Subject:
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Re: Pneumatic Cylinders
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Newsgroups:
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lugnet.technic
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Date:
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Sun, 4 Apr 2004 19:13:46 GMT
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Viewed:
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1671 times
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In lugnet.technic, Martin Bruun wrote:
> In lugnet.technic, Maggie Cambron wrote:
> > In lugnet.technic, Mark Bellis wrote:
> > > I've bought quite a few 8455 excavators now and in all of them the pneumatic
> > > cylinders have restricted air flow due to partially blocked nozzles. The amount
> > > of restriction varies, as measured by extending and contracting the cylinders by
> > > hand and feeling the amount of force required to move them quickly.
> > >
> > > So far I've used a 1.4mm screwdriver to bore out the nozzles so that air can
> > > flow faster. You do this at your own risk!
> > >
> > > I suppose the flow restriction helps the cylinders to move smoothly but I wanted
> > > them to move faster, particularly for doing logic functions when moving other
> > > switches, as it's better to move the switch all the way at once.
> > >
> > > Also, in a power application, such as lifting an arm, more source pressure is
> > > required to move a cylinder that has flow restrictions at the same rate as one
> > > that doesn't. It's a bit like friction within a motor. The consequence is more
> > > use of the hand pumps and then a need to release the excess pressure later.
> > > This, in addition to the balloon effect of rubber tubes, makes the system quite
> > > inefficient.
> > >
> > > Are the nozzles supposed to be restricted or not?
> > > Have you had the same problem?
> > > Would you recommend boring out the nozzles as I have?
> > >
> > > BTW where can I get a 100m reel of the thin tubing used for the flex system? I
> > > would cut this to length and use it for all the straight tubes in a model with
> > > rubber ones only for the corners, reducing the balloon effect to a minimum and
> > > increasing efficiency and speed by saving on the amount of air required to
> > > operate pneumatic models.
> > >
> > > Mark
> >
> > Hi Mark,
> >
> > Here is a post by Martin Bruun on the subject that may interest you:
> >
> > http://www.bricklink.com/message.asp?ID=38293
> >
> > I am recopying the text of the message here, as BrickLink only keeps posts for
> > six months and this information may be useful even though it was primarily
> > directed at sellers on BrickLink:
> >
> > "Just a piece of advice to those sellers (like myself) who part out the 8455
> > Back-Hoe. Please take the time and test your pneumatic pumps and cylinders. I
> > have found a large percentage of those to be defective. The problem with the
> > black pumps (found on 2 out of 7 tested) is that the non-return valve does not
> > shut the pump completely closed when the piston is either being retracted or is
> > just in the top position. This causes the pressure to escape the pneumatic
> > circuit whenever you retract the piston. The problem can be tested by connecting
> > the pump via a single piece of hose to the bottom inlet of a pneumatic cylinder.
> > If you pump so the piston of the cylinder goes up and
> > then try with your finger to press it down again, then it should be very hard.
> > If you can press down the piston without much resistance, then the pump is
> > defective!
> >
> > "The problem with the cylinders is simply that some of them move with a lot of
> > resistance (found of 4 out of 30 tested). It feels like one or both of the
> > inlets has too small airflow. They are not totally unuseable, but they are
> > definitely not working as supposed to. It is very easy to test, by simply
> > moving the piston in both directions with your fingers, you will immediately
> > feel the difference if you have a bad one.
> >
> > "I suggest that sellers state in the description field if their pumps/cylinders
> > are tested.
> >
> > Martin"
> >
> > So you are not the only one who has noticed problems.
> >
> > Maggie C.
>
> Yes, a shame that there isn't an archive of old messages on BrickLink.
>
> So here is a copy of a message I wrote after finding a solution to the problem
> with the yellow cylinder. (so it's not lost in cyberspace!)
>
> http://www.bricklink.com/message.asp?ID=41307
>
> After my original post I decided to sacrifice one of the yellow cylinders in the
> name of science.
>
> I actually got it opened without two much damage. The resistance seems to be
> caused by too much grease inside the cylinder below the piston. The grease
> builds up around the bottom inlet and prevents the free airflow. By removing the
> excess grease I managed to get the cylinder to work as good as any of the other
> cylinders. I then took one of the other cylinders and without opening it, I
> tried to make the passage free with a small piece of metal-wire. It actually
> improved the function to a degree where it no longer has noticeable more
> resistance than the ok ones.
