Hydraulic Throttle Control?

Many many years ago I saw a dragster that used two small single action hydraulic cylinders of the same
bore for a throttle control. It was a real simple setup, all very low pressure as the cylinders simply
acted as a solid link between the pedal and injectors. There is was no multiplication of force simply one
small cylinder moving another of the same bore. If I remember one of them or maybe both had a compression return spring in it/them.
I'm building a Cyclekart with a 6.5 hp Honda GX-200 engine and would like to use a hydraulic link to the
throttle instead of the typical rod/cable or wire such as used on gokarts.
The part that has me in a tizzy is the O'-ring seal. the bore can be quite small such as .5" and the wall of the cylinder doesn't have to be thick because there is no pressure to speak of. I'm thinking a steel shaft fitted with an O-ring and O-ring seals at the end that has the assembly nut.
I'm drawing a blank as to the O-ring grove and clearances. The cylinder will probably be aluminum honed
to the correct size so the O-ring will seal.
Any Ideas or experience would be more than welcome.

Thanks
Denny Graham
Sandwich, IL

Why make it when pneumatics are all over the place.

From automation surplus there are many sizes cheap.

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Parker writes the bible.
Google Parker oring gland design.

I would buy a off the shelf pneumatic cylinder - they work fine for low pressure hydraulic applications.

Clippard is one popular brand - Clippard Minimatic SM 2 Sub Miniature Cylinder Lot of 2 | eBay

You need to think about this a bit more. It is inherently unsafe. Back in the 60's, a regulation came into force that required two cable throttles (push & pull) on motorcycles. Prior to that regulation, most motorcycles used pull only with spring return. There is no doubt in my mind that this twin cable regulation saved many lives, but this was for motorcycles, not other vehicles. Since then, many changes have taken place and today it is very common to control throttles with electronics, even on motorcycles. Personally, I find placing my life in the hands of a transistor frightening, but the same logic that forced the twin cable solution has not been carried forward by the authorities. Another reason to avoid hydraulics is response time. Keep in mind that spring tension must overcome flow restrictions to follow your foot. All of these risks are not necessary, your call.

Hi steve-I . . . I mean you no disrespect, but I have to take issue with some of your concerns. While I agree a push/pull cable has been a significant safety enhancement to motorcycles - I disagree with your rationale for your remaining assertions.

There are no appreciable time delays related to using hydraulics and a good many over the road rear engined vehicles use pneumatic throttle controls as do a great many marine and industrial vehicles . . . these pneumatic systems have delays that are orders of magnitude longer than any hydraulic system yet are still responsive enough to provide excellent throttle (and brake) control.

I wouldn't hesitate to use a hydraulic system for a throttle - (just as nearly 100% of all passenger vehicles use hydraulic brakes) . . . if hydraulics were unreliable, then the automotive industry wouldn't have switched from cables to hydraulics wholesale in the 1920' - 1930's.

Having worked on a car with a hydraulic throttle, a bodged up V8 Chevy powered tube chassis fake Lamborghini Countach I can say for sure I would not advise anyone to use a hydraulic throttle control. The problem with this thing was stiction in the cylinders. Stick / slip in anything to do with a throttle is not a good thing. Bleeding the thing is an additional unnecessary PITA. The car left the shop with a cable.

Every clutch I've had for the last 20 years has been hydraulic. Small cylinder on the pedal, bigger cylinder inside the bell housing. Just sayin'. Always worked fine for me.

mdshunk said:

Every clutch I've had for the last 20 years has been hydraulic. Small cylinder on the pedal, bigger cylinder inside the bell housing. Just sayin'. Always worked fine for me.

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Think about the springs in your average clutch, and then compare that with a throttle spring that is light enough to not tire out your leg, IE almost free running. Pretty easy to make a clutch work. Just sayin'. If I was going to try it I would set it up with double acting cylinders so it is hydraulic open and close, not hydraulic open, spring close like the fake Lambo. I worked on was. If it is so easy go for it, giver hell and let us know how it works for you.

A common brand of hydraulic controls for the marine industry is Hynautic and Heavy metal linked to an aftermarket automatic supplier.

Poorly designed installations shouldn't be used of examples of why this isn't workable. Generally marine designs are fixed position two way (push pull) designs while automotive solutions have a one way (push only) with a large spring in the slave cylinder to cause the throttle to return to idle position. The ratio of pedal to slave cylinder diameters along with proper sizing of the spring within the slave cylinder would obviate seal drag and resulting feel of "stickiness"

I have one of these levers in my shed but it is also warn and would hardly hold. I swopped it on my boat for Morse cables and control when I changed the manual LM100 box for a LH150.