The plant installed by the John Shields Construction Company, and taken
over by Mr. Bradley, was composed very largely of second-hand material,
and eventually most of it had to be replaced. Insufficient and
inefficient plant and delay in installation were largely responsible for
the small progress made by the Shields Company, and Mr. Bradley's
endeavor to utilize this plant not only caused much delay during the
first 8 or 10 months after he started work, but also involved large
expense.
_Power Plant._--At Weehawken the plant installed by the Shields Company
consisted of three old locomotive boilers, each having a nominal
capacity of about 125 h.p., and one Rand and one Ingersoll-Sergeant
compressor, each of a rated capacity of about 1,250 cu. ft. of free air
per min. compressed to 100 lb.
To this Mr. Bradley added two more second-hand locomotive boilers, and
another Rand compressor of the same type and capacity as the first. The
theoretical steam capacity of each of the five old locomotive boilers
was about 4,250 lb. per hour, or a total capacity of 21,250 lb. per
hour.
[Illustration: Fig. 9.
PROGRESS PROFILE--NORTH TUNNEL]
Theoretically, the demand on this steam was:
Pounds per hour.
Three compressors, about 5,600 lb. per hour each 16,800
One dynamo About 1,000
One 500-gal. pump " 1,000
One hoisting engine for elevators " 2,000
______
Total 20,800
Actually, there was considerable deficiency of steam when an endeavor
was made to work the three compressors at their full capacity.
A separate boiler was afterward installed to run the hoisting engine
for the elevators and the pumps, thus leaving a requirement of only
approximately 18,000 lb. of steam per hour, but even this was beyond the
capacity of the boilers, especially as one was almost always out of
commission.
The two Rand compressors were 24 by 24 by 30-in., straight-line,
one-stage, steam-driven, with a nominal capacity of 1,250 cu. ft. of
free air per min. at 80 rev. per min. The Ingersoll-Sergeant was of
similar type and capacity. Therefore, the theoretical quantity available
was 3,750 cu. ft. of free air per min.
The theoretical air requirements (as taken from manufacturers'
catalogues) were:
Cubic feet of free
air per minute.
20 Rand slugger drills (12 by 174) 2,088
2 Little Giant shovels
(taking air two-thirds of the time) 1,100
-----
Total 3,188
This estimate, based on the assumption (given in the catalogues) that
the drills would be working about three-fifths of the time, and the
shovels about two-thirds of the time, left apparently an ample margin
between the full capacity of the compressors and the requirements for
the drills; as a matter of fact, however, it was seldom that more than
80 lb. of air was available, and the pressure often dropped to 60 or 50
lb. at the compressors. During the time this plant was in use the
greatest distance to the drills was about 1,500 ft.
As this plant proved to be entirely inadequate to the demands, an
arrangement was made with the O'Rourke Construction Company on August
17th, 1906, whereby they agreed to supplement the air supply by 1,000
cu. ft. of free air per min. at 100 lb. pressure. This arrangement was
not altogether satisfactory, and finally (on December 5th, 1906) an
arrangement was made with the same company to supply air up to 4,000 cu.
ft. of free air per min. at 100 lb., and the old plant was shut down.
The new plant had been in use previously in the construction of the
River Tunnels. The air from it was compressed to 40 lb. by low-pressure
machines, one being used all the time and two when necessary. These
machines were built by the Ingersoll-Sergeant Company, the engines being
of the Corliss duplex type, cross-compound steam, with simple duplex air
cylinders, each compressor having a capacity of nearly 4,000 cu. ft.
of free air per min. This air, at 40 lb., was delivered to an
Ingersoll-Sergeant high-pressure machine, having Corliss cross-compound
engines, 14 by 26 by 36-in., with air cylinders of the piston inlet
type, 13¼ by 36-in., which compressed it to 100 lb. The capacity of this
latter machine, taking air at normal pressure, is 920 cu. ft. of free
air per min. working at 85 rev. per min.; by taking the air at 40 lb.,
and working at a somewhat higher speed, this machine alone supplied all
the air used at the Weehawken end (approximately 4,000 ft.) from
December, 1906, to November, 1907, and, with very few exceptions, the
pressure was steadily maintained at from 90 to 100 lb., there being no
break-down of any kind.
