Lego Hydraulics

[allanp]

All you really need to do to have a closed circuit is have the valves either submerged or directly above the tank so that the fluid goes back into the tank, and have the pump submerged in the tank, with drive axles going down to the pump and valves.

Edited September 19, 2013 by allanp

[Saberwing40k]

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?

Actually, you could totally do this, as explained in a book on robotics I got a while ago. You simply use the compressor to raise air pressure in the bottle, which forces the water out. Alternatively, you might be able to use this pump:

I've personally tried using water with mine, and brick built hydraulic cylinders, and I've never encountered a problem.

Or, you could in theory use these tubes:

And some kind of impeller pump to make the fire truck work.

[Rockbrick]

Closed systems would be tricky as there is always seepage

Inagree You would need a reservoir to contain the pump inside (covering the holes of the pump and accumulator/reservoir)

This would ensure no air goes into the system and the system if it remains pressurised would not let air in any of the joints or connections...

[allanp]

Closed systems would be tricky as there is always seepage

Inagree You would need a reservoir to contain the pump inside (covering the holes of the pump and accumulator/reservoir)

This would ensure no air goes into the system and the system if it remains pressurised would not let air in any of the joints or connections...

That's the idea! I have tested motor pumps (the older, shorter version) and when they are submerged they seem to pump water just as effectively as pumping air and I wasn't able to damage one by doing so.

[codefox421]

That's the idea! I have tested motor pumps (the older, shorter version) and when they are submerged they seem to pump water just as effectively as pumping air and I wasn't able to damage one by doing so.

Do the small cylinders and pumps (x189c01 and x191c01) have any metal components in them? I would guess not based on pictures of them, but I don't own any, so I can't check. If they don't, it would make sense that they can't be damaged by corrosion.

[allanp]

No they don't, however it's a 1:1 ratio, so just one pump of the....um...pump...will give you the full extention of the cylinder.

[dhruv]

cool idea of the brick-built cylinders

[darsedz]

The simplest idea to do a good working hydraulic pomp is usage of double side acting cylinder and two valves with control depended on direction of piston movements. One of valves will be responsible to switch direction of flow from tank (to suction side of cylinder), second valve will change a flow from active cylinder chamber to an output (as pomp output).

To increase volume efficiency system like “boxer engine” will be used. Max pressure will be limited by max force on cylinder road and it area of active piston side. Maybe additional air tank will help to “stabilize a flow pulses”. Bigger pumps (3-5 cylinders) will be designed as like “stars structures”, min. section of holes in a system will limit a max flow.

Similar method with double side cylinders and two valves can be used on actuators.

I don’t have experiences in LEGO pneumatic systems, idea is based on 15 years experience in industrial pneumatics and hydraulics (servo control as well)

[Rockbrick]

if you use a double side acting cylinder as the source of the pumping - you'd need a one way valve somewhere to stop the opposite chamber sucking while the other one is pushing

[darsedz]

Yes, as I mentioned - we need two valves for control of direction of flow from and into the cylinder. Valves must be switched on endpoint of cylinder.

The Lego valves looks like 3/2 type vales (3 way, 2 positions).

Some concept of "mechanical" part shown below, without a pneumatic elements (LDD don't have it), so some of dimensions will be different.

Two cylinders working in opposite directions, driving by 2 gears (maybe smaller?) and electric motor. Valves switched both simultanously by traveling pins on gears.

I'm not sure about leakage, but it's depends to fluid used in the system, I suggest hydraulic oil, maybe low viscosity, but this really needs a tests. I'm thinking on ordering thouse elements it and do some tests. We have also some test equipment (pressure / flow sensors and amplifiers) so some test on field can be done, if concept will work ;)

The same principle can be realized by 4 check valves (but LEGO don’t have it) connected similar to "Greatz bridge", such installation will work "automatically" (in our laboratory we have installation with 3 or 5 cylinders, working as a pomp for small hydro power plant, driving hydraulic motor and generator).

[DrJB]

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.

Seems it's getting a bit 'pilosophical' here which is alright. My point was that, for hydraulic systems, the fluid MUST be returned to a 'reservoir'. For air however (the way bus doors operate), the air can be simply vented out. Yes, I agree that in essence, the outside air (atmosphere) IS the reservoir ... though we might as well invoke principles from Thermo-Fluids and continuum mechanics ... Would be an interesting debate for sure.

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.

Strictly Speaking ...

Work = Force x Travel

Though for sure, Work and Energy have the SAME physical units, and thus the terminology is sometimes obscured.

[allanp]

Yes, as I mentioned - we need two valves for control of direction of flow from and into the cylinder. Valves must be switched on endpoint of cylinder.

