Someone on another unrelated board asked about the availability of small hydraulic cylinders. What they wanted to do was make "remote" steering on a bicycle. Nobody could really offer any useful suggestions. I haven't seen anything really small enough to do that well in the surplus catalogs I've been browsing for years. The smallest ones I've ever seen were maybe around 1.5" bore and 10" stroke, that would be far too heavy for this use.
A couple days ago I got another catalog in the mail (Burden's surplus center) and in addition to the hydraulic cylinders they have a couple pages of "pen" pneumatic cylinders also. They're called "pen" I guess because they're about the size of a writing instrument--most have bores of under a half-inch, with strokes of only 4-6 inches and PSI limits of 100-250. The best thing is that most only cost a few dollars each.
I can't think of any time I've ever wanted a hydro cylinder off a dump truck bed, but I could easily imagine using some really tiny ones. I'd think I'd want the more-solid action of hydraulics though.... What would be the issues with using pneumatic cylinders as hydraulics?
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Difference between hydraulic/pneumatic cylinders?
The big thing would be the difference in working pressure. Air most likely would be under 200 PSI. Where a hydraulic cylinder would start around 2,500 PSI working pressure and go up to 10,000 PSI.
You wouldn't catch me using an air cylinder in a hydraulic system. Cylinder walls are to thin and seals won't take the pressure.
Richard W.
You wouldn't catch me using an air cylinder in a hydraulic system. Cylinder walls are to thin and seals won't take the pressure.
Richard W.
Doug4d3s
I would be interested in the engineering to remotely steer a bike. An air system is a hydraulic system with different characteristics. Air might be used, depending on steering data, to steer a bike. Air would, if usable in this situation, be cleaner and more user friendly than a liquid hydraulic unit.
Frank
I would be interested in the engineering to remotely steer a bike. An air system is a hydraulic system with different characteristics. Air might be used, depending on steering data, to steer a bike. Air would, if usable in this situation, be cleaner and more user friendly than a liquid hydraulic unit.
Frank
Well, I would figure that if you did want to use the little air cylinders for fluid, that you would not be able to drive them with any regular pump setup. It would be a hand-operated thing (another cylinder, pushed/pulled by hand) and you'd still probably want a PSI gauge in there and a adjustable relief valve.
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The (home-built) bicycle the other person wanted to use hydraulic steering for is a cargo bike called a bakfiets (a massacre of the Dutch term "bakfietsen" for them).
http://www.workcycles.com/home-products ... obike-long
Normally these bikes use a bent tie rod to connect the steering tube arm to one side of the fork. You can see it easily in that photo, painted orange.
The fellow wanted to build a folding bicycle like this--one that just has a flat rack up front (not a box) and that folded in half right ahead of the steering tube. So he wanted an easy way for the steering gear to fold along with the rest of the bike.
,,,,,,I don't think the pressures with a pneumatic-->hydraulic bicycle steering setup would really ever be that great. You can take any bicycle out there, brace the front wheel between your legs, and twist the handlebars left or right and the stem will slip on the steering tube. It doesn't take a whole lot of torque to steer a bike, even a MTB riding off-road. And a bakfiets is very much an on-road bike for certain.
It might be difficult for other reasons though. You would get leakage (so you'd need a reservoir) and you'd need a way to equalize the fluid on both sides of the cylinders.
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The (home-built) bicycle the other person wanted to use hydraulic steering for is a cargo bike called a bakfiets (a massacre of the Dutch term "bakfietsen" for them).
http://www.workcycles.com/home-products ... obike-long
Normally these bikes use a bent tie rod to connect the steering tube arm to one side of the fork. You can see it easily in that photo, painted orange.
The fellow wanted to build a folding bicycle like this--one that just has a flat rack up front (not a box) and that folded in half right ahead of the steering tube. So he wanted an easy way for the steering gear to fold along with the rest of the bike.
,,,,,,I don't think the pressures with a pneumatic-->hydraulic bicycle steering setup would really ever be that great. You can take any bicycle out there, brace the front wheel between your legs, and twist the handlebars left or right and the stem will slip on the steering tube. It doesn't take a whole lot of torque to steer a bike, even a MTB riding off-road. And a bakfiets is very much an on-road bike for certain.
