regards hydraulic circuits, can you do the following

[scott33]

New here, hello, a google on my topic brought up hydromech's thread here somewhere. hydromech seemed the right person for the job. I would like to know if you could have the following hydraulic setup.

A 10-15mm diam and say 100mm long cyclinder and piston (piston 1, lever A) provide pressure like say a motorcycle levered hydraulic brake circuit.

The exit pressure/fluid line is a tube exiting perpindicular to the said cylinder. At the other end of the cylinder, opposite end to the the levered piston, is another piston 2, its lighter spring loaded function is fluid pressure release/moderation.

So I'm imagining in response to force on the lever A which pushes the piston 1, there is then an exit pressure which climbs and then plateaus (as piston 2 retracts in response to pressure).

The force on the piston 1, from the lever A, is spring resisted, but this lever, if given enough force, will move sufficiently to mechanically (via more levers ...'B') exert negative pressure on the pressurised circuit. (say this levers B system connects to a piston 3, acting on the cicuit)

So the system is imagined to have an exit pressure, in response to increasing input lever pressure, that initially increases in pressure, plateaus, and then drops off to zero .

I imagine it compact, which is why try to have one cyclinder providing two components to minimise weight and space, If it weighed a lot more more than say a motorcycle brake front brake reservior it wouldn't be so viable.

Apart from it being potentially completely unworkable (I dont know)

Any thoughts on that very much appreciated, not sure if I should continue to imagine this one or not.

Thanks
Scott.

 

[desertfox]

hi scott33

The offset forces will occur on the beam due to spring 1 and spring 3 which will tend to bend the beam and rod connected to piston 1, the fact you apply the resultant load there to keep piston 1 moving forward won't make any difference.
Now at present according to the sketch the only bearing support you have is through the top of the cylinder,even if you place an 'o'ring round piston 1, because the seal can compress it won't prevent twist due to the other loads on the beam.
So your bearing length through the top of the vessel is very short and any twist will increase friction and thus an increased thrust load.
Badly worded by me, I meant the seal on the rod of piston 1 should be mounted in the top of the vessel statically so that as the rod travels forward it rubs the seal along its travel.
Now a further point if the whole device including the brake caliper as a fixed amount of fluid (which I think you mentioned in an earlier post), then what happens when the swept volume of piston 3 is greater than that of piston 1 and 2, it suggests to me that without a fluid resevoir that you will have a void.
Note also that if piston 2 and 3 are not fitted with seals, then fluid can run behind both pistons, which means there not pressure tight and the whole device will fill up initially and not work.
Also how are you going to fix the stops inside the cylinders for pistons 2 and 3, I am struggling to see how you weld or fit the stops without splitting the cylinders.
Imagine now that piston 2 is just a solid end,why can't piston 1 on its own pressurise the fluid and piston 3 just be the relief valve when piston 1 travels to far using the beam.
Perhaps I am missing something but do you really need piston 2.

desertfox

 

[scott33]

Do I need piston 2?! - of course I need piston 2, that's heretical talk .....I mean it...it....its piston 2 .... best idea I have heard today. I think you are right (although having had only one coffee it's hard to be sure )

so if piston 2 is gone then spring 3 / piston 3 took the function of spring 2 / piston 2...and yet its (big pressure drop) function due to the displacement derived from its connection to lever 1 remains intact...far as I can tell. How about that!

Your thoughts on manufacturability can only be appreciated when my caffeine deffiency has been attended to.

meantime thanks again desertfox.

 

[desertfox]

Hi scott33

Well if the caffine don't work, let me know I'll put some diagrams up about the bearing lengths etc.


desertfox

 

[scott33]

Hi desertfox, sheesh its hard to access the interweb, with wannabe youtube addicts (read my kids) around.

Anyhow, regards the few things I can understand, (and your diagram would be, I suspect, a great help ...given time and inclination... )

About formation of a void - my inclination is to avoid a reservoir, (not sure how realistic or theoretically possible that is) since the utlity of the design is decreased with increasing space and or weight.

I imagine that the effect of the displacement of piston 3 due to the rod (being contacted by lever 1 in the last period of lever 1 movement) will be to return the volume of the system to that of the start state. (And the remote brake calliper - which is acting in response to this systems exit pressure will simply need then to be off.)

I guess that is a fine point to judge (ie calculate and manufacture to a fine spec). If voids make for non reversing cavitation or some such it is problematic, if voids do nothing other than be voids perhaps it is ok...??

Fixing the stops, far as I see there's only one in the design now (for piston 3)... imagining the book - "Hydraulic Circuit Design Essentials" and the chapter 'Stop Design' and subsection 'Manufacturing Considerations'... just can't quite read what it says...;-) Something like 'Be sure your design is buildable' - well seriosuly I can't quite picture what may be required.

The gist I guess is to figure out how to make it as seperate buildable and thread togetherable components and ... thread them together.

Your diagram would be a cool breeze - it's high summer here.

Thanks again desertfox.
Scott.