While there were compressors on board located in the engine room, these were for the refrigeration engines used to chill the refrigerated cargo.
I know of no other compressors on the ship or for what purpose compressed air would be used for on the Titanic, however Britannic and Olympic were both fitted with Hydraulic Watertight Doors, which were operated with compressed air but this was not until circa 1915 - 16.
My memory is like a sieve right now, I can't remember which book I saw that in. I've been up far too long, lol. I'll comb through my books, I know I'll brush across it again, and when I do I'll be happy to post it.
In any event, would you want your ship's watertight integrity to depend on the operability of the system that provided the watertight doors with motive power? I doubt it. If Britannic's design actually required compressed air to operate the doors, she was a ship looking for a way to sink.
I don't even like the idea of the electric clutches not being fail-safe in design. It would have made more sense for the doors to close if the power was lost.
"...I don't even like the idea of the electric clutches not being fail-safe in design. It would have made more sense for the doors to close if the power was lost..."
Yes, that would have been my preference, too. Of course, beneath the deck plates next to each door there was a float attached to a rod that would release the clutch if water entered the compartment regardless of whether or not the solenoid did it's job, so in effect the clutches were provided with an automatic fail-safe - just not as immediately activated as would a "power-off/clutch released" arrangement. (A hand lever was also fitted to this rod to allow the release to be tripped by hand)
Even with some of the drawbacks we perceive in H&W's gravity-type watertight doors, when compared against the majority of power-operated door systems of the day, they had some distinct advantages. For one, with the contemporary hydraulic doors of that period, the only way to close them in the event of system failure was by hand, either locally at the door or by cranks from the deck above as was the case with the manually operated horizontal sliding doors on Titanic's higher decks. However, these hydraulically operated doors could take considerably more effort to close by hand than a conventional manually operated door, because in addition to moving the considerable weight of the door itself, one was also forcing fluid out the hydraulic cylinder, the piston of which was still firmly attached to the door.
Thanks very much for your detailed and informative posting. It is always interesting to find out where these misconceptions come from.
Actually, thinking about it, I remember about the miscaptioning of that Britannic construction photo. In a recent listing from the UFTM, I seem to remember that it had been corrected by someone at the museum. Thanks to Morgan's and your efforts. Yet I had not quite realised that this might have contributed to the confusion.
I also thought that if Olympic's doors had been changed later in her career, that it would have been shown on the numerous plans that exist in her surveys. Nor did I remember Engineering speaking of Britannic's doors as having a radically different arrangement, although it did mention the watertight door indicator.
I feared that it some misidentification like that!
Something occurred to me after reading Scott's excellent description of Titanic's doors. The jambs of the H&W design fitted fitted to the ship had to be less robust because gravity was used to make the final closure. Friction would have been a serious consideration, so the wedging action was necessarily limited--particularly the size of the wedges that did the work.
On a door closed by hydraulics, the jamb and wedges could be of any necessary size and certainly larger than on a gravity door.
This difference would not have been significant on smaller ships with less height of bulkheads. The potential water pressure against watertight doors in smaller ships would have been less simply because the compartments were not as tall. Height gives "head" to a water column, increasing pressure. That's why we put up water towers in city water distribution systems.
So, the doors fitted to Titanic had the excellent feature of not needing outside power to close. However, the size of the Olympic class ships may have gone past the adequacy of gravity driven doors.
Smaller jambs would allow the possibility that distortion of the hull and bulkheads during the sinking could allow a door to "blow open" in some manner. More robust jambs would be less likely to suffer such a fate.
I must quickly add that we have no testimonial evidence of any of Titanic's automatic watertight doors not closing properly or of "blowing open."
Even so, the possibility also exits with a gravity door that distortion of the bulkhead to which it is attached may prevent proper closure. A bent jamb could stop the door short with a gap for water to flow through. An hydraulic door could be jammed shut with physical force, provided the distortion wast not overly great.
Those are all very good observations regarding the size of the door features, to possibility of warping of the bulkhead causing failure of the door to make a watertight seal, etc.
Regarding the latter, given the breadth of the Olympic-class liners and that fact that the vertical doors on the tank top were all well inside the hull nearer the centerline, I would guess that there was very little chance of the more common ship-ship collision doing any damage severe enough to cause a problem for one of these doors. However, one has to wonder what effect severe damage to the bottom structure could have potentially had -- say, a hard grounding or other event serious enough to push upwards and deform not only the exterior shell, but the tank floors, tank top and possibly the base of the bulkhead beneath of one of these doors. In such as case the frame may become racked. Assuming the hydraulics were still operable, a hydraulic door might still be able to close completely under such circumstances, affording some protection even if it wasn't entirely watertight, where the gravity door could conceivably stop short some distance from closing fully.