Pneumatic cranes question

[DarkShadow73]

Hi - I recently built the 8460 Pneumatic Crane and it sort of uses the same setup with the back to back pneumatic cylinders as the 8421 does. If I leave the crane in the up position overnight, the cylinders somehow lose their ability to hold up the boom of both cranes. I am rather sure this has been talked about here. Is there a fix to allow the crane booms to remain upright instead of slowing losing air? I have all the tubing tight on all the valves, T-pieces, and the cylinders.

Thanks for any advice.

[Lakop]

I think the air slowly leaks out overnight.

H

[DarkShadow73]

I think the air slowly leaks out overnight.

H

Yeah I realize that, that prompted me to ask, but am wondering about a fix if possible. I've had a couple of 8421's for years, and the main model crane does the same thing. Even on the 8455 Backhoe Loader the same thing happens, the main boom's cylinder also does the same thing, it seems too heavy to hold it upright for more than a day or two at most on the model, but where are the air leaks coming from? I guess that's the biggest question. If all the tubing is tight and I've tried on all 3 models to keep the valve at the neutral position or having the switch on the valve body in the raising position.

[Lakop]

Not sure. Could be the valve or where the tubing joins a T connector. I've experienced it myself many years ago. if you're displaying the model you could always work out another way to keep the boom up.

H

[dr_spock]

You have an air leak somewhere. You could dunk the model in water and see if any air bubbles come out. Or swap parts until the boom stops dropping overnight.

One reason to use LAs for display cranes.

[Milan]

Dont put model under the water, you will get rust on the cylinders

Pneumatic cylinders will always drop when left under weight, not much you can do, except to periodically pump air.

[Graydingo]

If you've removed the hoses a few times, the ends can split. Cut off split ends with scissors and when you reattach the hoses push all the way to the base of any nipple. They will leak as it is a toy, but I feel your leak is a bit more than usual.

[DarkShadow73]

Yeah, guess there isn't much I can do. I know all the tubing is very tight on all T's, valves and cylinders. Display was my intent. I guess I could see if there is a way to add some long liftarms to keep the boom upright, maybe 13 or 15L ones, this would probably work fine with the 8421 which is studless construction, but not sure how I can accomplish this on the 8460 since it is mostly studded. Even though I prefer the studless construction because it is more sleek and realistic, I really took quite a liking to the 8460 once it was done.

I have an 8448 Supercar and 8462 Tow Truck to build, both we're produced at a time where studless construction was just being added in small amounts. I also have an 8446 Crane Truck and even though it is an odd looking beast, something kind of perked my interest. I also have an 8428 Concept Car, 8443 Log Loader, 8853 Front Loader (really like this one as well). I have an 8837(think that's the right set#) wheeled Excavator. That one I don't really like too well. I got from an adult collector and all pieces we're in fine shape, but the finished product looks rather dorky, but at least I only paid $50 for it on Bricklink a couple years ago.

If you've removed the hoses a few times, the ends can split. Cut off split ends with scissors and when you reattach the hoses push all the way to the base of any nipple. They will leak as it is a toy, but I feel your leak is a bit more than usual.

Actually the set was brand new and mint. Tubes are thus brand new and in excellent condition, its only been together for a little over a week. On the note of excess wear on tubing, I bought a used pneumatic 8455 Backhoe Loader that was 'well used' (ended up returning it to the seller as it was in much rougher shape than she described), and I had plenty of isses with split tubing.

Dont put model under the water, you will get rust on the cylinders

Pneumatic cylinders will always drop when left under weight, not much you can do, except to periodically pump air.

Glad you told me that. Problem with Lego models is they gather dust that almost always needs a wash in soapy water unless it has PF elements which most do nowadays. I didn't know about the cylinders rusting, I'll definitely not wash them, thanks for the tip. I have an 8464 Pneumatic Front Loader bought in 2001 and after a while the cylinder rams have developed some corrosion and pitting and it was never washed. I lightly wet sanded the cylinders with 1500 grit paper, but now the cylinders don't work well at all, even though I was extremely careful and made sure none of the dust from the sanding didn't enter the cylinder itself. Now I'm thinking I should have gone with 2000 grit or steel wool.

[Saberwing40k]

Actually, I'm not sure it's even possible to make a crane that is pneumatic that will not leak air over time. As a matter of fact, real hydraulic cranes and other equipment can not really keep their boom raised for long periods of time with the hydraulic system shut off. I've seen several vehicles, like Bobcat loaders, and even some large wheel loaders at an exhibition that had a locking bar, essentially a length of metal C channel that went over the extended rod of the cylinder, keeping it extended. I'd recommend that you do the same thing, as even if you glued the pneumatic hoses to the t pieces, valves, and cylinders, the valves and the cylinders would still leak a little bit of air.

As a matter of fact, this has been talked about before, and you were even the one who posted it.

http://www.eurobrick...ak#entry1433621

The solutions that Efferman and Blakbird posted should work for you.

Edited February 27, 2015 by Saberwing40k

[JayDee96]

The air is probably not leaking out of the connections at all, but around the o-ring inside the cylinder. Other than lots of grease there's probably not too much you can do, especially with air being such an unforgivable medium to contain under pressure.

Edited February 27, 2015 by JayDee96