+======+======================================================+========+
|No. of| | |
|items.|Description of item. | Cost.|
|------+------------------------------------------------------+--------|
|Three |500-h.p. water-tube Sterling boilers | $15,186|
|Two |Feed pumps, George F. Blake Manufacturing Company | 740|
|One |Henry R. Worthington surface condenser | 6,539|
|Two |Electrically-driven circulating pumps on river front | 5,961|
|Three |Low-pressure compressors, Ingersoll-Sergeant Drill | 33,780|
| |Company | |
|One |High-pressure compressor, Ingersoll-Sergeant Drill | 6,665|
| |Company | |
|Three |Hydraulic power pumps, George F. Blake Manufacturing | 3,075|
| |Company | |
|Two |General Electric Company's generators coupled to Ball | 7,626|
| |and Wood engines | |
|------+------------------------------------------------------+--------|
| |Total cost of main items of plant | $79,572|
|------+------------------------------------------------------+--------|
| SUMMARY OF COST OF ONE PLANT.
|-------------------------------------------------------------+--------+
|Total cost of main items of plant | $79,572|
| | |
|Cost of four shields (including installation, demolition, | 103,560|
|large additions and renewals, piping, pumps, etc.) | |
| | |
|Cost of piping, connections, drills, derricks, installation | 101,818|
|of offices and all miscellaneous plant | |
| | |
|Cost of installation, including preparation of site | 39,534|
|-------------------------------------------------------------+--------|
|Total prime cost of one power-house plant |$324,484|
|=============================================================+========|
The following is a short description of each item of plant in Table 2:
_Boilers._--At each shaft there were three 500-h.p., water-tube boilers,
Class F (made by Sterling and Company, Chicago, Ill.). They had
independent steel stacks, 54 in. in diameter and 100 ft. above grate
level; each had 5,000 sq. ft. of heating surface and 116 sq. ft. of
grate area. The firing was by hand, and there were shaking grates and
four doors to each furnace. Under normal conditions of work, two boilers
at each plant were able to supply all the steam required. The average
working pressure of the steam was 135 lb. per sq. in.
The steam piping system was on the loop or by-pass plan. The diameter of
the pipes varied from 14 in. in the main header to 10 in. in the body of
the loop. The diameter of the exhaust steam main increased from 8 in. at
the remote machines to 20 in., and then to 30 in., at the steam
separator, which in turn was connected with the condensers. A pipe with
an automatic relief valve from the exhaust to the atmosphere was used
when the condensers were shut down. All piping was of the standard,
flanged extra-heavy type, with bronze-seated gate-valves on the
principal lines, and globe-valves on some of the auxiliary ones. There
was an 8-in. water leg on the main header fitted with a Mason-Kelly
trap, and other smaller water traps were set at suitable intervals.
Each boiler was fitted with safety valves, and there were automatic
release valves on the high-and low-pressure cylinders of each
compressor, as well as on each air receiver.
Buckwheat coal was used, and was delivered to the bins on the Manhattan
side by teams and on the Weehawken side by railroad cars or in barges,
whence it was taken to the power-house by 2-ft. gauge cars. An average
of 20 tons of coal in each 24 hours was used by each plant.
The water was taken directly from the public service supply main. The
daily quantity used was approximately 4,000 gal. for boiler purposes and
4,400 gal. for general plant use. Wooden overhead tanks having a
capacity of 14,000 gal. at each plant served as a 12-hour emergency
supply.
_Feed Pumps._--There were two feed pumps at each plant. They had a
capacity of 700 cu. ft. per min., free discharge. The plungers were
double, of 6-in. diameter, and 10-in. stroke, the steam cylinders were
of 10-in. diameter and 10-in. stroke. An injector of the "Metropolitan
Double-Tube" type, with a capacity of 700 cu. ft. per min., was fitted
to each boiler for use in emergencies.
