Re: Hydraulic basics - I need help

Posted by Bill from up north on November 11, 2001 at 21:39:37 from (205.200.30.213):

In Reply to: Hydraulic basics - I need help posted by Bill Oakes on November 11, 2001 at 19:13:59:

An open center system is one in which the pump is pumping oil continually through the spool and back to resevoir.The pump associated with this style of system is usually a gear or positive displacement piston pump. The oil flows under little to no pressure through the remote spool until you move the lever on the spool to divert oil to a cyl or some other demand. Even then only enough pressure is built up to do the work required unless the amount of work required exceeds the pressure setting on either the release valve for the spool or the one for the pump.
A closed center system is usually associated with a variable displacement piston pump where the pump builds up pressure to a specified pressure setting ,no oil flows through the spool when it is the neutral position and a signal line to the pump(can be internal in the pump) drops the pump displacement to zero. When you move the lever on the spool to do work , the line pressure drops because oil is being allowed to flow so the drop in pressure causes the pump to increase pump displacement and start pumping oil. Pump displacement varies with demand as the pump tries to maintain the preset line pressure of whatever the system is set for eg.2500lbs.
3 way and 4 way valves is simply the no. of different directions oil can be diverted by a particular valve or valves.
Power beyond -- Most cheap spools merely divert all of the oil coming through the inlet side to whatever direction you move the spool . A power beyond valve only diverts a portion of the total flow of oil coming through the inlet side and allows the remainder of the oil flow to travel beyond to the next valve so more than one operation can be accomplished at the same time.As far as I know all hoes are equipped with power beyond so you can actually operate all functions at the same time. Hope this helps some !
A 4000 ford doesn't have enough pump capacity to operate a hoe. You would be better to install a pto mounted pump on it - at least that was my experience with my 4000.

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