350c hydraulic question

[Bilgerat96]

Hello was just wondering if the blade control valves are a open or closed center valve? Trying to add rear hydraulics to a 350c, believe I have identified the power beyond port. So as long as they are a open center system i should be able to add a open center valve to the power beyond port and plumb in a return line from rear of machine I believe? Thanks for any and all advice.

[Jim B]

Your 350C has an open center system.

A hydraulic system is open or closed. The pumps are different, not just the valves.

[Bilgerat96]

Thank you for the response and it was the answer I was wanting to hear. Never seems to work that way.

[Jim B]

A closed center system has stand-by pressure on it all the time, there is no return flow to the tank when functions are not in use, and the pumps de-stroke when up to pressure. The valves do not use power beyond. Additions can be teed in as the system is always under pressure.

Open center means the pump is pumping oil through the valves and back to the tank all the time. That is why a power beyond port, not just a tee, is needed to route flow to another valve otherwise the flow would go the path of least resistance -- back to the tank, not to power the added function.

Your valve may have a power beyond port, but it may need a sleeve inserted for the power beyond function to work.

[Stan Disbrow]

Hi,

When the JD350 first came out, it was common for Deere to use closed center on the Ag tractors. The idea is that the de-stroking pump doesn't rob power from the PTO shaft. Much of that equipment is quite power hungry and does not need much use of the hydraulics. So, essentially automatically shut down the hydraulic pump when it isn't being used.

This was something not needed over on the Yellow side. So, they used the more common open center system.

I had contemporary JD350 (straight) crawler and 1520 tractor at the same time at one point. Same 3-cylinder engine, but different hydraulic systems. That was rather a PIA if I wanted to hook something up off the back of either machine. Different control valves. So, what I used off the tractor I couldn't use off the crawler and vice versa. Sigh.

I still have a couple closed center control valves hanging about. Left over from converting those closed center things to open center once I had replaced that 1520.

By the mid 70s at the latest, everything went to open center systems regardless of paint color.

Stan

[Jim B]

Hi Stan,

Actually, some of the green ones (and some yellow ones) have continued to use closed center hydraulics for years beyond the 70s, some even up to date. I don't know that the older crawlers ever used closed center systems.

Best regards, hope all is well with you,
Jim

[Stan Disbrow]

Hi,

I have not seen a crawler with closed center, only open.

I haven't needed a ag tractor any larger than that 1520, which was closed center. The replacement 2040 was open center as is it's replacement 5103 I bought in 2008 (which got changed to the current 5045D when Deere completely redid their model numbers).

I can see where the larger machines would benefit from closed center for the same reason it was used in the first place: No power robbing pumping when you don't need to use it. Yet, it is available when you do need it.

There is just too many things in the Deere catalog for me to keep up with, much less buy one of!

Stan

[Lavoy]

The small utility tractors are still open center, but once Deere went to closed center on the ag tractors, they never used open center again. With the strain of all the hyd driven systems on planters and air drills, open center would not do the job, at least not without a ton of heat.
Lavoy

[Stan Disbrow]

Hi,

Well, I was referring to the 3-cyl ag tractors and not the larger field tractors. The ones that more closely fit alongside the JD350 series. These days, they fit into the middle of the lineup between Utility and Field with the 5000 model numbers (they go from the 1000 to the 9000 series these days).

Stan