It might be difficult for other reasons though. You would get leakage (so you'd need a reservoir) and you'd need a way to equalize the fluid on both sides of the cylinders.
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Last edited by Doug4d3s on Sun Mar 14, 2010 9:19 am, edited 2 times in total.
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Russ Hanscom
- Posts: 1955
- Joined: Wed Mar 15, 2006 11:10 pm
- Location: Farmington, NM
Consider the differences in the working fluid; one is compressible, the other is not (for practical purposes). Stop in mid stroke and the liquid unit will pretty much stay put, but the gas unit will act more like a shock asorber unless it is equiped with a fancy positioner. Up against the stops, they will pretty much act the same.
The choice of working fluid depends on what results you are looking for.
The choice of working fluid depends on what results you are looking for.
Right here are some inch bore cylinders... https://www.surpluscenter.com/sort.asp? ... yword=HCD1
bike steering
A long time ago I took 2 air cyclinders same size 1" x 10" hooked one end to the outboard 15hp and filled and bled the system one was the steering the other worked the motor. worked great, there was no mech. adv. because they were both the same size.
Gerald C.
Gerald C.
What I see here is a closed system not needing any kind of pump. Mechanical action on one end to move a cylinder and the fluid or air would move the cylinder on the other end completing the work desired. When you said "remotely driven" I thought of remote control instead of part of the hydraulic system movement at one location would move another part of the system remotely located. Sorry for the misunderstanding.
Gerald C has the right method. A cylinder attached to the steering and a cylinder attached to the wheel with two lines to each. Turning left one line is pressure and one is return. Turn right and the lines switch jobs. If a mechanical advantage is necessary, the steering cylinder would be larger (Power steering).
I believe at the pressures you are talking about, fluid could be used in air cylinders.
Frank
Gerald C has the right method. A cylinder attached to the steering and a cylinder attached to the wheel with two lines to each. Turning left one line is pressure and one is return. Turn right and the lines switch jobs. If a mechanical advantage is necessary, the steering cylinder would be larger (Power steering).
I believe at the pressures you are talking about, fluid could be used in air cylinders.
Frank
An air cylinder will not work progressively like a hyd. The pressure will build up until it overcomes the load, then the cyl. will operate through its full stroke, BAM. To have progressive action with air, you have to use a diaphragm setup, like a truck brake actuator. We ran into this years ago setting up an air-operated clutch on an oil field truck. A cylinder won't let you feather the clutch, it's in or out...
Air Verses Hyd Cylinder
Just some thoughts here;
Air has been used for over 100 years to operate valves and dampers by Johnson Controls and Honeywell just to mention a few companies that do it.
The differance is in how they do it. Take a Johnson Controls valve that works against 100 PSI head pressure. They can accurately stoke these valves from 0% flow to 100% flow by using 3-9 PSI of air pressure. (If that happens to be the spring control range)
Why this works is they use a large diaphragm (many times over the diameter of the valve plunger) with a spring on the backside that has a rating that matches the control air they will use. There is a large mechanical adavantage between the diaphragm area and the valve piston area so overcoming the 100 PSI of head is not an issue.
I suppose if you would apply the same principal you could steer a bike with air but the diaphragm size might be very hard to work with.
All the comments about using an air cylinder as you would a hydraulic cylinder are spot on. Not a very good application for air.
Dave C.
Air has been used for over 100 years to operate valves and dampers by Johnson Controls and Honeywell just to mention a few companies that do it.
The differance is in how they do it. Take a Johnson Controls valve that works against 100 PSI head pressure. They can accurately stoke these valves from 0% flow to 100% flow by using 3-9 PSI of air pressure. (If that happens to be the spring control range)
Why this works is they use a large diaphragm (many times over the diameter of the valve plunger) with a spring on the backside that has a rating that matches the control air they will use. There is a large mechanical adavantage between the diaphragm area and the valve piston area so overcoming the 100 PSI of head is not an issue.
I suppose if you would apply the same principal you could steer a bike with air but the diaphragm size might be very hard to work with.
All the comments about using an air cylinder as you would a hydraulic cylinder are spot on. Not a very good application for air.
Dave C.
I learn something new every day! Problem is I forget two.