Lego Hydraulics

[efferman]

grindinggears, you are right. New cylinders are working perfect. i have made a little comparisation vid

[Dutch_EE]

The hole issue of leaking cylinders is also known to me.

I've got the old pneumatic digger 8459, with air tank. Every time I tell the system the retract a cylinder I lose (almost) all of my air from the air tank. The high pressure air just leaks out with a lot of hissing and the cilynder hardly retracks.

Is there a way to repair such cylinders, or are they no longer usefull ?

Edited February 13, 2011 by Dutch_EE

[efferman]

maybe you could try rubber care lotion. in the most times it is grease, sometimes oil. i couldnt give a guarantee, but a try it is worth. normaly is a defective seal, forever defective

[rien]

thnx for the testing and sharing!!

gone use it sometime for sure!

[grindinggears]

Remember tho increasing the number of pumps will not increase the pressure, but it should increase the speed. Putting more rubber bands on the pessure regulator will increase the pressure. In fact, using a large cylinder as the regulator means the amount of resistance you put against it there will be the amount of power the hydraulics will operate at. If you have 4 kgs of spring pressure the cylinder should lift about 4 kgs. Alternatively you could use a small cylinder as the regulator. I believe it's pressure area to be about 1/4 the size of the large cylinder. This means that putting 1 kg of pressure there will translate to 4 kgs at the hydraulic cylinder, not accounting for the switch stiction.

I have done further tests this morning with increased water pressure.

I have attached more rubberbands to the pressure valve cylinder. When I hang a 4.8 kg weight on it the piston gets pulled out by nearly 1 cm now. 1 cm is the travel that is needed to open the pressure valve so theoretically every cylinder could now build up a pressure of 4.8 kg which should be sufficient compared to the ~4kg max load a LA can move

The pressure valve cylinder is an old one and I noticed that at this pressure the inner seal leaked a bit, water dropped out of the top hole. I have to replace that one with a 2010 cylinder.

The Motor struggles to build up the pressure for opening the pressure valve for the first time. After helping it a bit it worked fine but I have to solve that problem by gearing it down or using less pressure.

The increased pressure made the old pneumatic hoses pop off. The new ones from 8049 cope with the pressure perfectly.

Maybe someone else can do a bigger version of that system? I am at my limits because I only have 2 cylinders from 2010 and one pump

[Dutch_EE]

This means that putting 1 kg of pressure there will translate to 4 kgs at the hydraulic cylinder

But also I means that the small cylinder has to travel 4 time further ! That's the reason the power is equal.

Pressure = Force / Area

Energy = Pressure x Area x Travel

= Force x Travel

If you decrease the area of the piston by using a small cylinder, you can get away by using a smaller force if you travel 4 times longer, if you assume that the pressure inside the hydraulic system is constant.

[allanp]

But also I means that the small cylinder has to travel 4 time further ! That's the reason the power is equal.

Pressure = Force / Area

Energy = Pressure x Area x Travel

= Force x Travel

If you decrease the area of the piston by using a small cylinder, you can get away by using a smaller force if you travel 4 times longer, if you assume that the pressure inside the hydraulic system is constant.

I see where you are coming from, but I think you may have misunderstood me a little bit.

I was refering to the cylinder used for pressure regulation. If you use a smaller cylinder, the smaller one has a surface area about 1/4 the size of the larger cylinder. This means that the pressure would have to be 4 times as great before the cylinder can overcome the spring/rubber bands and move the valve, giving you four times more pressure. So I would advice using less resistance at first. But like I said, I don't know what kind of pressures are happening here so I can't say for certain that the pneumatic parts will cope.

[DLuders]

The Lego Education Store sells 6cc Syringes for Hydraulics (for all of you Lego Technic addicts out there! ) "Syringes are an excellent way to incorporate hydraulic or pneumatic power into your machine! Connected with tubing, syringes can activate arms, levers, grippers, and more. By combining large and small syringes in the same system, you gain mechanical advantage." You can also get Flexible Tubing from them. If the Lego Education Store sells these, are they "close enough" for the "Lego Purists" out there?

You could do what Scorge120 did on this

. If you did not want to operate the syringes by hand, make a Lego Technic mechanism that holds the syringe in place and moves the shaft handle up and down.

Edited February 13, 2011 by DLuders

[grindinggears]

@DLuders

The syringes have bigger holes and the tubing has an inner diameter of 3.175 mm which would allow greater speeds of the hydraulics.

