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jdemaris
12-05-2003 18:38:15
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Re: Re: Re: Closed center hydrolics in reply to Paul, 12-05-2003 10:00:11
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A lot of John Deere equipment uses closed center. When I worked as a JD mechanic, I
was often taught at Deere school that the closed center system was better than open
because there was always high pressure oil at the control-valve, ready to use, and
therefore response was faster. Sounds good, theoretically, but in my real-life
experiences, I can't feel the difference. As I recall, the term "closed center" refers to the
center of the main control valve being normally closed, whereas, and "open center" has a
control valve that is normally open, so oil flows through it all the time with virtually no
pressure - until a function is used. My own opinion is, the open center systems are simpler and work just as well as closed
center systems. And, open center systems don't cause the engine cranking and starting
problems often associated with closed systems. One other benefit to open-center is that
the components, especially the pumps, are usually generic and easily replaceable. Webster pump craps out, just replace it with a Cesna or Vickers, etc. On the other hand,
closed-center systems often utilize proprietary components. Take a John Deere closed
system, especially an older one, and try to retrofit a pump, steering valve, or selective
control valve with anything but a John Deere component and you'll be out of luck.
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