Hello lemgineers!
I’m working on designing a claw that can be operated underwater. The plan is to use a linear actuator in a waterproof housing. The main issue is allowing the shaft to slide through without causing a leak. What’s the best way to go about this?
Would depend on how deep underwater and the pressure and so forth, but maybe look at how steam engine piston rods are sealed - an o-ring or a wiper seal would probably do the job
Look at the gland end of any hydraulic cylinder.
If you have an air line to the surface, then running the enclosure at positive pressure to negate the force of water pressure at depth might be a starting point.
I would also reconsider whether a linear actuator is the right approach. A hydraulic piston external to the housing where your motor resides reduces the complexity of any waterproofing, and might be a better approach if you’re dealing with significant depths/pressures.
If the travel distance of the rod is fairly limited, you can use a corrugated boot.
Otherwise, maybe a gland seal with positive air pressure on the dry side?
Consider a hydraulic actuator that already works underwater?
If you need a shaft to slide through the wall of your housing, Google “shaft seal” or “oil seal.” The seal usually presses into a hole in your housing, so you will want the housing to be metal rather than plastic.
https://www.mcmaster.com/products/shaft-seals/
A dynamic seal like this is going to be difficult to implement. The shaft will need to be very smooth and carefully aligned to the housing. Some small amount of water is likely to get past the seal.
I’m with @Longpork3@lemmy.nz. Consider other ways to actuate your claw that don’t require moving a part through the housing wall. I’m addition to pneumatic or hydraulic actuators outaide your housing, here’s an idea using magnets and screws:
https://org.osu.edu/osu-uwrt/2022/04/11/underwater-claw-development/
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 😍 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.