The New York Subway: Chapter 10, Subway Drainage
The employment of water-proofing to the exterior surfaces of the masonry shell of the tunnel, which is applied to the masonry, almost without a break along the entire subway construction, has made it unnecessary to provide an extensive system of drains, or sump pits, of any magnitude, for the collection and removal of water from the interior of the tunnel.
On the other hand, however, at each depression or point where water could collect from any cause, such as by leakage through a cable manhole covet or by the breaking of an adjacent water pipe, or the like, a sump pit or drain has been provided for carrying the water away from the interior of the tunnel.
For all locations, where such drains, or sump pits, are located above the line of the adjacent sewer, the carrying of the water away has been easy to accomplish by employing a drain pipe in connection with suitable traps and valves.
In other cases, however, where it is necessary to elevate the water, the problem has been of a different character. In such cases, where possible, at each depression where water is liable to collect, a well, or sump pit, has been constructed just outside the shell of the tunnel. The bottom of the well has been placed lower than the floor of the tunnel, so that the water can flow into the well through a drain connecting to the tunnel.
Each well is then provided with a pumping outfit; but in the case of these wells and in other locations where it is necessary to maintain pumping devices, it has not been possible to employ a uniform design of pumping equipment, as the various locations offer different conditions, each employing apparatus best suited to the requirements.
In no case, except two, is an electric pump employed, as the employment of compressed air was considered more reliable.
The several depressions at which it is necessary to maintain a pumping plant are enumerated as follows:
- No. 1-Sump at the lowest point on City Hall Loop.
- No. 2-Sump at intersection of Elm and White Streets.
- No. 3-Sump at 38th Street in the Murray Hill Tunnel.
- No. 4-Sump at intersection of 46th Street and Broadway.
- No. 5-Sump at intersection of 116th Street and Lenox Avenue.
- No. 6-Sump at intersection of 142d Street and Lenox Avenue.
- No. 7-Sump at intersection of 147th Street and Lenox Avenue.
- No. 8-Sump at about 144th Street in Harlem River approach.
- No. 9-Sump at the center of the Harlem River Tunnel.
- No. 10-Sump at intersection of Gerard Avenue and 149th Street.
In addition to the above mentioned sumps, where pumping plants are maintained, it is necessary to maintain pumping plants at the following points:
- Location No. 1-At the cable tunnel constructed under the Subway at 23d Street and Fourth Avenue.
- Location No. 2-At the sub-subway at 42d Street and Broadway.
- Location No. 3-At the portal of the Lenox Avenue extension at 148th Street.
- Location No. 4-At the southerly end of the Harlem River tube.
- Location No. 5-At the northerly end of the Harlem River tube.
- Location No. 6-At the portal at Bergen Avenue and 149th Street.
In the case of the No. 1 sump a direct-connected electric triple-plunger pump is employed, situated in a pump room about 40 feet distant from the sump pit. In the case of Nos. 2, 4, and 7 sumps, automatic air lifts are employed. This apparatus is placed in those sump wells which are not easily accessible, and the air lift was selected for the reason that no moving parts are conveyed in the air-lift construction other than the movable ball float and valve which control the device. The air lift consists of concentric piping extending several feet into the ground below the bottom of the well, and the water is elevated by the air producing a rising column of water of less specific weight than the descending column of water which is in the pipe extending below the bottom of the sump well.
In the case of Nos. 3 and 5 sumps, and for Location No. 1, automatic air-operated ejectors have been employed, for the reason that the conditions did not warrant the employment of air lifts or electric or air-operated pumps.
In the case of Nos. 6, 8, 9, and 10 sumps and for Locations Nos. 2, 4, and 5, air-operated reciprocating pumps will be employed. These pumps will be placed in readily accessible locations, where air lifts could not be used, and this type of pump was selected as being the most reliable device to employ.
In the case of Location No. 3, where provision has to be made to prevent a large amount of yard drainage, during a storm, from entering the tunnel where it descends from the portal, it was considered best to employ large submerged centrifugal pumps, operated by reciprocating air engines. Also for the portal, at Location No. 6, similar centrifugal pumps will be employed, but as compressed air is not available at this point, these pumps will be operated by electric motors.
The air supply to the air-operating pumping devices will be independent from the compressed air line which supplies air to the switch and signal system, but break-down connections will be made between the two systems, so that either system can help the other out in case of emergency.
A special air-compressor plant is located at the 148th Street repair shop, and another plant within the subway at 41st Street, for supplying air to the pumps, within the immediate locality of each compressor plant. For the more remote pumps, air will be supplied by smaller air compressors located within passenger stations. In one case, for the No. 2 sump, air will be taken from the switch and signal air-compressor plant located at the No. 11 sub-station.