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Tractor Talk Discussion Forum

Open or Closed hydraulic?

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Todd (MI)

02-23-2006 15:54:54




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My Allis D17 IV has a "OPEN" center hydraulic system max remote pressure of 2000 and max remote flow of 10 GPM. What is the difference between OPEN and CLOSED center system?




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barnrat

02-23-2006 19:38:05




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 Re: Open or Closed hydraulic? in reply to Todd (MI), 02-23-2006 15:54:54  
One thing that wasn't mentioned was that up until recently you could get greater capacity out of a closed center system. I know Masseys and Deere's closed center systems could get over 20gpm when most other tractors with open center systems at the time were getting 10-12gpm. Open center systems are easier to repair and are lower cost to maintain and repair.



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paul

02-23-2006 18:02:53




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 Re: Open or Closed hydraulic? in reply to Todd (MI), 02-23-2006 15:54:54  
Other ways to say it:

Open center everything is in series through 'power beyond' ports. Closed things are in parrallel.


Open center the pump is always flowing oil, but pressure is variable.

Closed center the pump is always up to full pressure, but flow is variable.

Closed is a little bit better, but either works fine.

--->Paul



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Heat Houser

02-23-2006 16:21:19




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 Re: Open or Closed hydraulic? in reply to Todd (MI), 02-23-2006 15:54:54  
In most valves, the pump output is connected the center passage way. From this passage way the oil will go out first the one work port and then the other depending upon if the spool is pushed or pulled. What happens in the center passage way (also called neutral passage way)when the spool is in neutral is what determines if it is closed center or open.
If the pump output can flow thru the center passage way and directly back to tank with the spool in neutral.....open center.
If the end of the neutral passage way is plugged and the oil cannot flow directly back to tank with the spools in neutral...closed center.
With a closed center system, the pump must be capable of shutting it's self off since the flow cannot get back to tank.
If one looks at a typical cross section of a control valve the arraignment is, neutral passage way, LH work port, LH tank passage way. For the RH side, starting again with the neutral passage way, RH work port, RH tank passage way. The tank passage ways are at the outside ends of the valve castings. (In otherwords, the outside ends of the spools)

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Formerly PaMike

02-23-2006 16:12:16




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 Re: Open or Closed hydraulic? in reply to Todd (MI), 02-23-2006 15:54:54  
On an open center system the hydraulic oil flows from the pump to the valve. When the valve is in neutral(not in use) the oil flows through the valve and back to the tank. On a closed center system the oil flows from the pump to the valve and stops. The only time oil flows back to the tank is when the valve is in use. The hydraulic pumps on closed center systems are setup in such a way that once the hydraulic pressure is reached at the valve the pump "unloads" and doesnt continue to build pressure.

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