|
|
| Am I mistaken in thinking that the return line for a power beyond circuit is returning directly to tank? A power beyond is effectively a connection directly to the pump for the purpose of putting another directional control valve down stream of it, right? And there is no flow control on the power beyond. Is there anything that keeps the power beyond from starving the rest of the valve stack if you were in a condition where cylinder or motor attached to the PB was using all available flow? |
|
| |
|
Mount Vernon, WA | There are actually two return lines on a power beyond valve. One is designed to go straight to sump, and the other is to carry high pressure oil on over to the next valve in series with the first.
The power beyond circuit is not taken directly off the pump necessarily, but rather it is used to power another high pressure function downstream of the first valve. Using a non-power beyond valve upstream of another will subject the exhaust core of the first valve to pressures it is not designed to see, and could crack it. |
|
| |
|
| Depends on the circuit (open or closed center) and the first valve. Usually the first valve takes priority over the flow to power beyond and the load on the first valve gets all the flow it needs, but if it doesn't take all the oil there's some left to go to the power beyond. Return oil from the cylinder or motor doesn't go to power beyond, it goes to the return hose. The first valve usually will starve the cylinder or motor attached to PB no matter how much flow that hydraulic load would take. That first valve priority is what makes power beyond different than hooking valve supply lines in parallel (on closed center, that won't work on open center at all).
Gerald J. |
|
| |
|
| On a Deere tractor there are 4 ports for the power beyond. Do you know the layout off hand of which is which? Also, do you think on modern tractors the valve stack is relieved at 3000 psi with the pump pressure being higher and/or is the power beyond going to be relieved at the same system pressure as the rest of the valve stack? Thanks |
|
| |
|
Mount Vernon, WA | When we talk about power beyond, you're right, it is a night and day difference between open and closed center systems. I don't even think of a closed center, or for that matter, a PFC system, as even needing a power beyond circuit, since you can tee off as many valves in parallel as you want off of the main pump.
My comments in my last post pertained only to open center systems. I wasn't even thinking of closed center. |
|
| |
|
| Those PB on the modern Deere are probably lower priority than the valve the are on. But on the older closed center Deere systems what they call power beyond is just a tap of the parallel pressure supply line with pressure set by the pump control.
Adding a power beyond valve to a closed center system the pressure is set by the pump, there's no pressure relief valve in any of the control valves. Open center the pressure relief in on the supply port, so it limits PB pressure too as does the valve on the PB circuit. PB has to use a valve to control its load or it will accept all the oil flow available, and some loads don't need that.
Gerald J. |
|
| |
|
Mount Vernon, WA | It would be nice to know what model tractor you have. Having said that, most later Deere operator's manuals have pretty thorough instructions for plumbing in hydraulic needs through anything other than the SCVs. |
|
| |
|
| I am actually figuring out what I am going to do for a client to allow him to use the power beyond for a series of Dawn remote control planter attachments. I am going to suggest to him that he run a needle flow control valve limiting the flow from the PB circuit to 0-10 GPM going into the Dawn pressure control stack. I would assume that it is an 8000 series Deere but am not completely sure. He only has 4 remotes. |
|
| |
|
NE SD | Joe, our tractor has high flow hydraulics so it has two scvs on top of a cast piece where there is two power beyond ports, then three more outlets on top of another cast piece with two more power beyond ports. The left,ports are pressure, right ports return to tank. We are using the upper ports to power the VR motors on our planter because we couldn't get the correct fitting to get the seep line out of the way of the lower ports on this tractor. Past tractors have had the lower ports only.
Pressure has never been a problem. These motors do have their own flow control valves though. I think your idea of using a valve to limit flow to the max you will need is probably a good idea. |
|
| |
|
| Could you define for me the difference between a closed and open center system. I hear the terms used a lot but don't know what they are refering to in terms of a hydraulic schematic |
|
| |
|
Nevada, Iowa | Joe, I am pretty clumsy at this stuff but I am in the process of installing PB on an older 8100. In my case, I want to run the blower motor from PB and needed to install a signal line to the top of the valve stack . This signal line is connected via quick couple to a port on an external motor speed control (needle valve). The signal line is to set the pump pressure 290 psi above the motor demand. I am assuming this is to protect the system as well as the motor. JD's PB couple kit literature covers some of this. The kit number is RE217697. My planters tech manual filled in the rest of the pieces. Certain PB applications do not need the load sensing line and I cannot recall which but a JD tech should be able to provide that. I hope this helps. |
|
| |
|
| When I moved a loader to my 4020, I tapped the full pressure (closed center system, not load sensing like more recent tractors) and did put in the needle valve on the supply line to the loader (and a second one for a backhoe) because the tractor pump allows 18 or 20 GPM for the auxiliaries (reserves some for steering and brakes) and I know the loader worked fine with 5 gpm without a need for sandpapered finger tips on the valve handles. With 20 GPM smooth control required more sensitive finger tips than I have. 
Gerald J. |
|
| |
|
| Open center systems, the pump moves oil all the time. The valves pass all the oil they don't need for a cylinder or motor load and the system pressure at idle is only the pressure drop from that flow in the plumbing. Usually very low, probably 30 or 40 psi or less. A restrictive load like a loaded cylinder raises the pressure which is limited by pressure relief valves, usually in the control valves.
