Hydraulics limitations

[soulasphil]

I have some problems with hydraulically hooking up implements to my JD 3520. Trying to find better solutions led me to realize I didn't understand much of how the hydraulics of my tractor work.
Why is it that I cannot lift and tilt the loader bucket at the same time?
How come using the cylinders to change the height or slope of the hedge trimmer stops the hydraulic motor on the cutter bar?
I would have thought that with 8.6 gpm for implements, the pump delivered enough to do several things at the same time.

 

[AKKAMAAN]

I have some problems with hydraulically hooking up implements to my JD 3520. Trying to find better solutions led me to realize I didn't understand much of how the hydraulics of my tractor work.
Why is it that I cannot lift and tilt the loader bucket at the same time?
How come using the cylinders to change the height or slope of the hedge trimmer stops the hydraulic motor on the cutter bar?
I would have thought that with 8.6 gpm for implements, the pump delivered enough to do several things at the same time.

try to increase engine (pump) rpm's to the max, and see if that makes ANY difference. Also make sure your spool valves make full travel (max diversion of flow to cylinder motor)....

Also, in a constant flow system (open center), flow will prioritize the lowest resistance first....which means that the cylinder with lowest load pressure will move first....unless you with control valve retsrict flow to the light loaded cylinders

 

[J_J]

I believe that the first upstream spool activated will have priority over other spools. If the first spool is not using all the GPM's from the pump, another spool can use what is left over.

If the motor spool is say the third valve in line, then it will use the available flow to operate the cyl, and when released, the motor will get full flow. .

 

[deputy11]

Mine will lift tilt, lower dump at same time. Takes practice to find just that right touch on the joystick.

 

[AKKAMAAN]

I believe ???? that the first upstream spool activated will have priority over other spools.

Most multiple spool valve have a parallel flow supply to the port when center gets restricted.....

If the first spool is not using all the GPM's from the pump, another spool can use what is left over.

there is no such thing as a "first spool"...they are supplied parallel to the work ports....

EDIT: Picture from page 5 in this Prince valve PDF

 

[soulasphil]

In Tips & Troubleshooting, John Deere mentions some form of regulation between the competing demands. The explanation doesn't strike me as very clear, and of course that is in the case you remain within the capabilities of your hydraulic pump :

" One major difference between a Selective Control Valve (SCV) and Power Beyond is an SCV has pressure/flow compensation whereas Power Beyond does not. An SCV section has an internal component referred to as a pressure compensator valve. The pressure compensator valve acts as a pressure regulator in the SCV section to maintain constant flow regardless of any other hydraulic function used.
For example, a hydraulic motor running on SCV #1 may require 10 gallons per minute of hydraulic flow at 1500 psi. If SCV #2 is engaged to run another hydraulic function that requires 6 gallons per minute at 2000 psi, the compensator in SCV #1 will balance this pressure change from hydraulic pump and maintain steady operation of the hydraulic function from SCV #1. "

 

[J_J]

Are all loader valves parallel?

Maybe this is what I was thinking.

• Parallel (V20P): Valve sections see common (parallel) inlet oil. If two spools are actuated simultaneously,
the oil will take the path of least resistance unless the lightest loaded spool is throttled back to
limit flow. A fully shifted spool blocks all oil available
to the power beyond core.

• Tandem(V20T): Sometimes referred to as a priority
section or series/parallel design. Valve sections see
common inlet oil. If two spools are fully actuated
simultaneously, the upstream section will always
have priority for oil over any downstream sections.
A fully shifted spool blocks all oil available to the
power beyond core.

 

[AKKAMAAN]

deputy11 hit the nail on the head..."Takes practice to find just that right touch on the joystick.".....and the "touch" will differ depending on how the actuators are "loaded"

this is how "all" multiple spool valves basically are designed, open center flow is going through the the spool valves in series (blue).....each spool valve can restrict the flow to pressurize the "power core" (red), and then each spool valve can direct oil to each actuator simultaneously....

Note:
(Plumbing a series of individual electric solenoid valves, would not allow this parallel connection, and the valve will not allow INDEPENDENT simultaneous operation. Operating two valves at the same time would connect the actuators into a series. To operate multiple individual solenoid valves independently and simultaneously, require closed center plumbing.)