>
> The black pumps is probably another question, but I had those replaced by TLC.
> The story about the odd number tested (7) is, that I had one defective in my own
> copy of this set making the pneumatic functions of the 8455 very slow and almost
> powerless. When I had identified the problem to be with one of the black pumps I
> called customer service, which quickly sent a replacement. I asked if they
> wanted the defective one returned, but no. However, the replacement pump
> suffered from the same problem. The next time I called customer service they
> were very interested in having the now two defective pumps returned, so they
> could examine them. my second replacement pump was
> ok and in my next two copies of the 8455 (parted out) there were no problems
> with the pumps (only with the cylinders).
>
> So the bottom line is, that if you have a yellow pneumatic cylinder with too
> much resistance then try with a piece of metalwire in the bottom inlet to make
> free passage. It might work.
>
> Martin
Thanks for the info guys. I have had one or two older pump cylinders that have
lost pressure. Also, some older yellow cylinders (with square bases) are
difficult to retract from the fully extended position, due to leakage in that
position. Consequently I decided to tweak the model design to not fully extend
them, especially when they are working as a push-pull pair. I have also retired
a few old switches due to leakage.
I tested the 8455 pump cylinders as follows:
1. press them with a finger over the nozzle, ensuring lots of resistance.
2. press them fast with a clear nozzle, ensuring no resistance.
3. release them from pressed position with a finger over the nozzle, ensuring no
effect on extension by the spring.
I test the 8455 yellow cylinders like this:
1. move them with a finger over the outlet nozzle, ensuring lots of resistance.
2. move them with a finger over the inlet nozzle, ensuring resistance, then
release and see how far the cylinder returns under vacuum.
3. repeat 1+2 for the other direction.
4. move them fast with both nozzles clear, ensuring no resistance. This is
where most of my 8455 cylinders have failed the test.
I have found that to get maximum performance out of the cylinders, both nozzles
of every cylinder need to be bored out with a tiny screwdriver. None of the
cylinders I have had in 8455s have had completely unblocked nozzles. Having
bored them out, performance is much enhanced in all cases and I can move them
fast in both directions, with no springback. Springback is due to a build-up of
vacuum, due to not enough air being able to get into the bottom nozzle when the
cylinder is extended fast, such that there is less air in the cylinder than the
volume swept, and unless you hold it extended, the cylinder will retract part
way as in test 2.
I checked out your info about the grease with my transparent cylinders from
ultimate builder sets. Yes, there is a build-up of grease below the piston.
When this is spread about by rotating the plunger as you extract and insert it,
the grease can be spread better. I think grease is responsible for the sticking
of cylinders after not being used for a while. However I don't think it's the
cause of the more permanent problem of slow airflow. You're right that a piece
of wire to remove grease from the bottom outlet will improve perfomance, but if
I look into the nozzles of 8455 cylinders I can see that the bore is restricted
by yellow plastic.
I think the improvement in performance given by boring out the nozzles proves
that that was the problem, rather than grease alone. Do any of your cylinders
have an apparently smaller bore within the nozzles?
Tell you what, boring out the nozzles on 100 cylinders gets boring! I usually
do a few when watching TV. Notice that the T-junctions have the same bore right
through, so cylinder nozzles should have the same.
With the problems I've had with the more complex Lego parts, I am resigned to
testing each one straight out of the box. At least I've not had to send
pneumatic parts back, unlike the motors (6!), but that's another story.
Mark
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Message has 1 Reply:
 | | Re: Pneumatic Cylinders
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| (...) You should also try with another cylinder to blow air into the pump while it is fully retracted (or being retracted). Otherwise your testing will not reveal a defective non-return valve. The air inflow in the pump through the nozzle should be (...) (21 years ago, 4-Apr-04, to lugnet.technic)
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Message is in Reply To:
| | Re: Pneumatic Cylinders
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| (...) Yes, a shame that there isn't an archive of old messages on BrickLink. So here is a copy of a message I wrote after finding a solution to the problem with the yellow cylinder. (so it's not lost in cyberspace!) (URL) my original post I decided (...) (21 years ago, 4-Apr-04, to lugnet.technic)
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