How do you adjust a hydraulic valve?

WhiteRock · Feb 21, 2005

Where is the pressure is coming from? This still hasn't been addressed. The cylinder must have pressure to work. When the closed center valve is closed, all the fluid happily goes to the power beyond. When the closed center valve is open, all the fluid happily goes to the power beyond. With no pressure at the power beyond, the cylinder doesn't work.

Whether or not the closed center valve is connected before the FEL inlet or after the FEL power beyond outlet will make absolutely no difference. 

There is definatly a difference. When the FEL is activated, the pressure on the pump side will rise proportional to the load on the FEL all the way up to the PRV. If there is no power beyond load, then the pressure will be low even with the FEL lifting.

Why is this a difference? I think it is different because; if the closed center valve is on the power beyond side, it still shouldn't work because of low pressure. On the pump side, the FEL activation will raise the pressure during activation to give a working pressure to the closed center circuit.

I think the bulb will go on for me when the definitive pressure on the closed center circuit is defined. So far it has been a speculative pressure, or I have missed it. I don't mean to be a pain, but I am really trying to understand this.

Henro · Feb 21, 2005

The system has to have at least the 1500 PSI all the time or even the 2300 PSI design pressure flowing through it at all times, otherwise the power steering and the hydro wouldn't work. 

Junkman, there is a "Flow priority valve" after the pump and before the loader control valve. It feeds the first 1.8 US GPM to the power steering, and the rest to the 3PH control circuit, according to the BX2200 workshop manual.

Generally fixed displacement pumps output flow, not pressure. Pressure is developed as resistane to flow is encountered. A cylinder that reaches the end of its stroke is an example of where resistance maxes out, the pressuer peaks, and the pressure relief valve trips as the result.

The power steering works because fluid flows into the cylinder, pushing the piston in one direction or another. Pressure will depend on resistance to movement of the cylinder, and would not generally be a fixed amount like 1,500 psi, or something high like that.

We need to keep in mind that flow X pressure = Power, just like Voltage X current = Power in the electrical sense.

(By the way, I did follow your directions and found the layout drawing in the manual at the Prince Hydraulics site...)

 Whether or not the closed center valve is connected before the FEL inlet or after the FEL power beyond outlet will make absolutely no difference. The FEL valve has absolutely and positively nothing to do with the correct operation of Junkman's valve. 

MadRef (or anyone),
<ul type="square">
[*] Where do you see the pressure coming from to operate the cylinder connected to that closed center control valve, if it is connected by tee into the existing open loop circuit? Normally that point should feel relatively low PSI, shouldn't it?

[*] What is your best guess as to what that pressure would be in PSI?

[*] Why do you think a significant amount of PSI would be available to the closed center control valve, if you do think this is the case? What would cause the pressure to be there?[/list]
Could somebody please check out my previous post, tear it apart, seperate the fact from the fiction and list the fiction here so I can see where the logic is flawed? /forums/images/graemlins/confused.gif

I'm the first to admit is it easy sometime to miss the obvious.

Here are two examples:

1) If you hook a hose between the two fittings on a double acting cylinder, it will not "float." The reason is because the volumes are different in each side. It will actually lock up, more or less. /forums/images/graemlins/blush.gif

2) The pressure at the "pump end" of a open-center hydraulic loop will not be zero, but will be some value greater than zero, due to the resistance to flow of the loop. One might at first tend to think that pressure would be next to nothing, when nothing is being operated. /forums/images/graemlins/blush.gif

WhiteRock · Feb 21, 2005

Henro, If you have a workshop manual for a BX2200, can you post the hydraulic schematic? Can we figure it out this way?

We know there is pressure on the closed center valve because it works. I don't believe Junkman is exempted from the laws of physics. /forums/images/graemlins/grin.gif

MadReferee · Feb 21, 2005

( Where do you see the pressure coming from to operate the cylinder connected to that closed center control valve, if it is connected by tee into the existing open loop circuit? )

Henro, using your own words:
 Pressure is developed as resistane to flow is encountered. A cylinder that reaches the end of its stroke is an example of where resistance maxes out, the pressuer peaks, and the pressure relief valve trips as the result.
The power steering works because fluid flows into the cylinder, pushing the piston in one direction or another. Pressure will depend on resistance to movement of the cylinder

Pressure is developed when the spool of the closed center valve is actuated. At this point the CC valve's inlet is opened and fluid flows thru the work ports against the cylinder generating pressure. Exhaust fluid is returned to tank thru the CC valve's outlet.

( What is your best guess as to what that pressure would be in PSI? )
I have no idea and don't really care since it will depend on the cylinder.

