Hydraulic questions

[Momboy007]

Hello All,
I do not completely understand the hydraulics on a tractor, can you help with some questions. I do understand pnuematics fairly well, so I try to compare the 2.
Anyhow, the first question is:
1. What is meant by "power Beyond"?
2. Does the hydralic pump have a high pressure line and a return (low Pressure line) is that how a cylinder work???
3. What is the suction line? is this like a return hydraulic line?
I am trying to better understand the system in order to be able to troubleshoot

Thanks in advance,
Rick

 

[Bird]

Rick, we've got a bunch of members who know more about hydraulics than I do, but I'll try to give you the basics:

1. An open center hydraulic valve means that the hydraulic fluid is flowing through it all the time. When you use the valve, as in moving the joystick for the front end loader, you divert that flow to a hydraulic cylinder. Power beyond means you have a port on the valve to which you can plumb a line to another valve. In other words, the fluid that's always flowing through the first valve then goes to the other valve before returning to the sump.
2. I think of it more as high pressure going to hydraulic valves or implements, then returning to the sump, but I guess your statement is true. There are both single acting and double acting cylinders. A single acting only has the one line to it; pressure pushed the rod out when the valve is opened and when the valve is opened the other way, it simply allows gravity; i.e., weight of an implement to push the hydraulic fluid back to the sump. A double acting cylinder has two lines to it. When a valve is opened one way, pressure goes to one line and the fluid in the other end of the cylinder is allowed to flow back to the sump. Open the valve the other direction and the reverse is true.
3. I think the suction line is the line pulling hydraulic fluid from the sump to the hydraulic pump.

Everyone feel free to add to or correct the above. /forums/images/graemlins/tongue.gif

 

[Momboy007]

Bird,
That actually helps alot.
Thanks,
Rick

 

[bluechip]

I'll just add that in a normal open center hyd system, when a valve is actuated ALL the flow is diverted to that cylinder. In fact there is no real pressure untill the flow is directed against some resistance, like a cylinder with a load on it, then the pressure builds to the point that the cylinder can move (or the pressure relief valve opens). Power beyond allows some pressure to be diverted to another cylinder, even if one is in action, for example on most Jinmas, all the flow from the pump goes to the loader valve, when you are moving the loader, (without power beyond) the only pressure left for the next thing on the line (steering on 200 series, and usually the lift box on 300 series) is the return oil from the back side of the cylinder(s) being moved. If power beyond is used, some pressure would still be availalbe for the steering or lift.

I better quit before I confuse myself....

 

[k8ny]

Actually bluechip, that was an excellent explanation, you taught me something and it sure is hard to teach this dog new tricks.
Very well put and succinct explanation

Bob