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 07:40:06 GMT
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Viewed:
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1491 times
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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
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Message has 2 Replies:
 | | Re: Pneumatic Cylinders
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| "Martin Bruun" <Citembe@dkmail.zzn.com> wrote in message news:HvMyMu.8u9@lugnet.com... (...) pneumatic (...) The amount (...) cylinders by (...) air can (...) I have succesfully done the same with 4 of the cylinders from the 8455 set. (...) be (...) (20 years ago, 4-Apr-04, to lugnet.technic)
| | | Re: Pneumatic Cylinders
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| (...) 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. (...) (20 years ago, 4-Apr-04, to lugnet.technic)
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Message is in Reply To:
| | Re: Pneumatic Cylinders
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| (...) Hi Mark, Here is a post by Martin Bruun on the subject that may interest you: (URL) 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 (...) (20 years ago, 4-Apr-04, to lugnet.technic)
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