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 cover 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.