I pushed through and got the bike hydraulic power system working this evening – it’s pretty sweet. Here’s the overview:
I borrowed a bike exercise stand from my friend Emily and mounted a Haldex-Barnes 11gpm two stage hydraulic pump to it using T-slot extrusion. My friend Keith got a wheel on Ebay and machined a BMX chainring to mate to the left side of it, and I put it on the rear end of my old Bontrager. A short loop of bike chain connects the wheel to a 12T 45 pitch sprocket. The pump draws from a reservoir consisting of a 2 gallon plastic bucket; there’s a plastic mesh strainer clamped over the inlet tube. The pump feeds oil to a 2-position motoring valve. The valve operates a 4″ bore, 20″ stroke hydraulic cylinder. Here’s a detail of the pump and drive:
Here’s the valve and cylinder. The system works as slick as can be. In highest gear it takes about 40 easy turns of the pedals to drive the ram all the way from one end to the other. In low gear it’s not too hard to achieve 1500 psi, which is probably a good operating pressure for what we want to do. By the feel of it it wouldn’t be that hard to do 3000psi either, but either the pump or the valve has a relief that’s kicking in at about 1600. Before it was kicking in at 1000psi, and I turned the adjuster screw on the valve most of the way in to get the 1600, so I suspect the pump (both are rated for 3ksi).
Brandon did a nice job on the assembly and it’s mostly dry though a few fittings on the valve assembly leak a bit at pressure – gotta torque some of them down further. I’ll wait until the whole system is assembled in the yard so I can make any layout modifications at the same time.