The feed-water heater was a "No. 9 Cochrane," guaranteed to heat 45,000
lb. of water per hour, and had a total capacity of 85.7 cu. ft. It was
heated by the exhaust steam from the non-condensing auxiliary plant.
_Condenser Plant._--There were two surface condensers at each plant.
Each had a cooling surface sufficient to condense 22,500 lb. of steam
per hour, with water at a temperature of 70° Fahr. and barometer at 30
in., maintaining a vacuum of 26 in. in the condenser. Each was fitted
with a Blake, horizontal, direct-acting, vacuum pump.
_Circulating-Water Pumps._--Two circulating-water pumps, supplying salt
water directly from the Hudson River, were placed on the wharf. They
were 8-in. centrifugal pumps, each driven by a 36-h.p., General Electric
Company's direct-current motor (220 volts and 610 rev. per min.), the
current being supplied from the contractor's power-house generators. The
pumps were run alternately 24 hours each at a time. Those on the
Manhattan side were 1,300 ft. from the power-house, and delivered their
water through a 16-in. pipe; those on the Weehawken side were 450 ft.
away, and delivered through a 14-in. pipe. There was also a direct
connection with the city mains, in case of an accident to the salt-water
pumps.
_Low-Pressure Compressors._--At each plant there were three low-pressure
compressors. These were for the supply of compressed air to the working
chambers of the subaqueous shield-driven tunnels. They were also used on
occasions to supply compressed air to the cylinders of the high-pressure
compressors, thus largely increasing the capacity of the latter when
hard pressed by an unusual call on account of heavy drilling work in the
rock tunnels. They were of a new design, of duplex Corliss type, having
cross-compound steam cylinders, designed to operate condensing, but
capable of working non-condensing; the air cylinders were simple duplex.
The steam cylinder valves were of the Corliss release type, with vacuum
dash-pots. The valves in the air cylinders were mechanically-operated
piston valves, with end inlet and discharge. The engines used steam at
135 lb. pressure. The high-and low-pressure steam cylinders were 14 in.
and 30 in. in diameter, respectively, with a stroke of 36 in. and a
maximum speed of 135 rev. per min. The two air cylinders were 23½ in.
in diameter, and had a combined capacity of 35.1 cu. ft. of free air per
revolution, and, when running at 125 rev. per min., each machine had an
actual capacity of 4,389 cu. ft. of free air per min., or 263,340 cu.
ft. per hour. The air cylinders were covered by water-jackets through
which salt water from the circulating pumps flowed. A gauge pressure of
50 lb. of air could be obtained.
Each compressor was fitted with an automatic speed and air-pressure
regulator, designed to vary the cut-off according to the volume of air
required, and was provided with an after-cooler fitted with tinned-brass
tube and eight Tobin-bronze tube-plates having 809 sq. ft. of cooling
surface; each one was capable of reducing the temperature of the air
delivered by it to within 10° Fahr. of the temperature of the cooling
water when its compressor was operated at its fullest capacity. From the
after-cooler the air passed into a vertical receiver, 4 ft. 6 in. in
diameter and 12 ft. high, there being one such receiver for each
compressor. The receivers were tested to a pressure of 100 lb. per sq.
in. The after-coolers were provided with traps to collect precipitated
moisture and oil. The coolers and receivers were fitted with safety
valves set to blow off at 1 lb. above the working pressure. The air
supply was taken from without, and above the power-house roof, but in
very cold weather it could be taken from within doors.
_High-Pressure Compressors._--There was one high-pressure compressor at
each plant. Each consisted of two duplex air cylinders fitted to a
cross-compound, Corliss-Bass, steam engine. The two steam cylinders were
14 and 26 in. in diameter, respectively, and the air cylinders were
14¼ in. in diameter and had a 36-in. stroke. The air cylinder was
water-jacketed with salt water supplied from the circulating water
pumps.
