Pneumatic Cylinder Disassembly & Lubrication Findings

[Costas]

I have a number of old & new pneumatic cylinders that I wanted to improve in regards to smoothness and overall performance.

The standard lubrication seems to work OK but I found that smoothness & performance can be improved by selecting a suitable replacement lube.

 

Note that no physical modification was done to the cylinders apart from substituting the lube used.

Tests were to be done with and without a working model to see what effect the various lubes had. Model I had readily available was the Custom Bricks - Grubber kitted out with my 42054. - See vid below (not my video)

 

 

First step was to disassemble a number of cylinders so that I could I try a couple of different lubricants to see what effect they would have Vs the stock lubricant LEGO use.

To de-grease the cylinders thoroughly and without causing any damage to the plastic or rubber and silicon components I chose to use an electronic component cleaning solvent.

These are generally safe for use on the majority of plastics, rubber and silicon parts as the solvent needs to be safe for many electronic components which also use these materials.

 

Once de-greased, the cylinders were ready for the replacement lube.

A small snapshot of some of the cylinders which I was testing.

 

 

Closeup of 19475c01

 

 

Closeups of 2793c01

 

 

 

Closeups of 47224c01

 

 

 

Closeups of 19467c01

 

 

 

Initial test was with 80 weight silicon oil - I had high hopes for this as the oil is very 'slippery' and I thought it would act as an excellent lube for the cylinders.

What I did not count on was that it actually caused 'stiction' issues whenever piston movement stopped and restarted which caused very jerky operation.

Not only that - overall pressure/performance was also reduced possibly due to small amounts of blow-by leakage around the seals.

So the silicon oil was actually quite a disappointment and I would not recommend it as an internal lube for these cylinders.

What I found the silicon oil good for is using at as lubricant for pneumatic pumps as these operate at moderate rpm's where the oil seems to work better than grease.

Edited June 22, 2019 by Costas

[Costas]

Since the oil was such a let down, I decided to switch to a grease.

My list of greases were all silicon based derivatives mainly so that they would be reasonably inert with respect to the materials used by LEGO.

Some people have tried Lithium based greases in the past with some success but many of these are of a lower viscosity than some of the other options I was looking at.

 

I started with a silicon grease which I use on my pool pump O-rings. This seemed to work OK, but if anything it still seemed that it was too low a viscosity for the application - so while piston operation was smooth, the pistons would operate far too quickly as not much damping effect was noticed.

Piston damping performance is important as if it is too low, the pistons operate way too fast and it becomes very difficult to smoothly control a function with the valves ie. arm or bucket under control of the pneumatics will all too easily snap to full deflection. For me this was an important variable to get correct.

 

Next I tried a silicon dielectric grease which had improved viscosity over the pool pump O-ring grease and this worked better.

So next I started to look on-line for a better alternative and came across the following product:

 

DOW Corning's - Molykote 111

This grease seemed to have higher viscosity again (designed for certain damping applications) and was a silicon product that is designed to be utilised with most plastics/rubbers etc and is also approved for use in food environments, so not toxic.

I purchased a 100gm tube on line and it arrived the other day.

 

 

I quickly cleaned and re-greased a couple of cylinders with Molykote 111 and put them to the test.

All I can say is that this product works extremely well and I was very impressed.

Piston performance is extremely smooth and the damping effect is great. It is very noticeable on heavy loads such as the Grubber's main arm as you can easily lower this heavy weight with reasonably good fine control using the pneumatic valve.

No longer do you have to play that tricky guessing game in trying to position the valve's lever in just that exact spot where moving it just 0.01mm results in the arm you are controlling to go full tilt in that one direction...!

 

I need to take a few photos of filling the cylinders with grease - Job for tomorrow maybe... :) 

I have not taken any photos of that process so far as I was reluctant to swap between assembling pistons/cylinders with grease, switching over to camera to take a few shots and then back to assembling and then trying to keep the grease off my camera & lens when in the rushed phases of trying to test all the grease combos.

Edited June 22, 2019 by Costas

[lcvisser]

Interesting work. I have a bunch of old cylinders that would benefit, but I'm hesitant to open them. If your video could also include some instructions on how to open the cylinders would be great.

I'm not sure if this product is readily available in Europe... A quick search only gave me a few shops on Amazon.

[Arnoob]

Ludo, no worries, Molykote is also available in the Netherlands:

http://Google search for Molykote 111

[Costas]

14 hours ago, Ludo Visser said:

Interesting work. I have a bunch of old cylinders that would benefit, but I'm hesitant to open them. If your video could also include some instructions on how to open the cylinders would be great.

I'm not sure if this product is readily available in Europe... A quick search only gave me a few shops on Amazon.

 

Check out this persons video which does a reasonable job in showing you how to disassemble them.

NOTE: NEVER drill out and modify the holes in your cylinders as shown in the video as this will destroy their overall performance for normal applications in our models. Enlarging the holes is only useful when using them for air powered engines as you need a very fast acting piston.

 

 

The small cylinders are easy - It is the larger ones which are a little harder to open but still reasonably easy to do.

