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Firefighteryoung, here�s a little bit about the H Power Lift system. First, you have bragging rights because the H Power Lift system was the first true live hydraulic power system offered for any Two Cylinder tractor manufactured by John Deere. Others of that era were powered via the power shaft and needed the clutch to be engaged in order to function. Now, on to the operation - - The H Power Lift that you bolted on to the end of your governor housing is comprised of a small gear pump that is rotated by the governor shaft, a reservoir for the hydraulic oil, a simple directional control valve that permits operation of a single-acting cylinder, an integral pressure relief valve, a check valve that prevents the return of oil from the cylinder (until the operating handle is pushed down), a simple, adjustable-orifice flow control valve that controls the return flow rate (controls the implement drop speed), and finally, an interesting little unloading valve (called a by-pass valve by Deere). Here�s how it works: The pump causes oil to flow (internally, anyway) anytime the engine is running. The main thing to keep in mind is that the H Power Lift was designed and intended for uninterrupted lifting. That is, once you start lifting (extending the cylinder), the system lifts until the cylinder is fully extended. It was not intended for a lifting operaton to stop in mid-stroke. First, you push the handle completely down which resets (closes) the by-pass valve. Then, you raise the handle to its full-up position. This directs oil to the cylinder causing it to extend, and thus raises the implement. When the cylinder reaches the end of its stroke, the pump pressure spikes and oil is forced past the relief valve. If enough oil flows past the relief valve, the by-pass valve is tripped open, and oil can then flow unimpeded from the pump, through the by-pass valve, and back to the reservoir. Furthermore, the check valve prevents oil from flowing back from the cylinder, and thus the implement stays locked in the raised position. Basically, the lifting is done automatically. You raise the handle and it stays up while the implement raises until full up, and then the system sort of �shuts off� automatically, even though the handle can remain in the full up position. When you want to lower the system, you simply push the lever completely down, to the point where the little links between the lever and the control valve plunger �overcenter� and lock the control valve plunger in the fully down position. Pushing the lever fully down also forces the spring-loaded check valve open, and that permits oil to flow back from the cylinder to the reservoir, thus lowering the implement. But this action also resets the by-pass valve to the closed position. This means the pump oil, instead of flowing through the by-pass valve, is now required to flow to the directional control valve. When the lever is full down, or nearly full down, oil is permitted to flow through the open directional control valve and is directed back to the reservoir. This is known as the �neutral� stage. You should be able to easily lower an implement in stages (instead of one big drop) by �bumping� the lever downward, but it won�t be as easy to �bump� the implement upward, because, when raising, the lever tends to be forced upward by the same internal hydraulic pressure that is causing the cylinder to extend. Of course, once the cylinder has been completely extended and the by-pass valve pops open, the internal hydraulic pressure drops to zero, and accordingly, there is no more force holding the lever in the full-up position, and you can then move the lever up or down freely. Confused yet? As Mike M. mentioned, there was a unique hydraulic cylinder designed for and used only on the model H. Actually, the basic cylinder is pretty simple in concept. But cylinders, in those days, used leather cups on their pistons, and those things were notoriously leaky, as compared to today�s modern o-rings and v-cup seals that are typically used on pistons in hydraulic cylinders. So, Deere came up with a nifty oil-recovery system that actually pumps leaked oil back into the cylinder. How in the world does that work? Well, first, understand that the cylinder assembly consists of the cylinder and a piston that is attached to a much smaller rod. The H cylinder is NOT a �ram�, (which is a big solid rod in a cylinder, without a separate piston), but is constructed similarly to a two-way cylinder, except it is not designed to retract under pressure from the opposite end of the cylinder. Instead, the cylinder chamber nearest the rod end is simply empty. The next thing to remember is that the cylinder MUST be mounted correctly. There are arrows on the cylinder that indicate the proper orientation of the cylinder. If vertically mounted, the end marked �top� (with the �� diameter clevis pin) must be in the higher position, and if mounted (nearly) horizontally, the arrows must be on the top side. If mounted correctly, leaking oil escapes from the pressure side of the cylinder to the empty chamber side, but puddles inside a collection compartment on the non-pressurized side of the piston. Now comes the neat part. The piston is fitted with a little plunger pump. The head of this plunger is moved (depressed) when it contacts the inside of the rod-end cap of the cylinder, when the cylinder is completely extended. When the plunger is depressed, it pushes the recovered oil back into the pressure side of the cylinder, past a little check valve built into the piston head. Nifty!! A hydraulic cylinder that collects leaked oil and pumps it back into the hydraulic system automatically, simply by its own retracting and extending action! A couple of other notes: Because the pump operates continuously, there must always be oil in the reservoir. Otherwise, you�ll burn up the dry pump. Secondly, there were a number of Field Service Bulletins issued for the H Power Lift that were the response to a number of complaints about the system. Basically, the problem was if the engine (and pump) were running slowly there wouldn�t be enough flow through the relief valve (after the cylinder extended fully), and so the by-pass valve wouldn�t trip open. Accordingly, the system would be �dead-headed� and all the pump oil would be forced past the relief valve continuously, and the system would get really, really hot. So, the answer, according to the Field Service Bulletins, was to keep the engine RPM up there � use �rated RPM�. There were also issues with contamination. One Field Service Bulletin recommended adding a pipe nipple to the reservoir fill port to elevate the fill location well above the top of the reservoir to prevent dirty from entering so easily during fills and oil level checks. Another bulletins advised oil changes every six months in order to avoid the possibility of water infiltration. Water might freeze and really mess up the system. Hope I haven't bored you to tears with all this information, but that little Power Lift for the H is quite a neat mechanism, and I was impressed with its features and concepts.
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