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Circuit idea: two-speed log splitter

Feb. 18, 2014
If you have a wood-burning fireplace or stove, this long, cold winter may have depleted your stockpile of firewood. And if you’re like most fluid-power aficionados, you’ve dreamt of applying your knowledge to build your own hydraulic log splitter.

If you have a wood-burning fireplace or stove, this long, cold winter may have depleted your stockpile of firewood. And if you’re like most fluid-power aficionados, you’ve dreamt of applying your knowledge to build your own hydraulic log splitter.

Most commercially available log splitters use a hi-lo pump, which is essentially two pumps in one — a high-pressure, low-flow pump and a low-pressure, high-flow pump operating in tandem. In normal operation, both pumps route fluid to the cap end of a cylinder. When a wedge mounted to the cylinder’s rod end engages the log, system pressure increases, which shifts the pump into high-pressure mode. In this mode, the high-flow pump is removed from the circuit, so only fluid from the high-pressure pump flows to the cylinder.
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Reader Jean-Louis Bournival, of Vaudreuil, Quebec, proposed the regenerative circuit shown here. It uses unloading valve A set about 120 to 150 psi lower than relief valve B. The circuit provides high extension speed until the cylinder meets resistance and then automatically produces higher force at lower speed until the log splits.

Referring to the schematic, with the directional valve shifted for cylinder extension, pressurized fluid flows into the cap end of the cylinder. Fluid flowing from the rod end is blocked from returning to tank by check valve C. Instead, fluid flows through check valve D and combines with pump flow to extend the piston at high speed. When pressure in the cylinder's cap end reaches the pressure setting of valve A, pump pressure opens it, allowing fluid from the cylinder’s rod end to flow to tank. Check valve D prevents pump pressure from acting on the rod end of the cylinder, so full pressure is applied to the piston from the cap end. Of course, this circuit will perform in other high/low applications.

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