Leave the - and W4 out of it.
JohnDB,
I have never seen a tandem pump used for just a loader.
Your description is for a 2 stage pump, and again I've never seen one of them used on a tractor for any use.
Tandem pumps are used when higher flow is desired like to run a hydraulic motor driven device, not higher pressures.
Tractors use tandem pumps to use one pump section to run the loader and a second pump section to run PS and other hydraulic operations.
Newer joystick loader valves typically have anti reverse feedback valves built right into there designs so that dual operations are fine.
You would have to have a really weak / defective pump to have the loader do what you describe, one operation negatively affecting another operation.
I have a B7100 with a loader running off the stock pump, little on the slower side, one because I used 2 1/2" cylinders and 2 its a small pump, but it has no negative operations and the loader is strong enough that it will pick up the entire tractor.
Ah well I guess that's why I'm still an apprentice...
Yes flow is at rated speed.
Thanks for stepping in. I wasn't trying to describe a two stage pump so I'm glad you've clarified it for any readers. I didn't know about the joystick valve having anti-reverse feedback so that's very useful to know thanks! I'm interested because I'm still thinking about a front PTO for my tractor.
But about one operation negatively affecting another ... absolutely it can happen at least on older tractors I am familiar with, Kubota and others. I didn't think their pumps were defective, but maybe undersized for the additional attachment (loader). So you've got me wondering about checking the flow rate. If a pump is rated like my M4500 at 27.5 l/min, is that at rated engine rpm (2600) or some other speed?
I was going to work out the difference in effective volume when closed and when extended of one of the lift cylinders then time how long it would take to stroke it at rated speed. Double the volume because there's 2 cylinders. Do it under load, I was thinking it would give at least an idea if the pump really was stuffed. I'm not so concerned about it that I'd get someone to bring their flow measurement gear here or ship the tractor to a shop. I've also heard of people breaking a cylinder return line and timing and measuring the fluid that emerged when the cylinder was stroked too, but I'm not keen on that approach - fluid waste or contamination risk if reused. The lift rams are single acting. What are your thoughts on either of those scenarios?
I guess that would give you a good base line to work with.
Hi Tim -
) had a relief valve set at about 900 psi; the engine will pop the relief idling. Note that it's easy to overload the front axle; building a loader that will lift 1000 lbs isn't hard, but the front axle of our small tractors won't like that.
Hello Bart (I passed a comment on one of your Youtube videos about your loader.)
I will check but i think it is a D750 engine 18 mm with 22 splines.. or 22mm with 18 splines not sure now. I am in Malta (Europe) shipping cost might not be very helpful...
but it was done in 5 or 6 hours and it is a tight fit - needs a light tapping to go in. I would have loved the idea to have it tall enough to take the sprocket directly! but bad luck. 
