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 06:07:58 GMT
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Viewed:
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1350 times
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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.
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Message has 1 Reply:
 | | 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 (...) (20 years ago, 4-Apr-04, to lugnet.technic)
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Message is in Reply To:
| | Pneumatic Cylinders
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| 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 (...) (20 years ago, 3-Apr-04, to lugnet.technic)
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