The capacity was about 1,100 cu. ft. of free air per min. when running
at 85 rev. per min. and using intake air at normal pressure, but, when
receiving air from the low-pressure compressors at a pressure of 30 lb.
per sq. in., the capacity was 3,305 cu. ft. of free air per min.;
receiving air at 50 lb. per sq. in., the capacity would have been 4,847
cu. ft. of free air per min. This latter arrangement, however, called
for more air than the low-pressure compressors could deliver. With the
low-pressure compressor running at 125 rev. per min. (its maximum
speed), it could furnish enough air at 43.8 lb. per sq. in. to supply
the high-pressure compressor running at 85 rev. per min. (its maximum
speed); and, with the high-pressure compressor delivering compressed air
at 150 lb., the combined capacity of the arrangement would have been
4,389 cu. ft. of free air per min.
The air passed through a receiver, 4 ft. 6 in. in diameter and 12 ft.
high, tested under a water pressure of 225 lb. per sq. in., before being
sent through the distributing pipes.
_Hydraulic Power Pumps._--At each power-house there were three hydraulic
power pumps to operate the tunneling shields. One pump was used for each
tunnel, leaving the third as a stand-by. The duplex steam cylinders were
15 in. in diameter, with a 10-in. stroke; the duplex water rams were
2-1/8 in. in diameter with a 10-in. stroke. The pumps were designed to
work up to 6,000 lb. per sq. in., but the usual working pressure was
about 4,500 lb. The piping, which was extra heavy hydraulic, was
connected by heavy cast-steel screw couplings having a hexagonal
cross-section in the middle to enable tightening to be done with a bolt
wrench. The piping was designed to withstand a pressure of 5,500 lb. per
sq. in.
_Electric Generators._--At each plant there were two electric generators
supplying direct current for both lighting and power, at 240 volts,
through a two-wire system of mains. They were of Type M-P, Class 6, 100
kw., 400 amperes, 250 rev. per min., 240 volts no load and 250 volts
full load. They were connected direct to 10 by 20 by 14-in.,
center-crank, tandem-compound, engines of 150 h.p. at 250 rev. per min.
A switch-board, with all the necessary fuses, switches, and meters, was
provided at each plant.
_Lubrication._--In the lubricating system three distinct systems were
used, each requiring its own special grade of oil.
The journals and bearings were lubricated with ordinary engine oil by a
gravity system; the oil after use passed through a "White Star" filter,
and was pumped into a tank about 15 ft. above the engine-room floor.
The low-pressure air cylinders were lubricated with "High Test" oil,
having a flash point of 600° Fahr. The oil was forced from a receiving
tank into an elevated tank by high-pressure air. When the tank was full
the high-pressure air was turned off and the low-pressure air was turned
on, in this way the air pressure in the oil tank equalled that in the
air cylinder being lubricated, thus allowing a perfect gravity system to
exist.
The steam cylinders and the high-pressure air cylinders were fed with
oil from hand-fed automatic lubricators made by the Detroit Lubrication
Company, Detroit, Mich.
"Steam Cylinder" oil was used for the steam cylinders and "High Test"
oil (the same as used for the low-pressure air cylinders) for the
high-pressure air cylinders. The air cylinder and steam cylinder
lubricators were of the same kind, except that no condensers were
necessary. The steam cylinder and engine oil was caught on drip pans,
and, after being filtered, was used again as engine oil in the bearings.
The oil from the air cylinders was not saved, nor was that from the
steam cylinders caught at the separator.
_Cost of Operating the Power-House Plants._--In order to give an idea of
the general cost of running these plants, Tables 3 and 4 are given as
typical of the force employed and the general supplies needed for a
24-hour run of one plant. Table 3 gives a typical run during the period
of driving the shields, and Table 4 is typical of the period of concrete
construction. In the latter case the tunnels were under normal air
pressure. Before the junction of the shields, both plants were running
continuously; after the junction, but while the tunnels were still under
compressed air, only one power-house plant was operated.
TABLE 3.--COST OF OPERATING ONE POWER-HOUSE FOR 24 HOURS DURING
EXCAVATION AND METAL LINING.
