"Pneumatic Conveyor – A pneumatic conveyor system is provided to transport Marconigram forms between the Enquiry office, located on C Deck, and the Marconi Room. The suction in the conveyor tubes is created by an air pump rated at 1/2 B.H.P."
If you're really interested, I would suggest a trip to the library to read up on the theory and practical application of pneumatic conveyance. The three tubes seen in the photographs of Olympic's and Titanic's Marconi Rooms are actually two, but the camera doesn't reveal the bend in the tubing behind the operator's desk that makes one look like two. Because Titanic didn't use diverters, each tube is uni-directional. From left to right (as one views the photographs), the tubes function as: intake (to the Enquiry Office); exhaust (from the Enquiry Office); and (continuing on) the line from the air pump.