The Lego valves looks like 3/2 type vales (3 way, 2 positions).

Some concept of "mechanical" part shown below, without a pneumatic elements (LDD don't have it), so some of dimensions will be different.

Two cylinders working in opposite directions, driving by 2 gears (maybe smaller?) and electric motor. Valves switched both simultanously by traveling pins on gears.

I'm not sure about leakage, but it's depends to fluid used in the system, I suggest hydraulic oil, maybe low viscosity, but this really needs a tests. I'm thinking on ordering thouse elements it and do some tests. We have also some test equipment (pressure / flow sensors and amplifiers) so some test on field can be done, if concept will work ;)

The same principle can be realized by 4 check valves (but LEGO don’t have it) connected similar to "Greatz bridge", such installation will work "automatically" (in our laboratory we have installation with 3 or 5 cylinders, working as a pomp for small hydro power plant, driving hydraulic motor and generator).

Wouldn't having a motor pump submerged in the tank be simpler?

[darsedz]

yes, maybe, but...

1. we need a tank, able to accommodate pumps (Lego don’t have it, need gluing bricks)
   
2. if tank is open = dust, dirt liquid, splashes….
   

My proposal it’s a closed system, ready to implementation and expansion or modification (cylinders selected depends on system needs), system easy implementable into vehicle, with fluid not exposed to environment…

[allanp]

Oh right, in that case I guess you could use lego airtanks for a tank.

[Rockbrick]

The air-tank would be a pressure accumulator - not a 'reservoir' to store the fluid

Oh right, in that case I guess you could use lego airtanks for a tank.

[darsedz]

Lego Air tank has two inputs, thus can be used as oil tank or accumulator.

The tank requires leaving one entrance open, facing upwards. Through this output container will be able to "breathe", to compensate for lack of oil - by the air from the atmosphere. Remember volume of oil in cylinder changes, in relase to position of piston,

From min_vol = stroke * (Area_piston - Area_rod) to max_vol = stroke * Area_piston

Level of oil in tank depends of actual configuration of pistons.

Airtank (working as accumulator), placed behind "pump" will help to "stabilize" flow. Of course, to do that some amount of air must be inside of accumulator (like on standard hydraulic gas accumulators).

I'm really thinking to test that, in real devices, just to have more practice... but it requires investmens ;)

update... Stuff ordered, without airtank (it's expensive and rare)... so tests soon ...;)

Edited September 27, 2013 by darsedz

[Boxerlego]

A couple of months ago I started a thread about Hydraulics and gave some of my thoughts about it. Now I want to show you some of the parts. In Lego Scale! :laugh:

This is the Hydraulic Gear Pump. It is powered by a small DC Motor. The black gear has a notch that fits over the dc motor drive shaft.

Here is the accumulator. This is device that will pressurize the system. Note: that the tubing can fit easily right in the Technic hole.

[darsedz]

I also finished some first attempts, but it's disappoints me. Lego valve need a rather lot of torque to switch it and I thinking on usage some simple self-made check valves instead of. It’s non Lego solution but…maybe enough to start thinking on rest of circuit.

[pmichiel]

I'd be reluctant to use water, I very much suspect the pistons will start to rust eventually.

I'm not sure what kind of washers are used inside the pneumatic pistons, but if they're rubber based then you need to stay away from vegetable oils as well as they contain acids which will ruin them.

Probably best to use a mineral oil, which is what real hydraulic fluids usually are.

[darsedz]

I want to use oil for hydraulic systems,maybe some low viscosity oil, actually I'm looking for it

[Lego Otaku]

mineral oil is fairly low viscosity and it won't rot or stink like other low viscosity oil (mostly cooking oils)

[Rockbrick]

Mineral oil needs compatible seals it will still rot the wrong rubber - not corrosive if spilled so the best choice for this situation

Canola oil too has excellent viscousity

[Lego Otaku]

Canola is organic and will rot like food, making stink if it leaks. I don't know if it retains viscosity or if it changes over time due to age.

[Rockbrick]

you'd need to add an antioxidant to keep it from going off but something cheap and replaceable as canola oil should only be a problem if you leave it in the system for years

in industry they use Butylhydroxytoluene (BHT) - a well know anti-oxidant that had been used for years in the manufacturing industry as an anti-oxidant in many products, including food and food packaging

[Boxerlego]

Probably best to use a mineral oil, which is what real hydraulic fluids usually are.

I agree mineral oil is the best but you have to be careful as to what mineral oil your going to use because some mineral oils out there have perfume in it and that will ruin the ABS plastic /Lego. Here is a great video about mineral oil.