===+===================+====================+=============
No.| Labor. | Rate per day. | Amount.
---+-------------------+--------------------+-------------
6 |Engineers | $3.00 | $18.00
6 |Firemen | 2.50 | 15.00
2 |Oilers | 2.00 | 4.00
2 |Laborers | 2.00 | 4.00
4 |Pumpmen | 2.75 | 11.00
2 |Electricians | 3.50 | 7.00
1 |Helper | 3.00 | 3.00
---+-------------------+--------------------+-------------
Total per day | $62.00
--------------------------------------------+-------------
Total for 30 days | $1,860.00
--------------------------------------------+-------------
Supplies.
-----------------------+--------------------+-------------
Coal (14 tons per day) | $3.25 | $45.50
Water | 7.00 | 7.00
Oil (4 gal. per day) | 0.50 | 2.00
Waste (4 lb. per day) | 0.07 | 0.28
Other supplies | 1.00 | 1.00
-----------------------+--------------------+-------------
Total per day | $55.78
--------------------------------------------+-------------
Total for 30 days | $1,673.00
--------------------------------------------+-------------
Total cost of labor and supplies for 30 days| $3,533.00
============================================+=============
_Stone-Crusher Plant._--A short description of the stone-crusher plant
will be given, as it played an important part in the economy of the
concrete work. In order to provide crushed stone for the concrete, the
contractor bought (from the contractor who built the Bergen Hill
Tunnels) the pile of trap rock excavated from these tunnels, which had
been dumped on the piece of waste ground to the north of Baldwin Avenue,
Weehawken, N. J.
The general layout of the plant is shown on Plate XXX. It consisted of a
No. 6 and a No. 8 Austin crusher, driven by an Amex, single-cylinder,
horizontal, steam engine of 120 h.p., and was capable of crushing about
225 cu. yd. of stone per 10-hour day. The crushers and conveyors were
driven from a countershaft, in turn driven from the engine by an 18-in.
belt.
TABLE 4.--COST OF OPERATING THE ONE PLANT FOR 24 HOURS DURING CONCRETE
LINING.
===+===================+====================+=============
No.| Labor. | Rate per day. | Amount.
---+-------------------+--------------------+-------------
2 |Engineers | $3.00 | $6.00
2 |Firemen | 2.50 | 5.00
2 |Pumpmen | 3.00 | 6.00
1 |Foreman Electrician| 6.00 | 6.00
1 |Electrician | 3.00 | 3.00
1 |Laborer | 2.00 | 2.00
---+-------------------+--------------------+-------------
Total per day | $28.00
--------------------------------------------+-------------
Total for 30 days | $840.00
--------------------------------------------+-------------
Supplies.
-----------------------+--------------------+-------------
Coal (14 tons per day) | $3.15 | $44.10
Oil (4 gal. per day) | 0.50 | 2.00
Water | 13.00 | 13.00
Other supplies | 2.00 | 2.00
-----------------------+--------------------+-------------
Total per day | $61.10
--------------------------------------------+-------------
Total for 30 days | $1,833.00
--------------------------------------------+-------------
Total cost of labor and supplies for 30 days| $2,673.00
============================================+=============
The process of crushing was as follows: The stone from the pile was
loaded by hand into scale-boxes which were lifted by two derricks into
the chute above the No. 6 crusher. One derrick had a 34-ft. mast and a
56-ft. boom, and was worked by a Lidgerwood steam hoister; the other had
a 23-ft. mast and a 45-ft. boom, and was worked by a "General Electric"
hoist. All the stone passed first through the No. 6 crusher, after which
it was lifted by a bucket conveyor to a screen, placed about 60 ft.