But I don't see why this should be more appealing to a purist than our equivalent (see number 2 in the very first post, there is NO non-Lego part used apart from water)

@AllanP

I don't have a small cylinder to test your thesis and it is hard to get one that is new enough to have watertight seals. Maybe I'll get the Unimog this summer then I can try

Maybe even a purist can appreciate our hydraulic solution.

Until now I have not used any non-Lego items apart from the fluid containment. Using liquid instead of air is not a modification, it simply is using a part in a way that is not obvious at first. Think of the new helicopter 8068 that uses a wheel cover as a propeller. We use a pneumatic cylinder as a hydraulic cylinder.

Most important is: You can take the water out of the cylinder and wait a few days until it is completely dry if you are tired of hydraulics. Then it is a pneumatic cylinder again!

I know there was a (dutch?) shop selling pneumatic tubing and custom trainwheels. Does anybody remember its name?

[allanp]

@AllanP

I don't have a small cylinder to test your thesis and it is hard to get one that is new enough to have watertight seals. Maybe I'll get the Unimog this summer then I can try

I guess you don't need a small cylinder, you could try leverage. Put the cylinder close to the pivot point of a lever, then put the bands or spings far away from the pivot. This should require more pressure to activate the switch. But I can't emphisize enough to be mindful of the pressure damaging your one and only pump.

I have been doing some tests using tap water, a pump and a pressure gauge (that only goes up to 30 psi ).

Step one was to see how well it can pump air to compare later. It took 10 strokes to move the needle right round. So now that's sorted, time to pump water!

First of all I was surprised at how well it can pump water under pressure. It did it as well if not better than it does air. So next was to attatch the pressure guage. With four pumps it was the needle was right round touching the stop again on the other side, one more pump and the pipes (secured with a cross block) popped right off. But not wanting anyone to damage their parts I decided to go further and test the pump to destruction if necesary. So I kinked the hose and held the pipe on again with the cross block and also with my fingures as tight as I could. Again the pipe just popped off. Tried it several more times until a couple of times, the water forced it's way past the seal, pump going down but no water going anywhere. I figure this is gonna be the maximum pressure we're gonna get. It took a fair bit of force to push it down without pumping any water. Probably about 2 or 3 kgs at a guess (which means if the seals in the larger cylinder can take it, a force of 8-12 kgs may be possible from them). Anyway, after pumping water at what I figure to be the highest possible pressure attainable from these pumps I pumped the pump a few times with air to dry it out and hooked up the pressure gauge again to see how well it still pumped air. Thankfully it still works fine. Can move the needle of the gauge right round just as it did before with the same number of strokes as it took before (10 using air).

So it would seem that those little pumps can not only pump water as well as they can pump air, but it is also pretty hard to damage them by using them to pump water, at least for now I have failed to do so. Is there any other tests anyone would like me to do before we can say it's safe to use pumps in this way?

[efferman]

today i had take a look of the hydraulics from my steering system and get a shock.

The piston rod have a hole in the chrome. now i have no concerns, water is no good fluid for hydraulics with Lego parts. and now i have a problem. four cylinders and my steering concept are ready for the junkyard.

[grindinggears]

Uh, that looks bad.

Did you use tap water all the time?

I use distilled water with a little bit of alcohol like Timo suggested.

We'll see how mine will turn out, I am afraid yours cannot be repaired or does anyone have a solution?

[efferman]

i have used simple drinking water. i wish you much luck with your destilled water/alcohol composite, but i think you will get the same problem.

[Alasdair Ryan]

Perhaps we could change the water to something else,i dont know what though i am sure there is something better than water ou there.

[efferman]

maybe a low resistance RC shock absorber damping fluid would work, but my carpet would not like a leak in the system

[Brickend]

Were they left filled with water for a while?

I guess it stands to reason that Lego didn't use a metal with the rust resistance properties required for such operation.

[efferman]

well, sometimes a little amount of people must risk their parts, to let the community go forward. now it is clear that pure water is the wrong way for a longer use.

[Crtlego]

I am interested in building a fire truck with a working cannon that can spray water over large distances so I started looking at various posts on Eurobricks to find any posts on the use of Lego pumps in pumping water from a water bottle. I was able to find some posts that I am still going through but as soon as I saw the rust on efferman's pump I began to worry that the same would happen should I use water in my fire truck. Would such a thing occur in this situation?

[Nazgarot]

Hi,

I haven't had time to read the entire discussion in detail, but I did some research into the topic back in the darkages.

