"It won't be likely to with pressure pumps going behind it and suction pumps pulling from in front. We can always put extra power on if necessary. Thus far the road has worked perfectly."
"How much power do you need to send it through, under normal conditions?"
"Our trains have been averaging about fifty tons, and for that weight we have found that a pound pressure is quite sufficient. Now, taking the tunnel's length as four thousand miles (of course it is not that long, but round figures are most convenient) and the tube width eleven and one quarter feet each and working this out we have 3,020,000 cubic feet of free air per minute or 2,904,000 cubic feet of compressed air, which would use about 70,000 horse power on the air compressor."
"But isn't the speed rather dizzy?"
"Not any more dizzy, Bob, than those old fashioned money-carrying machines that the department stores used to use—that is in comparison to size. The average speed is about 360 feet a second. Of course, the train is allowed to slow down toward the end of its run, even before it hits the braking machinery beyond the gate."
"But how much pressure did you say would be put on the back of the diaphragm—I remember that each car has a flat disc on the back that fits fairly tightly to the tube ..."
"The pressure on the back is less than seven tons. However, the disc does not fit tight. There are several leaks. For instance, the cars are as you know, run on the principle of the monorail with a guiding rail on each side. The grooves for the rails with their three rollers are in each car. There is a slight leakage of air here."
"You used the turbo type of blower, didn't you?"
"Had to because of the noise. We put some silencing devices on that and yet we could not kill all of the racket. However a new invention has come up that we will make use of soon now."