For which applications is an IP 68 casing recommended?
An IP 68 seal is not just appropriate for actuators working in subsea. A IP 68 casing is recommended for all operating areas which are either permanently, frequently or occasionally flooded. An IP 68 hermetic seal is also recommended for areas such as canals or water tanks where high levels of vapors are to be reckoned with. The same applies for areas where condensation buildup in the casing is likely due to large temperature fluctuations. The same applies for actuators operating in very corrosive environments (e.g. chemical gases).
Avoid matufacturers who put a time limit on the IP 68 protection e.g. IP 68 (1 h) or similar, or state a shallow depth (e.g. 1 m) in their documentation or marketing material.
If the manufacturer guarantees a hermetic seal against in inundation of water or other fluids only for a certain time or for a particular depth, you should regard such statements as nonsense. It is not possible for users to foresee times or depths to an exact degree. The manufacturer either works with fictional criterias plucked out of thin air or with empirical figures from experimental conditions with no relation to use in “live” industrial situations.
Is an IP 68 seal somewhat excessive for installations over drains canals, water tanks and other conditions in which high vapor levels are possible or certain?
No, because it is exactly these outdoor applications in which puzzling instances of corrosion can occur. The casing might well be in tact but the inside of the actuator becomes fully corroded. Determining the reason for the corrosion, correspondence with the actuator supplier, changing the actuator and the constant insecurity about further corrosion damage occurring, actually incur much higher costs than simply paying extra at the beginning for the IP 68 casing.
Is an IP 68 seal somewhat excessive for areas in which condensation buildup from large temperature fluctuations is certain? Would a heating system offered by other manufacturers not suffice?
TA Roloff also offers heating elements. These elements will often be sufficient in order to prevent water buildup in an actuator. If other factors come into play such as the need to mount an actuator upside down, it would be very difficult to guarantee long lasting and reliable operability. Heat rises, water pools at the base of the casing and it becomes very difficult to remove the water with a heating system alone.
IP 68 and explosion protection. How do they marry up and for what applications are they suitable?
Explosion protection and the protection type IP 68 have various objectives during operation. A hermetic seal ensures that no other substance can enter. Explosion protection ensures that sparks from the electromotor or other internal parts will not cause an explosion of gases in the surrounding area. TA Roloff can combine both protection types. If flammable gases can bubble up from the fluids which occasionally flood the actuator it is advisable to combine both measures.
What should I make of claims that electric actuators are not technically feasible for underwater use?
These claims have no factual basis but persist among those whose business it is to sell hydraulic actuator technology.