and the backhoe runs off a Power Beyond port on the FEL valve. With the FEL valve in neutral there is plenty of flow into the backhoe, so again I figured open center, but maybe the PB is a special bypass for the closed center?

See what I mean? I am also just completely lost on this stuff. I want to install a set (3) of rear remotes, but I will not do so until late spring 2010. I hope to figure all this out before then so I know what type of valves to buy. But then there are the fittings. Lord have mercy, I have never seen such combinations of swivel and fixed fittings in my life. I will have to plan all this out very carefully to be sure I end up with the correct fittings in the correct places. Nothing worse than trying to screw together two fixed end fittings where one is mounted to a valve or cylinder and the other to a long hose. Most, but not all, my fitiings seem to put the swivel fitting on the part that is most difficult to turn.

Then there is the backhoe with hoses that seem to be designed for failure due to chaffing on the boom/dipper unit. There has got to be a better design to allow these parts to move independently, but have less flex hose and fewer friction points with the hoses. The valve body is very particular about the length of the swages used on the hose ends, so I want to fabricate some steel lines to extend some of those fittings enough to improve that situation, as well.

Just a whole bunch of stuff. Nothing horribly urgent, but definitely in the job jar.

Hope to meet you in person one of these days.

Like I said, nice to meet you. Where on the island are you located?

 

[VashonFarmer]

Cycle Gator

Thanks for writing!

I live out on Maury (the Other Island), but get out your way to see my sister now and then in Olalla.

The 4310 looks like a nice machine. I'm jealous of the BH. What a great tool. I just picked up my B8200 a few weeks ago here on the Island. I don't have the implements that need any additional hydraulics yet, so this is all just speculation on my part. But I am thinking that I would like to add a bucket grapple and will need a new valve. And adding Top and Tilt to the rear is on the radar as well for when I get that box blade.

I looked up your machine on tractordata.com and it states the hydraulic system is "open". That's all it says, but I take that to mean Open Center. What that means for buying a valve is still beyond me. I never realized how complex these systems are.

Keep me in the loop as you get deeper into the project. Would love to see it some time.