 

[soulasphil]

In spite of all my efforts, I've never been able to lift and tilt the FEL bucket at the same time on my JD 3520 300CX. I have to stop lifting and change the inclination of the bucket, then resume lifting. Waste of time and efficiency.

Now I have another grudge against my hydraulics. Why is it that when I use the 3rd SCV to operate an implement connected to the rear QCs, I cannot use the 3 point hitch or the FEL at the same time ? This is also very annoying : when I have the hydraulic hedge trimmer at the back of the tractor, it would be very convenient to be able to raise or lower the FEL to avoid obstacles, etc.

 

[J_J]

If the FEL is only using, say half of the available flow, then the 3pt should be able to use the other half. Same with lift and tilt. The hedge trimmer should run at full speed if the FEL is not being used. It will slow down if the FEL is used.

 

[soulasphil]

The problem is as soon as I open the 3rd SCV to activate the hedge trimmer, the log splitter or the dump trailer, all other hydraulic devices like FEL or 3pt are cut off, that is very annoying and I wonder why Deere designed it that way.

 

[J_J]

The routing of the hyd fluid could probably be modified to accomplish what you want to happen. The first valve after the pump should have priority. Valves downstream use what is not used by upstream valves. Steering hyd is a high priority. Do you have a hyd schematic to see the routing of the fluid.

 

[kennyd]

The problem is as soon as I open the 3rd SCV to activate the hedge trimmer, the log splitter or the dump trailer, all other hydraulic devices like FEL or 3pt are cut off, that is very annoying and I wonder why Deere designed it that way.

Deere didn't "design" it that way, it's just the nature of the system for the money you spent. To have a system that would supply all of the different functions at once would cost more money.

 

[soulasphil]

Unfortunately, I only have the owner's manual and no hyd schematic, pity that would certainly help. Besides it is difficult to understand the plumbing from looking at the tractor as many links are internal. Steering and other utilities have their own separate hydraulic pump, so I'm only looking into implement hydraulics.
I don't think it's a question of money. For instance I can use the FEL and 3 pt hitch at the same time, but I cannot use the FEL and 3rd SCV at the same time. There clearly is a difference and I would like to know why.

 

[J_J]

Can you determine where the fluid goes first? Otherwise, does it go to the FEL first, or go to the back first? Is the tractor open center, and can you follow the flow through the system. If in fact it goes to the FEL, and then to the 3rd SCV, and then the 3pt. If the hyd hedge trimmers are running, they would be using all the fluid in the series loop, and the 3pt would not get any. If you ran the hedge trimmers at half speed, then the 3pt should work, although not as fast. Probably as soon as you turn off the hyd hedge trimmers, you should have 3pt. If you are only using some of the flow for one circuit, there should be some flow left for another circuit.

Does your 3rd SCV have PB?

You could put hyd gage in the circuits to test and trouble shoot the system.

JD 3520

Hydraulics
Type Open Center

Pump Rated Output, gpm (L/min.) 13.9 (52.5)

Steering 5.3 (20)

Implement 8.6 (32.5)

Pump Type Dual gear

Maximum Operating Pressure (PSI) 2500

Draft Control Type Position control

Remote Control Valves Available 5

 

[soulasphil]

Thank you very much J J for trying to help me understanding those mysteries. I'll go under the 3520 some more to try and follow the hyd lines. I do not have power beyond but am thinking of having it installed.
From the beginning, you take for granted that the different outlets share the available oil and some of them have to slow down when others are turned on. That is exactly the case with the positioning cylinders of the hedge trimmer and its motor. But it is not the case with the 3rd SCV. As soon as it is in one of the 2 active positions (not the float position far forward) the rest of the tractor's hydraulics is cut off, the controls dead. And this is true even if no oil is used (log splitter stopped for instance). I find it difficult to understand how this can be achieved.

 

[J_J]

soulasphil

I noticed that your avatar is a sailboat, but did you know that a ferro cement sailboat was built, and is operational. Here are some pictures of the hull with a steel grid frame, the finished cement hull, and the fitted out sailboat.

 

[soulasphil]

Yes I know there are concrete hulls for sailboats. I have seen a few and even had drinks aboard one of them. I don't know about America, but in Europe they are no longer in fashion.