I only use some basic jewellers type screwdrivers for the job - 2x 3mm flat blades and one smaller bladed driver (this one is simply used as a spacer to temporarily hold one side open.

 

**Note that my photos below show the cylinder top already removed, but you get the idea.

First step is to pry the black top in one of its lower corners with one of the larger flat blade drivers.

Once you catch the corner of the top you can work the driver in and move it around to where the yellow nipple is - sounds easy but you will find that the screwdriver will want to push itself out due to the force of the black top pushing down on it.

 

Next I insert the small screwdriver into the gap and this is used as this screwdriver will stay in place whereas the larger one will not stay in place while we open and work on the other side.

 

Now move over to the opposite side and insert one of the larger drivers and once this driver is positioned where the nipple is, try and hold it in place and then at the same time insert the other large driver back in where the smaller driver is holding the other side open.

Once both large drivers are in position - carefully move them outwards so that you flex the black top over the nipples - try and do this on both sides at the same time and you will find that the top will slide off. 

It is much easier to accomplish if you have 3 hands...

Once apart - they do go back together very easily which is a bonus.

Edited June 23, 2019 by Costas

[Costas]

A few tips on greasing the internals with Molykote 111:

Coat the inside of the cylinder with grease - I use about twice the amount shown to coat the inside of a long V2 cylinder.

 

Next - Apply a liberal coating over the piston shaft and pay particular attention the seals - Ensure that you fill in the small cavities on top and below the top rubber seal with grease as well as applying a heavy coat over the piston itself. Ensure that you fill in the gap formed by the two 'lips' on the outer circumference of the piston itself.

The grease provides two major functions here:

• First is the obvious lubrication ability
• Secondly (and in some cases the most important function) is that the grease assists in forming an airtight seal between the piston and more importantly between the top seal and the piston shaft.

Some people have experienced small air leaks when pneumatic cylinders have a reasonable amount of side loading applied. Usually this is because air will leak out between the top seal and the piston shaft.

This is a bit of a weak point in the design of the top sealing elements in these cylinders. Using a high viscosity grease here helps immensely in keeping an airtight seal between the shaft and the top seal.

 

 

Don't be afraid to go a bit heavy on the application as it will not hurt anything - We will eject the excess grease after re-assembly.

Once all done - reinsert the piston assembly back into the cylinder's main body and ensure the top seal is seated correctly before pressing home the top black cover.

Once reassembled you need to manually operate the cylinder to both extremities multiple times (a dozen or so).

Use some moderate force at both ends of travel to force out excess grease at the relevant port.

 

 

After a dozen or so goes the majority of excess grease will be ejected and the cylinder should now operate very smoothly.

Hook it up to a small pump and valve to test full functionality and you should be good to go.

I give my reworked cylinders a quick wipe over with a tissue moistened in some of the electronic component cleaning solvent to remove any left on grease etc.

[powerwindows83]

a little off topic, but it would be nice if TLG made air springs (airbags) like trucks have. just a short-throw high-volume flexible rubber accordion with a port on it

[Andman]

I had a discussion with a seller of tools, grease etc. I told him that I'm looking for a grease for my pneumatic cylinders. He recommended to use Molykote 55 o-ring, which is, according him, designed for moving parts in pneumatic systems, instead of Molykote 111. I tested it today. Before i had some no name silicon grease, which did not work well. The cylinder did not move smoothly at low pressures. That was solved by Molykote 55. The movement even with slowly increased pressure is very smooth. The issue is that this grease doesn't handle pressure applied to the rod very well. The air passes the rubber ring easily. The original grease withstands much more pressure. I'll order Molykote 111 soon and will post the results.

[allanp]

Looking forward to seeing your results 

[i really dont know]

I've been thinking about messing around with some grease in my pneumatic cylinders, in particular my small cylinders which have a lot of "sticktion" when operating which means they only work at higher pressures which is problematic. It sounds like the "sticktion" with the molykote 111 is pretty low? is that a correct assessment? Guess I'll have a look around and see if i can get my hands on some of that grease and try it out myself, I'll try to remember to report my results when i get around to it. :)

[Mikdun]

I also play a bit with Molykote 111.

I have two small cylinder that were a bit stubborn to move.   The disassembly went quite smooth, but I broke one clip   Still, after assembly it holds good enough.

One of the cylinders suns much better now - no sticking at the end of travel. The other has damage to the rod, so no miracles here.

 

I also had old pump, that stopped to pump (but otherwise run smoothly), so gave it a try. Opening was not so easy, I eventually damaged a bit the plastics (some screwdriver marks). After taking out the piston I saw this:

So the Molykote did not help much.   Anyone already tried to find suitable replacement? It's kind of medium-hard rubber. Pneumatic cylinders have the same internal diameter?

[DrJB]

On 7/9/2019 at 11:57 AM, powerwindows83 said:

a little off topic, but it would be nice if TLG made air springs (airbags) like trucks have. just a short-throw high-volume flexible rubber accordion with a port on it

Are you familiar with this this part?