Another great postal history article: "The Pneumatic Mail Tubes: New York's Hidden Highway And Its Development" https://about.usps.com/who/profile/history/pdf/

Another great postal history article: "The Pneumatic Mail Tubes: New York's Hidden Highway And Its Development" https://about.usps.com/who/profile/history/pdf/pneumatic-tubes.pdf https://about.usps.com/who/profile/history/pdf/pneumatic-tub... Throughput: > The operation of the Pneumatic Tube System involved air forced cylinders known as "carriers", traveling in a spinning motion, through a well-greased tube at 30 miles an hour. At its peak productivity six million pieces of mail would whisk through the system daily at a rate of 5 carriers a minute with each carriers maximum load of approximately 500 letters Shaking out the system: > The first cylindrical carrier to travel through the New York City [pneumatic tube] system was one that contained a Bible, a flag and a copy of the Constitution. The second contained an imitation peach in honor of Senator Chauncy Depew, a driving force in this project. He was fondly known as "The Peach". A third carrier had a black cat in it, for reasons unknown to this author. Diagnosing and fixing stalls in the network: > The occasional carrier stalls in a tube it could be easily detected. Each receiving machine was equipped with a "tell-tale" fan. If a carrier failed to arrive on time the air pressure would fall to level that would cause the fan to stop revolving. The operator at the affected station would call the switchboard at the telephone number PE 6-7000. On a control board there, the blocking carrier could be located through colored lights designating each station. In 99% of the cases the arrested carrier could be made mobile again by increasing the air pressure behind the blockage and decreasing air pressure in front of it. This would in effect cause a vacuum. In the 1% of the time that these methods did not work a maintenance crew would have had to go out and dig up the streets. Perks for staff operating the system: > Recently I met an old friend who told me her father was once a rocketeer [responsible for the sending and receiving of the carriers]. In conversation with him I learned that he had spent some time working on the Pneumatic Tube System at the Bronx General Post Office. [...] He told me something off the record. Since there was a renowned sandwich shop in the vicinity of the Bronx General Post Office, they often got orders from the downtown postal stations. The sandwiches were delivered through the system. Now that's what I call a real submarine sandwich!