higher than and above the stone bin. The screen was a steel chute
pierced by 2½-in. circular holes, and was on a slope of about 45°; in
order to prevent the screen from choking, it was necessary to have two
men continually scraping the stone over it with hoes. All the stone
passing the screen was discharged into a bin below with a capacity of
about 220 cu. yd. The stone not passing the screen passed down a
diagonal chute to a No. 8 crusher, from which, after crushing, it was
carried back by a second bucket conveyor to the bin, into which it was
dumped without passing a screen. The No. 8 crusher was arranged so that
it could, when necessary, receive stone direct from the stone pile. The
cars in which the stone was removed could be run under the bin and
filled by opening a sliding door in the bottom of the bin. A track was
laid from the bin to connect with the contractor's surface railway in
the Weehawken Shaft yard, and on this track the stone could be
transported either to the Weehawken Shaft direct, for use on that side
of the river, or to the wharf, where it could be dumped into scows for
transportation to New York.
The cars used were 3-cu. yd. side-dump, with flap-doors, and were hauled
by two steam Dinky locomotives.
The average force employed was:
1 foreman @ $3.00 per day. Supervising.
24 laborers " 1.75 " " Loading scale-boxes for derricks.
4 laborers " 1.75 " " Feeding crushers.
2 laborers " 1.75 " " Watching screens to prevent clogging.
1 engineer " 4.00 " " Driving steam engine.
2 engineers " 3.50 " " On the derricks.
1 night watchman. Watching the plant at night.
Owing to the constant break-down of machinery, chutes, etc., inseparable
from stone-crushing work, there was always at work a repair gang
consisting of either three carpenters or three machinists, according to
the nature of the break-down.
The approximate cost of the plant was:
Machinery $5,850
Lumber 3,305
Erection labor 3,999
------
Total $13,154
The cost of the crushed stone at Weehawken amounted to about $0.91 per
cu. yd., and was made up as follows:
Cost of stone $0.22
Labor in operation of plant 0.31
Plant supplies 0.11
[B]Plant depreciation 0.27
-----
Total $0.91
[B] Assuming that the scrap value of derricks and engines is one-half
the cost, crushers one-third the cost, and other items nothing.
The crushed stone at the Manhattan Shaft cost about $1.04 per cu. yd.,
the difference of $0.13 from the Weehawken cost being made up of the
cost of transfer across the river, $0.08, and transport from the dock to
the shaft, $0.05.
_Miscellaneous Plant._--The various pieces of plant used directly in the
construction work, such as derricks, hauling engines, pumps, concrete
mixers, and forms, will be found described or at least mentioned in
connection with the methods used in construction.
The tunneling shields, however, will be described now, as much of the
explanation of the shield-driven work will not be clear unless preceded
by a good idea of their design.
Tunneling Shields.
During the period in which the original contract drawings were being
made, namely, in the latter part of 1903 and the early part of 1904,
considerable attention was given to working out detailed studies for a
type of shield which would be suitable for dealing with the various
kinds of ground through which the shield-driven tunnels had to pass.
This was done in order that, when the contract was let, the engineer's
ideas of the requirements of the shields should be thoroughly
crystallized, and so that the contractor might take advantage of this
long-thought-out design, instead of being under the necessity of placing
a hurried order for a piece of plant on which so much of the safety as
well as of the speed of his work depended. Eventually, the contractor
took over these designs as they stood, with certain minor modifications,
and the shields as built and worked gave entire satisfaction. The chief
points held in view were ample strength, easy access to the working face
combined with ease and quickness of closing the diaphragm, and general
simplicity. A clear idea of the main features of the design can be
gathered from Fig. 3 and Plate XXXI.
[A]The interior diameter of the skin was 2 in. greater than the
external diameter of the metal lining of the tunnel, which was 23 ft.
The skin was made up of three thicknesses of steel plate, a ¾-in.
plate outside and inside, with a 5/8-in. plate between; thus the
external diameter of the skin was 23 ft. 6¼ in. The length over all
(exclusive of the hood, to be described later) was 15 ft. 11-7/16 in.
The maximum overlap of the skin over the erected metal lining was 6 ft.
4½ in., and the minimum overlap, 2 ft.
