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John Deere Skidsteer Forum
1992 JOHN DEERE SKID STEER 675B
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<blockquote data-quote="skidsteer.ca" data-source="post: 26737" data-attributes="member: 307"><p>This is a very basic system (if its related to the NH skidsteer from the 90s) Open center system. Oil from from the reservoir is sucked throught the pump and pressured to the valve (s) that run the boom, bucket and aux hydraulics (3rd valve) Usually a 3 spool valve (sometime a 2 spool with a power beyound and a 2nd single spool valve down stream.</p><p>The return flow is routed through a restrictor valve. It won't let the oil return to the tank until the return flow is raised to the charge pressure used to run the hydros (wheels/ drives)</p><p>What my best guess is that someone has put a "power beyond" valve in the system. This type of valve (or the addition of a insert to convert your valve to power beyond) splits the return flow from the valve into two circuits. One circuit is the flow from when your valves spools are centered (not using the foot pedals) it appears this flow is routed through the restrictor as it should be and you have charge presure under this cituation.</p><p>However if the valve is power beyound when you move a spool (to lift your boom, or tilt the bucket) this oil comes out a separate port on the valve. it would seem the charge pressure from this port is not being restricted, but just returns to the reservoir, and this cause your charge pressure to colapse, turning on the warning and messing up the drive.</p><p>Could you take some pictures of the valve showing the hoses coming and going from it and email it to me?</p><p>If it is a two spool valve it should have 6 hoses if it is not power beyoung. Or if it has 3 spools, then there should be 8 hoses. If yours has 9 hoses (on a 3 spool or 7 on a 2 pools, then it is PB.</p><p>This is my guess with out seeing it, but it seems to fit your senario.</p><p><a href="http://www.mediafire.com/?ov9zqt7xwtl" target="_blank">http://www.mediafire.com/?ov9zqt7xwtl</a> here is a link to more info on the charge pressure circuit.Download the file and see page 264 and 265 in the hydrostatic section for info on how the circuit works.</p><p>Ken</p></blockquote><p></p>
[QUOTE="skidsteer.ca, post: 26737, member: 307"] This is a very basic system (if its related to the NH skidsteer from the 90s) Open center system. Oil from from the reservoir is sucked throught the pump and pressured to the valve (s) that run the boom, bucket and aux hydraulics (3rd valve) Usually a 3 spool valve (sometime a 2 spool with a power beyound and a 2nd single spool valve down stream. The return flow is routed through a restrictor valve. It won't let the oil return to the tank until the return flow is raised to the charge pressure used to run the hydros (wheels/ drives) What my best guess is that someone has put a “power beyond” valve in the system. This type of valve (or the addition of a insert to convert your valve to power beyond) splits the return flow from the valve into two circuits. One circuit is the flow from when your valves spools are centered (not using the foot pedals) it appears this flow is routed through the restrictor as it should be and you have charge presure under this cituation. However if the valve is power beyound when you move a spool (to lift your boom, or tilt the bucket) this oil comes out a separate port on the valve. it would seem the charge pressure from this port is not being restricted, but just returns to the reservoir, and this cause your charge pressure to colapse, turning on the warning and messing up the drive. Could you take some pictures of the valve showing the hoses coming and going from it and email it to me? If it is a two spool valve it should have 6 hoses if it is not power beyoung. Or if it has 3 spools, then there should be 8 hoses. If yours has 9 hoses (on a 3 spool or 7 on a 2 pools, then it is PB. This is my guess with out seeing it, but it seems to fit your senario. [URL]http://www.mediafire.com/?ov9zqt7xwtl[/URL] here is a link to more info on the charge pressure circuit.Download the file and see page 264 and 265 in the hydrostatic section for info on how the circuit works. Ken [/QUOTE]
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1992 JOHN DEERE SKID STEER 675B
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