This part [4692, Pneumatic Distribution Block 2 x 4 with Non-return Valve] can be used to make a suction system that can use an old style pump to suck liquid into a pneumatic system. The problem is managing to fill the entire system with liquid without getting air bobbles. The pump should of course be possible to motorize, but i haven't tried how this is working with newer pneumatic parts. I believe the old style pumps both sucked and pumped, and the pneumatic distribution block was used to choose between suction and pressure.

To realize this system you would need a reservoir with a liquid (I would use thin silicone oil). One tube should be connected between the reservoir and the suction part of the distribution block, one between the pump and the distribution block, and one between the pressure output of the distribution block and the "hydraulic system" of modern pneumatic parts.

When filling the system it would be important to remember that one side of the modern cylinders has pressure and the other suction. This means that the whole system must be filled with liquid and aired before use.

4692

4701c01

Hope this was helpful.

-ED-

EDIT: Silicone oil for RC at 100 wt or lower weight should work fine. I would use one as light as possible.

Edited July 17, 2011 by Nazgarot

[allanp]

The pumps in this thread work well for pumping water at high pressure but at a slow, controllable flow rate for hydraulics. I would think that for a fire truck you would want something with a faster flow rate, so you can squirt water across the room . Seeing as a centrifugal pump would probably be impractical in lego, what about something like this:

Step one, fill the water tank by submerging the pump in water and selecting position 1 on valve 1. Keep going until water starts to pour out the outlet and then stop. BTW it is important for this outlet to be coming out the bottom of the tank.

Step two, fill the air tank with compressed air by removing the pump from any water and selecting posistion 2 on valve 1. Once pressurised return valve 1 to the central position.

Step three, now that the system is primed and ready for action, drive the fire truck to the fire by pushing it fast along the floor whilst making screeching noises! Aim the hose at the fire and select position 1 on valve 2. IIIFFFFF my thinking is correct, this should pressurise the water in the water tank forcing it out the nozzle at high speed.

Hope this help, and works!

Edited July 17, 2011 by allanp

[codefox421]

Has there been any more research done on LEGO hydraulics?

I'm wondering if Timo's mobile crane avoided corrosion by exposing only the lower half of the cylinder (away from the piston rod) to the liquid. If forced to use only one inlet, would such a system perform well enough for the intended applications? (I mainly wonder this because it would rely on negative pressure to retract the remote cylinder.)

Would love to hear further thoughts on this topic or try it out myself, but I'm afraid to lose the only cylinders I own. They also happen to be of the leaky variety, which is a bummer, but might be solved by only introducing liquid to the bottom halves.

[DrJB]

Hydraulics and Pneumatics are not the same. My recollection is that, one of the main differences between circuitry for the two is that, for hydraulics, one needs to provide a return path for the fluid. For air however, one simply vents air out.

Edited September 19, 2013 by DrJB

[Rockbrick]

as we can see water, though not compressible, is no good to the metal parts

then you have to be careful what oil to use as certain oils will be no good to the rubber seals....

using something like green LHM from citroën Hydraulics - needs special seals that are made for that oil

the tops of the cyclinders need tighter seals to stop/reduce leakage, the whole system needs to be free from air, so self bleeding and definately pressure regulated and all the ends would need little clips to stop them popping off

[codefox421]

one of the main differences between circuitry for the two is that, for hydraulics, one needs to provide a return path for the fluid. For air however, one simply vents air out.

the whole system needs to be free from air, so self bleeding and definately pressure regulated and all the ends would need little clips to stop them popping off

Let's assume we don't need to worry about the lines popping off (it's been said using tubing with a smaller inner diameter could solve that).

Using hose with a smaller inner is a great idea, and so are his others. Makes me think it could work.

Would a closed system work well enough?

It is obvious a closed system works. See this video of one (at ~1min):

grindinggears, you are right. New cylinders are working perfect. i have made a little comparisation vid

However, my thoughts are along the lines of using only one hydraulic line between the cylinders, like so:

It's clear that this setup does actually work...

Here's the closest thing I could find on the net to a video of hydraulics made from lego pneumatics. Doesn't really show much but here it is anyway.

...but I wonder if this would solve the corrosion issue and perform well enough to suffice. Any thoughts?

[Blakbird]

Hydraulics and Pneumatics are not the same. My recollection is that, one of the main differences between circuitry for the two is that, for hydraulics, one needs to provide a return path for the fluid. For air however, one simply vents air out.

Every fluid system needs a return path. However, with LEGO pneumatic systems the return path happens to be the atmosphere which is also the reservoir. Provided that your hydraulic system was immersed in an oil atmosphere, you could do the same thing.