At Hackensack the plant taken over by Mr. Bradley consisted of six old
locomotive boilers and four Rand compressors, all of the same type as
those at Weehawken. To this he added two second-hand marine boilers,
each of a stated capacity of about 350 h.p., and two more Rand
compressors of the same type and capacity as the others, making the
total theoretical steam power available approximately 1,450 h.p., with a
compressor capacity of approximately 7,500 cu. ft. of free air per min.,
equal to about 1,500 h.p., allowing for 15% of loss.
Nowhere near the theoretical steam power was ever developed from the
boilers. The tubes of the old locomotive boilers were filled with mud in
many cases, and were always leaking. The marine boilers were not
properly installed to give the best results, and it was seldom possible
to work more than four compressors at once, or to keep the air pressure
at the power-house much greater than from 70 to 80 lb. at any time.
This plant had been built by the Shields Company on the meadows
alongside the Erie and New York, Susquehanna and Western Railroads, and
the foundations were not made sufficiently strong to resist the effect
of the vibration caused by the passing trains. It was impossible to keep
the steam connections tight, and there was not only the loss of steam
due to leaky joints, but positive danger of one of the main steam lines
breaking entirely. After attempting to operate this plant for nearly 5
months, Mr. Bradley determined to abandon the site and the boilers, and
build a new plant, farther back from the railroad, on solid ground, in
such a position that a spur track could be built to a coal trestle in
front of the boilers.
Two pairs of Stirling boilers, with a total capacity of 2,000 h.p., were
installed. As a rule, at times of maximum demand, three of the boilers
were in use; after the Central Shaft was stopped, two were generally
sufficient, until, toward the latter part of the excavation, the losses
in the transmission of the air made it necessary to keep three going.
Eight compressors (the six old ones with two brought from Weehawken),
were installed in the new power-house. All were of the same type,
namely, Rand, straight-line, steam-driven, 24 by 24 by 30-in., each with
a nominal capacity of 1,250 cu. ft. of free air per min. Seven of these
were generally worked to their full capacity in order to keep up the
necessary supply of air.
The maximum requirements of air at this end were primarily estimated as
follows:
Central Shaft, four headings 24 drills.
Hackensack, two working faces 20 drills.
----------
Total 44 drills.
Cubic feet of free
air per minute.
44 Slugger drills (25 by 174) require 4,350
2 Steam shovels 1,600
Pumps and machine-shop, say 1,000
4 Hoisting engines, placing concrete 2,000
4 Derricks 2,000
------
Total 10,950
The theoretical capacity of the whole eight compressors was:
1250 × 8 = 10,000 cu. ft. of free air per min.
It was considered that not more than two-thirds of the above equipment
would be working at the same time; the actual requirement, therefore,
was taken at about 8,000 cu. ft. of free air per min., thus leaving a
margin of one spare compressor.
As actually worked out, there were probably never more than eight drills
working at any one time at the Central Shaft, and this work was entirely
suspended in June, 1907, before there was any demand for power in
connection with the tunnel lining. The heaviest actual requirement,
therefore, was approximately as follows:
(_A_) _Previous to June 25th, 1907:_
Cubic feet of free
air per minute.
40 Drills (22 by 174) 3,828
2 Shovels 1,600
Pumps and machine-shop, say 1,000
2 Derricks 1,000
-----
Total 7,428
(_B_) _After November, 1907_ (_after completion of enlargement of
Central Shaft headings_):
Cubic feet of free
air per minute.
32 Drills (17 by 174) 2,958
2 Shovels 1,600
Pumps, etc 1,000
3 Hoisting engines on concrete,
each working one-third time 500
2 Derricks 1,000
-----
Total 7,058
The average number of drillers per shift was about 25 at the two main
working faces. There were also from 5 to 10 drills trimming and cleaning
up for concrete, say an average of 7, making 32 in all.
After November 1st, it actually required three boilers under steam all
the time, and not less than seven compressors running at full capacity,
to keep the air at proper pressure, the theoretical capacity of the
compressors being 8,750 cu. ft. of free air per min., as against 7,000
to 7,400 cu. ft., the theoretical maximum requirement.
Some of this deficiency was due to losses in transmission, part also was
due to the fact that the actual was probably considerably below the
theoretical capacity of the compressors.