How do you adjust a hydraulic valve?

[Henro]

<font color="blue">In the original post Junkman said he was using a closed center valve. Since fluid does not flow thru the valve when the spool is in neutral, a closed center valve will work in this application when teed into the loader lines. </font>

MadRef,

The thing that puzzles me is that since the closed center valve is tied into an open center system, I wonder where the pressure is coming from to activate anything tied to the closed center control valve. Since the open center system develops little or no pressure in the loop until one of the open center control valves is operated. At that point pressure is developed between the pump and the activated control valve as you know.

Junkman, are you able to activate the grapple [I saw the other thread on your grapple (again, forgot about it)after posting to this one today] when your loader control valve is in the neutral position?

It just seems to me that hooking up like this could introduce a lot of variability into the operation of whatever is connected to the closed center control valve. I could be all wet here. I am just asking because I am curious.

What I would expect to see happen, IF the closed center control valve is hooked between the hose on the inlet side of the loader valve and the return to tank hose, is that when the loader valve is centered there would be very little pressure to close or open the grapple (again, I assume it is controlling the grapple). BUT if the loader valve was operated, then the pressure available to the grapple cylinder would increase, relative to the load felt by the loader cylinders being operated. Up to the point where a PRV tripped.

I guess what I am really wondering is if Junkman's original question related to adjusting system pressure might relate to having a closed center valve TEEd into his open center system?

It sure looks to me like with a closed center valve TEEd into the open centered system, the pressure available to Junkmans closed center control valve could vary anywhere between very little and up to maximum system pressure, depending upon what was going on with his loader at the time.

Appreciate your comments on this!

 

[Steve_Miller]

I'm seeing and reading the same thing Henro is here. I'm puzzled as to how it will work too until you use any function on the loader valve? Henro, I think i'm all wet here too?

Steve

 

[MadReferee]

Henro,

You are missing a basic point about open/closed center systems. An open center system has a fixed displacement pump that is always pumping and valves that pass thru fluid when in neutral (because the pump is always pumping). It's a loop system with continuous flowing fluid. A closed center system has a variable displacement pump that typically only pumps when fluid is needed to move something and the valves block fluid from passing thru when in neutral.

In Junkman's application, when the CC valve is in neutral, it's inlet is pressurized, so to speak, because it is teed into the loader pressure line and the fixed displacement pump is constantly pumping fluid thru the OC portion of the system. The CC portion is sort of like a dead end road with a gate on the end. Once the CC spool is activated fluid flows thru the spool to the work ports, to the cylinder and the cylinder returns back to tank.

I hope that explanation is simple enough.

 

[Junkman]

</font><font color="blue" class="small">(
Junkman, are you able to activate the grapple [I saw the other thread on your grapple (again, forgot about it)after posting to this one today] when your loader control valve is in the neutral position? )</font>

The valve works fine operating the grapple in the summer and the snow blower chute in the winter. I purchased a hydraulic gauge when I had other things on order at Surplus Center and just thought that I would give it a try to see what the operating pressure was on my BX. I remembered another BX owner that had a low pressure problem, and that was my reasoning. After checking the loader valve, I checked the grapple valve and found the setting to be lower. I like the lower pressure for operating the snowblower chute motor. In fact, I was wondering about lowering the pressure for the chute motor, if that would make the motor turn slower? I like the present speed, but it has too much torque and when it reaches the end, it can do damage. If the pressure were lowered, then this problem might be eliminated. The valve is a Parker Closed Center Valve.

 

[Henro]

<font color="blue"> You are missing a basic point about open/closed center systems. </font>

MadRef,

I forgot to add to that last post that I join Junkman in saying that when it comes to hydraulic questions, when I read them here the first thing that comes to mind is "MadRef will help this guy out!"

So I don't want to appear like I don't appreciate all the great help you give people here, because I really do.

But I don't think I am missing any points. Here is my reasoning.

If a closed center valve is TEEd into an open center system, and the open center loop is never closed by one of the open center valves in the loop, where does the pressure come from to operate something connected to the closed center control valve?

Granted we don't live in an ideal world and there is some pressure developed in the open center loop due to flow restrictions in the tubing of the loop. What would this amount to? 5 percent of PRV setting?

So please explain where the pressure comes from to operate whatever is connected to the closed center valve in Junkman's system, when the tractor's other control valves are centered and the loop is open between the hydraulic pump and the tank.