There were no inside or outside cover-plates, the joints of the various
pieces of skin plates being butt-joints covered by the overlap of
adjoining plates. All riveting was flush, both inside and outside. The
whole circumference of each skin plate was made up of eight pieces, each
of which extended the entire length of the shield, the only
circumferential joint on the outside being at the junction of the
removable cutting edge (or of the hood when the latter was in position)
with the shield proper.
Forward of the back ends of the jacks, the shield was stiffened by an
annular girder supporting the skin, and in the space between the
stiffeners of which were set the 24 propelling rams used to shove the
shield ahead by pressure exerted on the last erected ring of metal
lining, as shown on Plate XXXI.
To assist in taking the thrust of these rams, gusset-plates were placed
against the end of each ram cylinder, and were carried forward to form
level brackets supporting the cast-steel cutting-edge segments. The
stiffening gussets, between which were placed the rams, were also
carried forward as level brackets, for the same purpose. The cast-steel
segmental cutting edge was attached to the front of the last mentioned
plates.
The interior structural framing consisted of two floors and three
vertical partitions, giving nine openings or pockets for access to the
face; these pockets were 2 ft. 7 in. wide, the height varying from 2 ft.
2 in. to 3 ft. 4 in., according to their location. The openings were
provided with pivoted segmental doors, which were adopted because they
could be shut without having to displace any ground which might be
flowing into the tunnel, and while open their own weight tended to close
them, being held from doing so by a simple catch.
[Illustration: PROPOSED SHIELD FOR SUBAQUEOUS TUNNELING GENERAL
ELEVATION FIG. 3.]
For passing through the varied assortment of ground before entering on
the true sub-river silt, it was decided to adopt the forward detachable
extension, or hood, which has so often proved its worth in ground
needing timber for its support, as shown in Fig. 2, Plate XXIX. This
hood extended 2 ft. 1 in. beyond the cutting edge, and from the top down
to the level of the upper platform. Additional pieces were provided by
which the hood might have been brought down as far as the lower
platform, but they were not used. Special trapezoidal steel castings
formed the junction between the hood and the cutting edge. The hood was
in nine sections, built up of two ¾-in. and one 5/8-in. skin plates,
as in the main body of the skin, and was supported by bracket plates
attached to the forward ends of the ram chambers. The hoods were bolted
in place, and were removed and replaced by regular cutting-edge steel
castings after the shields had passed the river lines.
The floors of the two platforms, of which there were eight, formed by
the division of the platforms by the upright framing, could be extended
forward 2 ft. 9 in. in front of the cutting edge, or 8 in. in front of
the hood. This motion was given by hydraulic jacks. The sliding platform
could hold a load of 7,900 lb. per sq. ft., which was equal to the
maximum head of ground and water combined. The uses of these platforms
will be described under the heading "Construction." The weight of the
structural portion of each shield was about 135 tons.
The remainder of the shield was the hydraulic part, which provided its
motive force and gave the power to the segment erector. The hydraulic
fittings weighed about 58 tons per shield, so that the total weight of
each shield was about 193 tons. The hydraulic apparatus was designed for
a maximum pressure of 5,000 lb. per sq. in., a minimum pressure of 2,000
lb., and a test pressure of 6,000 lb. The actual average pressure used
was about 3,500 lb. per sq. in.
There were 24 shoving rams, with a diameter of 8½ in. and stroke of
38 in. The main ram was single-acting. The packings could be tightened
up from the outside without removing the ram, a thing which is of the
greatest convenience, and cannot be done with the differential plunger
type. Some of the chief figures relating to the shield rams, with a
water pressure of 5,000 lb. per sq. in., are:
Forward force of one ram 275,000 lb.
Forward force of 24 rams (all) 6,600,000 "
Forward force of 24 rams 3,300 tons of 2,000 lb.
Equivalent pressure per square inch of face 105 lb.
