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 19:36:29 GMT
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Viewed:
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1879 times
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> In lugnet.technic, Mark Bellis wrote:
>
> 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.
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 blocked. That was the
problem with my pumps from the 8455. The pressure simply escaped by going back
into one of the pumps.
>
> 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.
Yes, but I must say that the grease alone, can also be the reason for
springback.
> 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?
I'll have to check that, but right now my 8455-cylinders are tied up in a model.
>
> 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.
Sounds just as boring as fixing the newer train wheels by removing excess
plastic from the frame with a knife.
> 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
I agree, it is a good recommendation to test parts like the pneumatic cylinders
before putting them to use. It can be difficult to switch them afterwards.
Martin
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Message is in Reply To:
 | | 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. (...) (21 years ago, 4-Apr-04, to lugnet.technic)
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