szrdave Posted November 6, 2020 Report Share Posted November 6, 2020 A couple of friends and I have a winter project to build a bike lift (each, obvs). Planning on using a single acting hydraulic ram, coupled with a 220v electric pump. We can adapt the hydraulic ram stroke and piston diameter to suit the pump, as long as we're in the ballpark in terms of max pressure (50-70MPa) and flow rate (1.5-2L/min). Something like this: https://www.ebay.co.uk/itm/7L-Hydraulikaggregat-Hydraulik-Pumpe-750W-Hydraulic-Pump-Elektrohydraulikpumpe/353255287014?hash=item523fa7e8e6:g:5SsAAOSwMNhe4FUY With a budget of up to 200 quid per pump we're looking at no-name eBay/Amazon stuff with limited warranty and even less spares backup, someone have a recommendation for a particular pump or supplier? Quote Link to comment Share on other sites More sharing options...
Damnthistinleg Posted November 6, 2020 Report Share Posted November 6, 2020 (edited) A 750 watt motor just to lift a bike 3 feet in the air over 20 seconds or so? Without doing any calculations it sounds surprisingly high. Is it possible to use a lower-powered, more compact and cheaper pump? Edited November 6, 2020 by Damnthistinleg Quote Link to comment Share on other sites More sharing options...
szrdave Posted November 7, 2020 Author Report Share Posted November 7, 2020 The force ratio lifting from closing is surprisingly high, too high in the current design actually as most hydraulic rams have a max operating pressure of about 20MPa. We can reduce the required pressure by increasing the ram stroke/increasing the piston diameter/increasing the minimum lift height, but still need a low flow high pressure pump. 10 hours ago, Damnthistinleg said: Is it possible to use a lower-powered, more compact and cheaper pump? Got a link? 😁 Quote Link to comment Share on other sites More sharing options...
Damnthistinleg Posted November 7, 2020 Report Share Posted November 7, 2020 That's the issue with these things. The requirement to have a minimal starting height is a pain when you really want the clearance to have a decent mechanical advantage at the start of the lifting stroke. I've had a back-burner plan to build such a bench for years but I recently ended up buying a second hand one instead. I did have one design in my head which used either a hydraulic ram or a motor which pulled a buttress thread through a fixed but rotating nut. Whichever linear-acting unit chosen then pulled on a chain which was connected to a 90 degree spiral sprocket that was fixed to the transverse, rotating lifting shaft, which in turn was attached to the main lifting arms. The effective sprocket radius changed over its rotation at a rate which was inversely proportional to the effort required. I never got beyond the basic idea but I don't see why it wouldn't work quite well. The small hydraulic units I had in mind were those all-in-one motor and ram jobbies that get used on tail-lifts, wheelchair lifts and other relatively low-effort things. They're only a couple of hundred watts at best but are capable of lifting some pretty hefty items over the sorts of distances you are looking at, in what is a similar time frame. The 12 volt motor would also allow for a rechargeable, battery-powered bench - something I reckon would be quite a nice feature in a workshop and there's plenty of compact deep-cycle AGM batteries out there that would be ideal for the task. It's definitely worth getting your lever ratios as close to linear as possible if you can as it keeps the prime mover small and compact. One of things I hate about many of these cheap hydraulic benches is the non-linear rate which becomes very apparent when you are lowering the bench. It's much nicer to have something that is easy to control. I'll see if I can find a link to the sort of hydraulic unit I was thinking about. Quote Link to comment Share on other sites More sharing options...
426hemi Posted November 7, 2020 Report Share Posted November 7, 2020 Automotech who I bought my ramp off sell the whole pump assembly separately and all parts. Quote Link to comment Share on other sites More sharing options...
Damnthistinleg Posted November 7, 2020 Report Share Posted November 7, 2020 Here you go, something along these lines..... https://www.hydraproducts.co.uk/Hydraulic-Power-Packs/Micro-Power-Pack Quote Link to comment Share on other sites More sharing options...
coombehouse Posted November 10, 2020 Report Share Posted November 10, 2020 I made a bike lift a long time ago. I used to use a trolley jack to lift it which was ok but not ideal. I found someone on eBay selling the air powered hydraulic ram that sealey use on their mc365a bench. The air motor pumps the ram & it works perfectly. Cost £40. Haven't seen them on eBay for a while but I haven't been looking for one. Quote Link to comment Share on other sites More sharing options...
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