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Pneumatic failures


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#1 Good old Lego builder

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Posted 05 November 2012 - 07:04 PM

Hello all!

After many years, a year or two ago I opened my old boxes of lego, most of them from the '80's and rebuild all my 'City' stuff  including a train and also added some new stuff.
Last year I did some building in Model Team scale and now last week I presented myself with the Unimog. Still building, great fun! Never did studless building.
So now you know were I come from.

In my collection I have the forklift 8843. A while back I tried to have pneumatic parts working. They didn't.....
The cylinder rod didn't move. So I helped it a bit...... And the I had the rod in my hands, no longer attached to the cylinder. I tried to put it back in, but it came loose everytime. So (with excessive force) I opened the cylinder, re-attached the rod to the rubber thing in it, lubricated it a bit, closed the cylinder again. When I now blow in it, via a small tube (yes, please envision it) it works. Me happy.

However.... When I connected everything the right way, when I use the pump, and push, I see the rod come out a bit, but also go back once the pump goes back to its starting position. Does anybody know what part is malfunctioning?

By the way, the pump has also come loose, just like the cylinder, so I guess it is a total loss, but maybe I can fix it somehow?

Greetings!

#2 Alasdair Ryan

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Posted 06 November 2012 - 12:59 AM

your forklift has one of the longer pneumatic rams which only has one inlet this means that when yo need it to be retracted it requires some assistance ether by the weight of  the arm/load or by a rubber band.

The single inlet pneumatic rams also require a valve block and a switch to work properly,have you tried pushing air through these to test that they work?

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#3 Blakbird

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Posted 06 November 2012 - 01:27 AM

View PostAlasdair Ryan, on 06 November 2012 - 12:59 AM, said:

your forklift has one of the longer pneumatic rams which only has one inlet this means that when yo need it to be retracted it requires some assistance ether by the weight of  the arm/load or by a rubber band.

It should not need any rubber bands or weight to retract if connected properly.  These old single port actuators have no check valve to they are capable of extending due to positive (blowing) pressure gradient or retracting due to negative (sucking) pressure gradient.  But only the valve block will allow the latter to occur.  If you just connect it to a regular pump directly, it won't work.  Read a bit more about it here.  The 2nd generation pneumatics (which we still use) work quite differently.  You can read about those here.

Sounds like you have the old pneumatics so you have to make sure you only hook them up with the valve block in the circuit.
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#4 Good old Lego builder

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Posted 06 November 2012 - 03:34 PM

Thanks, I'm gonna try this. The block is connected in the circuit. I don't know if it works correct. I'll try this as well as the switch.
Is there a way to test all items seperately?

#5 Jetro

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Posted 26 November 2012 - 05:59 PM

Sort of... first, you can take the cylinder or the pump, cover the outlet/inlet and try to extend or retract the ram. You should feel the resistance and and when you let go of the ram it should go back to the position it was in when you blocked the outlet.

Second you can hook up the pump to the cylinder. Make sure the ram of the cylinder is down before you connect. Press the pump and the cylinder should go up. Release the pump and if the spring is still working properly, the ram of the pump should go up and the one in th cylinder should go down.

Then connect the pump to the central inlet of the distribution block. When you pump the air should come out only one of the other outlets and when you release the pump (or pull it up) the air should only go in one of the inlets.You can do the same for the manual valve and move the switch to feel the air coming out or going in the inlet opposite to the side you switch the lever.

#6 Good old Lego builder

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Posted 26 November 2012 - 06:46 PM

OK, I, try that somerime. Right know, pump is broken (the 'ram' of the pump has come loose of the rubber thing inside, same for the cylinder)  :-(

Edited by Good old Lego builder, 26 November 2012 - 06:47 PM.




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