this post was submitted on 27 May 2024
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I'm late to the party, but I'm not sure why nobody mentioned the keyword "stuffing box". That's what this exact part is called in maritime operations, and as the name suggests it was traditionally a box packed with something to slow down the movement of water. You still have to bail on the other end, though, because it's not perfect.
However, since it's just a linear actuator it'd be simpler to go with an accordion-type covering. At shallow depths you could use a normal plastic one, if it needs to go deep metal ones exist. That's much simpler to deal with than an actual sliding bearing.
Sorry I'm just now seeing this, and late to the party is just fine ๐ I'm looking at redesigning it this year anyways!
I'm not sure if this is similar to what you meant by an accordion covering, but what we did was design a mold that we 3D printed and poured silicone into to create a seal/cover that will stretch as the piston of the linear actuator slides in and out.
I meant with the pleats, similar to what you see on an actual accordion, or in a bendy straw. It's how they did the joints on the Apollo space suits, for a vaguely similar application. The shape is sometimes called "bellows", but that's pretty confusing when it also refers to an air blowing technology that may or may not involve a diaphragm of any kind.
If you got enough range of movement with just a straight elastomer cylinder, that works, but if the pressure is pretty modest a variety of stretchy ducts made for HVAC or other home purposes are sold. I have some for draining rainwater, but they seem to break in stiff wind, so YMMV. You could also mold your own again.
We actually did start out with an accordion/bellows design, but found that the flexibility of the material alone was more than sufficient to handle the required distance of travel on the actuator piston!