<font color="blue"> I hope that explanation is simple enough. </font>

Obviously, it wasn't... /forums/images/graemlins/smile.gif

Once ths question is resolved we can move on to the next one... /forums/images/graemlins/grin.gif

 

[Henro]

Junkman,

Can you tell us how you actually checked the pressure of the "system" vs the "grapple valve?"

The reason I am asking is after posting that last reply to MadRef I am now wondering about my assumption that the pump pressure, when pumping into the open center loop would be maybe 5% of PRV setting.

I wonder if anyone has checked system pressure on the pump side of the loop with all control valves centered? I know I was surprised by the small tubing used in the adapter block I installed on my B2910 when adding T&T. It could be that the flow resistance in the BX is high enough for 1500 psi to be developed at the pump, when the pump is pumping through the normal open circuit loop (all control valve in the center).

Perhaps what you measured when checking the closed center valve for your grapple was the pressure developed by the pump when pushing the fluid through the open loop.

That would make sense and explain why your set up would work in a practical real world situation, when it should not in a theoretical world... /forums/images/graemlins/smile.gif

I would also suggest a possible additional test you might do. You could measure pressure at the grapple valve while operating the loader bucket to the end of its travel, until the system PRV trips, and see what the pressure reads at the grapple valve then.

 

[Steve_Miller]

I'm still with you Henro. Maybe this will help, if not confuse, but from what I'm assuming the Grapple/chute valve is in parallel with the loader valve, correct? If so, with the loader valve being open center there is no pressure across the pressure and return side in the neutral position, correct? So like Henro states, virtually all fluid being pumped into the circuits returns to the tank thru this path, correct? Even if you shifted the grapple valve the path of least resistance is still to the tank because a return line is usually bigger so that there is no restrictions to flow, correct? We need to get me straight on this one before I go to bed or I'll lay there with hydraulic fluid running out my ears.

Steve

 

[MadReferee]

</font><font color="blue" class="small">( If a closed center valve is TEEd into an open center system, and the open center loop is never closed by one of the open center valves in the loop, where does the pressure come from to operate something connected to the closed center control valve?)</font>

Pressure is always there because the pump is always pumping fluid thru the system. Almost, if not all, CUT's have a fixed displacement pump that is constantly pumping fluid. This pumping action generates pressure. Your B2910 is pumping 6.4 gpm at 2600 rpm under no load conditions. Your system relief valve, which restricts the max pressure in the implement circuit, is set to between 1920 amd 1991 psi. Thus, as long as the engine is running you have pressure. See section 8 of your WSM for additional information.

Here is a better example. Connect your green garden hose to the spigot. Connect a tee to the other end and connect 2 hoses, one white and one blue, to the tee. Leave the white hose open. Connect a pistol grip on/off spray nozzle to the blue hose. Turn the spigot on.

What you now have is an open center system (green/white) with a closed center leg (blue) along with a fixed displacement pump (the spigot). Water (fluid) flows thru the green hose and into the blue and white hoses. The white hose is open and continually flows water. This is the open center circuit. The blue hose with the on/off nozzle is the closed center part of the circuit. When you open the nozzle you get water flow. Same as Junkman's configuration only his is hydraulic. Same principle.

 

[Steve_Miller]

<font color="orange"> The blue hose with the on/off nozzle is the closed center part of the circuit. When you open the nozzle you get water flow. </font> I wish I could suck this in, but if you put a pressure gauge at the nozzle, how much pressure would you get? My guess would be only a few psi. which is created by the restriction of the hose diameter, not the pressure that you would see if the white hose was shut off.

/forums/images/graemlins/confused.gif This is me?

Steve

 

[MadReferee]

</font><font color="blue" class="small">( If so, with the loader valve being open center there is no pressure across the pressure and return side in the neutral position, correct? So like Henro states, virtually all fluid being pumped into the circuits returns to the tank thru this path, correct? Even if you shifted the grapple valve the path of least resistance is still to the tank because a return line is usually bigger so that there is no restrictions to flow, correct? )</font>

I assume that by saying "return side" you mean the return to tank outlet? If so then you are correct. If you mean the PB outlet then you are incorrect.

Open center valves pass fluid thru the valve from inlet to power beyond when the valve's spools are in neutral. The return to tank outlet is only used for work port exhaust fluid and depending on valve design, also can be used to return fluid when the relief valve pops.

Remember, if fluid is flowing there is pressure. Fluid flows when the engine is running.

Also, a valve spool that is activated almost never uses all available flow. If it did then the lift/curl dual function of the joystick loader type valve would never work.