One of the harsher, if not the harshest, environments actuators have to deal with is none other than the deep depths of the ocean. The constant heavy pressure and being submerged underwater for its entire lifespan are what make the environment so treacherous for actuators. You would think having powered actuators undersea would make for a bad idea but that is not the case.
In fact these actuators are used every day within those conditions as part of underwater machinery. Now in order to do this the actuators must have a way of dealing with all that pressure. They do this through a process of pressure equalization. By sealing oil inside the unit the actuator is able to reach the same pressure as the water around it. This oil filled design makes it possible for the internal and external pressures to be equalized continuously.
Underwater actuators like these are perfect for a variety of jobs such as controlling rudders, diving planes and underwater camera equipment. They are also used quite a bit in operating robotic arms that go underwater to perform tasks like welding or collecting research samples. To work underwater these actuators must also be able to function at very low temperatures. They can be operated effectively at temperatures as low as -30 degrees Celsius.
Because these actuators are underwater, durability is another very important factor. Land actuators are usually found in easy to reach and serviceable locations in case they need to be adjusted or repaired on the fly. Underwater actuators do not have this luxury and they can and will be used in places that are extremely difficult to get to and repair.
What this means is that the construction of these units must include parts and features that do not require much upkeep. Materials like metal, plastic and rubber are some of the most common materials used for underwater automation. However stainless steel is the best option for constructing an underwater actuator because it gives the move durability and helps control corrosion better than other materials.
One final consideration in underwater automation is making it blend into the environment. As you can imagine almost no, if any, natural objects exist undersea that function the way linear actuators do. What this means is that using an actuator underwater will more than likely disturb the environment, which is a major concern. To combat this there are actuator types that can mimic the appearance of marine wildlife with carefully constructed features, thus camouflaging itself from unwanted intrusions. This by no means is a common feature and is only used when absolutely necessary.