( Why do you think a significant amount of PSI would be available to the closed center control valve, if you do think this is the case? What would cause the pressure to be there? )

If the valve is actuated and a cylinder is present that wants to move then there will be pressure. You said so yourself and I am agreeing with you /forums/images/graemlins/ooo.gif

WhiteRock:

( There is definatly a difference. When the FEL is activated, the pressure on the pump side will rise proportional to the load on the FEL all the way up to the PRV. If there is no power beyond load, then the pressure will be low even with the FEL lifting. )

Who cares what the FEL is doing or where the CC valve is connected. So you are telling me that if one of the FEL valve's spools is not being activated then the CC valve will/will not work? Or are your telling me that if a FEL valve's spool is activated then the CC valve will/will not work? I am not sure what you are trying to say.

A power beyond valve passes all fluid straight thru unless a spool is activated. If a spool is activated, unused flow is passed straight thru the valve. That is power beyond.

The FEL spools are essentially in parallel with the flow same as the entire CC valve. When multi spools are activated, even if they are on different valves (this is important), the spool that needs the least pressure for its cylinder will operate first, then the cylinder with the next, and so on. The closed center valve is also in parallel with the flow and acts the same.

A single spool being activated will typically not use the total flow.

Pressure is generated when a spool is activated and a cylinder needs to move.

Junkman · Feb 21, 2005

( I don't believe Junkman is exempted from the laws of physics. /forums/images/graemlins/grin.gif
)

Does this mean that if I violate the laws of physics, that I am going to TBN jail???????? /forums/images/graemlins/grin.gif

The 1500 PSI that I measured was at the end of the hose when the valve was operated. If I had a camera, I would post a picture of this. Hopefully I will have a new one tomorrow and will be able to post more pictures. Junk in jail. /forums/images/graemlins/frown.gif

WhiteRock · Feb 21, 2005

You write as if you think the CC valve is connected to one of the power beyond ports. Is that he case? That is not what Junkman said. He said it was connected in front of the FEL valve on the pump side. I don't believe it will work there.

Can you use this Diagram on page 10 for reference and tell me that you think this should work by plugging the CC valve into the pressure gauge?

That is what I am understanding you to be saying. /forums/images/graemlins/confused.gif

WhiteRock · Feb 21, 2005

Does this mean that if I violate the laws of physics, that I am going to TBN jail???????? 

Nope, These laws were made by an executive branch beyond imagination! They can't be broken. The really cool thing is that we don't need lawyer's to interpret them. /forums/images/graemlins/cool.gif

The 1500 PSI that I measured was at the end of the hose when the valve was operated. 

Is there anyway you could have plugged into one of the optional power beyond ports?

Junkman · Feb 21, 2005

( Is there anyway you could have plugged into one of the optional power beyond ports? )

Not unless someone changed the plumbing while I wasn't looking and then put it back after I took the reading. To add another dimension to this, I took a reading at the end of the hose on the loader valve that goes to the lift cylinder and that reading was 2300 PSI. Please keep in mind that these readings were at the hose end where the disconnects are that normally hook up to the cylinders. I have not taken any readings where the gauge is hooked up in parallel with the cylinders in a working environment. I will do that some time this spring when the loader is reinstalled and the snowblower is removed. Do you think that this thread will continue that far into the future?????? /forums/images/graemlins/grin.gif /forums/images/graemlins/grin.gif /forums/images/graemlins/grin.gif Almost forgot to mention.... I increased the engine RPM and the readings in both instances increased.

MadReferee · Feb 21, 2005

( You write as if you think the CC valve is connected to one of the power beyond ports. Is that he case? That is not what Junkman said. He said it was connected in front of the FEL valve on the pump side. I don't believe it will work there.
)

That's what I think and that is what I said. It will work there or anywhere else in the circuit. There is only one power beyond port on a valve and it is connected to the inlet of the next valve in the circuit. In other words, the PB port of the previous valve is the same as the inlet of the next valve. It's all the same line so to speak.

I assume you mean the diagram on page 18 not page 10. If you remove the pressure guage and connect the CC valve's inlet there and tee the outlet into the return line it will work fine. Same if you tee the CC inlet anywhere in what they call the pressure line between the 2 valves (the line that goes from the bottom PB port to the upper valve's inlet).

BRAVO_WHISKEY · Feb 21, 2005

I've been following this post from infancy. I understand most hydraulic principles, but I too am confused on this one. Junkman's grapple valve is closed circuit teed to the loader supply. When he opens the grapple valve it moves the grapple. This tells me that the open circuit has inherent pressure even when the circuit is simply from pump straight through the FEL valve and back to pump (meaning neither FEL valves are open). If there is no pressure in the open circuit, opening the grapple valve wouldn't do anything since the CC valve is not a diverter but simply a gate. The hydro fluid would want to follow the path of least resistance (which should be the open center valve) and not flow into the grapple valve. Does this make any sense? If there is no inherent pressure in the open center system what makes the hydro fluid flow to the grapple? I know I'm still confused.