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Crawlers, Dozers, Loaders & Backhoes Discussion Forum

Allis Chalmers H4 Crawler/Loader

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Squaaty

08-02-2007 12:19:29




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Does anyone know if the hydraulics is of the Open or closed center type?




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jdemaris

08-02-2007 14:18:53




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 Re: Allis Chalmers H4 Crawler/Loader in reply to Squaaty, 08-02-2007 12:19:29  
Closed center with a gear pump.



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135 Fan

08-03-2007 22:35:11




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 Re: Allis Chalmers H4 Crawler/Loader in reply to jdemaris, 08-02-2007 14:18:53  
Just curious but I thought closed center needs a variable displacement or special pump so it doesn't dead head. Is there such a thing as a closed center Gear pump? Dave



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J Schwiebert

08-04-2007 08:30:56




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 Re: Allis Chalmers H4 Crawler/Loader in reply to 135 Fan, 08-03-2007 22:35:11  
You are not wrong on your thinking, but there are a number of closed center systems out there with gear pumps. They all have some form of an unloader to unload the pump.



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jdemaris

08-04-2007 07:31:19




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 Re: Allis Chalmers H4 Crawler/Loader in reply to 135 Fan, 08-03-2007 22:35:11  
I "mis-spoke", I meant to say "open center." Sorry - maybe I'm getting senile.

By definition - and "open center" system has an open center in the main hydraulic control valve - meaning oil flows through it ALL the time regardless if any functions are being used. A "closed center" has a main hydraulic control valve that is CLOSED in the center - meaning all oil flow is cut off when no functions are being used. So, a closed-center type pump usually needs to be variable capacity and have the ability to pump zero flow.

Obviously, if you stuck an open-center type pump onto a closed center valve - it would probably blow up (I've seen it happen many times).

Sorry for my bad post - I guess I'd better start proof-reading.

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