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.