Closed center the valve passes oil only to a load, and returns oil to the pump coming from the load, typically the oil from the low pressure side of the cylinder or return oil from the motor. The pump and its controls hold pressure at the system rating, like 2250 psi all the time, destroking the pump when there is no flow.
Each has its advantages and disadvantages. One can argue all day about the pump efficiency in each situation and probably two different pumps for the same scheme from different makers or different conditions will have more difference in efficiency than the other scheme. For sure open center has less complexity at the pump controls. There are none, just the pressure relief valve. But for things like steering and brakes the closed center system probably gets pressure to the critical loads faster than open center that require the pump to build up pressure to force the load.
More modern tractors use a "smarter" system that acts like closed center for the flows but doesn't hold pressure high to cut down on energy lost due to leaks (one of the disadvantages of the closed center system is that with everything at high pressure, leaks get to be expensive energy losses) but has extra controls that sense a load and ramp up the pressure. But shuts down the pump when there's no need for oil so there's less energy used to move oil around the plumbing at low pressure like an open center system does. All at considerable expense and complication in pump control. I've only used open and closed center systems, your customer's tractor is probably one of the newer load sensing systems.
Baum Hydraulics used to have a pretty good section in their catalog on these hydraulic fundamentals. Probably still there if you download the chapters on hydraulic pumps, motors, fittings, and cylinders.
Gerald J. |
|
| |
|
| Thanks Gerald, very helpful |
|
| |
|
Southeast Florida | If its a 60 series or older this is all wrong! This is for a 8X00 and newer setup.
You should have 4 ports on the back if it's factory or dealer kit. If you look on the casting one will have "P" for pressure, "R” for return (which is a pressurized return ahead of the charge pump), "S" for signal (to send pressure to the pump on requirements) and "T" for tank which is use for a non pressurized return usually case drain. If you dump straight into the T port you'll starve the system because the charge /lube pump only makes about 5 GPM. If you need to put a variable flow control on the power beyond it needs to be a special valve for a PFC system. There are other requirements also to deal with the “S” port. You need a shuttle valve plumbed in for pump signal pressure. It’s real easy to do but not every hydraulic shop has knowledge of how to do this and will give a funny look.
Edited by Fla Veggie Farmer 3/15/2011 16:47
|
|
| |
|
| This is very helpful information. Do you think the Deere Tractor manual will have documentation covering this issue? Or is there maybe a whitepaper that the dealer could supply to the customer? |
|
| |
|
NE SD | Never starved our tractor yet returning to "t" with the VR motors. The case drain goes to the trans. |
|
| |
|
Southeast Florida | Does your tractor's power beyond have 3 or 4 ports? |
|
| |
|
| http://en.wikipedia.org/wiki/Hydraulic_machinery
this is a basic explainer. I am going to have to research load sensing systems in greater detail. For instance do load sensing systems acte like a constant pressure system if the load sensing portion is not used. |
|
| |
|
NE SD | 4 that I'm aware of. It's a 9230 JD with 5 scvs.
The PB ports we use are between the SCV outlets. Left marked P and right marked T.
 (PB.JPG)
Attachments
----------------
 PB.JPG (79KB - 615 downloads)
|
|
| |
|
| > For instance do load sensing systems act like a constant pressure system if the load sensing portion is not
> used?
I don't know. My tractors are both 1968 models, one with token closed center hydraulics but came with an open center loader initially with a PTO pump which I changed to a crankshaft driven pump, and the other with a real closed center system with 5 times the flow available.
Gerald J. |
|
| |
|
NE SD | Joe, on the Deere tractors we've had, the PB worked as long as another hyd. was being used. A vacuum fan for example. Deere put a load sense line on our 8220 when we got it and a 1790 CCS back in 2003. In 2004 after they took the planter and tractor back to look it all over, it came back with the load sense line unhooked and we were told to run without it. |
|
| |
|
| interesting point. Because implement design is all I have ever done I have always thought of the tractor as a black box of sorts. Just a power supply. There's a lot going on there.
Are you aware you can do multiple sections with the GFX this year? I also have a different spring rate you may want to evaluate. Jim is going to be in Roscoe for a planter clinic this week. |
|
| |
|
Southeast Florida | That is the reason for the shuttle valve in the signal line I spoke about lower. We still use external control valves on scrappers here from a PB and you need the shuttle valve to power th PB or pull another lever for pressure to build from the pump |
|
| |
|
Far North central Iowa, Northwood | Chad, I'm using PB for the VR motors on my planter. what I don't like is there is a drag from the pump when starting the tractor with the load sense hooked up. so your saying I can leave the load sense unhooked as long as something else is running? In other words the load sense line only function is to provide on/off control to the pump? I was thinking of adding a valve to the load sense line, but unhooking is starting to make sense.
Edited by ddahlby 3/16/2011 08:53
|
|
| |
|
NE SD | We've ran a few different tractors without the load sense line without any problems so far. What I remember being told was that we didn't need the load sense line unless we had problems with the VR motors wanting to surge. |
|
| |
Can we talk power beyond circuits
