Thread: calling all engineers ... waterproof pneumatic cylinder?

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I need a little help from those of you who have been building props for a while. (those with skills)

I want to build a sit up rig that I can put in a tub of water (blood). I could place the valve and the flow controls outside of the tub and run lines to the cylinder in the tub, but there lies the question? Silicone, and heat shrink tubing around the connections should keep water out at those points. So ....

Does anyone know where I can get a waterproof pneumatic cylinder?

This is what I am trying to recreate.

BLOOD BATH Animated Halloween Prop

txatty
You are going to have to go with a stainless steel double acting cylinder.
FrightProps - Halloween Decorations, Halloween Props, Pneumatic Props, Animated Props, Halloween Accessories
If you use a single acting cylinder, it will fill with water when the solenoid is deactivated.
The double acting will have pressure on both sides of the cylinder.
You will also have to use a 4 way solenoid.
FrightProps - Halloween Decorations, Halloween Props, Pneumatic Props, Animated Props, Halloween Accessories
Hope that helps.

Originally Posted by markgoodson

Well I am no expert, but I would think that anything that can hold hundreds of pounds of air pressure on the inside without leaking would also keep water out?

That's true. Air leaks are much more difficult to seal than water leaks. As far as using a double-acting cylinder goes, you may be able to attach a fitting and plastic tube to the air vent on a single-acting cylinder. Route the tube out of the water bath. Stainless steel is still a good idea to prevent rusting the cylinder, though.

txatty
The link I sent to you for cylinders is actually the ones that Frightprops recommends for underwater use.
They are probably air tight.

Cheaper brass cylinders, and really cheap crimped-together throw-aways can be used also.
The only place any rust would even be a problem is the rod, and unless you store the prop with the rod extended, in the water, that really isn't much to be worried about. If you want to, you could add an airline oiler before the prop. This will keep the rod coated with a very thin layer of oil.

Personally, I think any cylinder will be just fine, rust-wise. It's only a very short term exposure, just dry it all before you store it. I've seen cylinders at work that have operated under very hot water for several years. As was mentioned, just vent to avoid sucking water back into the cylinder. Don't worry about water leaking in around the rod, that's not going to happen.

Just another comment.......... most cylinders have a polished or chrome plated shaft that itself is pretty resistant to rust and corrosion, the oiler wouldn't hurt at all.