Equivalent pressure per square foot of face 15,200 "
Pull-back force of one ram 26,400 "
Pull-back pressure on full area of ram 480 " per sq. in.
The rams developed a tendency to bend, under the severe test of shoving
the shield all closed, or nearly so, through the river silt, and it is
probable that it would have been better to make the pistons 10 in. in
diameter instead of 8½ in.
Each sliding platform was actuated by two single-acting rams, 3½ in.
in diameter and having a stroke of 2 ft. 9 in. The rams were attached to
the rear face of the shield diaphragm inside the box floors, and the
cylinders were movable, sliding freely on bearings in the floor. The
front ends of the cylinders were fixed to the front ends of the sliding
platforms. The cylinder thus supported the front end of the sliding
platform, and was designed to carry its half of the load on the
platform. Some of the leading figures in connection with the platform
rams, at a working pressure of 5,000 lb. per sq. in., are:
Forward force of each pair of rams (in each platform) 96,000 lb.
Total area of nose of sliding platform 1,060 sq. in.
Maximum reaction per square inch on nose 90 lb.
Maximum reaction per square foot on nose 13,040 "
Each shield was fitted with a single erector mounted on the rear of the
diaphragm. The erector consisted of a box-shaped frame mounted on a
central shaft revolving on bearings attached to the shield. Inside of
this frame there was a differential hydraulic plunger, 4 in. and 3 in.
in diameter and of 48-in. stroke. To the plunger head were attached two
channels sliding inside the box frame, and to the projecting ends of
these the grip was attached. At the opposite end of the box frame a
counterweight was attached which balanced about 700 lb. of the tunnel
segment at 11 ft. radius.
The erector was revolved by two single-acting rams fixed horizontally to
the back of the shield above the erector pivot through double chains and
chain wheels keyed to the erector shaft.
The principal figures connected with the erector, assuming a water
pressure of 5,000 lb. per sq. in., are:
Weight of heaviest tunnel segment 2,584 lb.
Weight of erector plunger and grip 616 "
Total weight to be handled by the erector ram 3,200 "
Total force in erector ram moving from center of shield 35,000 "
Total force in erector ram moving toward center of shield 27,500 "
Weight at 11-ft. radius which is balanced by counterweight 700 "
Maximum net weight at 11-ft. radius to be handled by
turning rams 1,884 "
Total force of each rotating ram, at 5,000 lb. per sq. in. 80,000 "
Load at 11-ft. radius, equivalent to above 3,780 "
When the shield was designed, a grip was also designed by which the
erector could handle segments without any special lugs being cast on
them. A bolt was passed through two opposite bolt holes in the
circumferential flanges of a plate. The grip jaws closed over this bolt
and locked themselves. The projecting fixed ends of the grip were for
taking the direct thrust on the grip caused by the erector ram when
placing a segment.
It happened, however, that there was delay in delivering these grips,
and, when the shield was ready to start, and the grip was not
forthcoming, Mr. Patrick Fitzgerald, the Contractor's Superintendent,
overcame this trouble by having another grip made.
In this design, also, a self-catching bolt is placed through the segment
and the grip catches the bolt. In simplicity and effectiveness in
working, this new design eventually proved a decided advance on the
original one, and, as a result, all the shields were fitted with the new
grip, and the original design was discarded.
The great drawback to the original grip was that the plate swung on the
lifting bolt, and thus brought a great strain on the bolt when held
rigidly at right angles to the erector arm. The original design was able
to handle both _A_ and _B_ segments, and key segments, without
alteration; in the new design, an auxiliary head had to be swung into
position to handle the key, but this objection did not amount to a
practical drawback.
The operating floor from which the shield was controlled, and at which
the valves were situated, was placed above the rams which rotate the
erector, and formed a protection for them. The control of the shield
rams was divided into four groups: the seven lower rams constituted one
group, the upper five, another, and the six remaining on each side, the
other two. Each group was controlled by its own stop and release valve.
Individual rams were controlled by stop-cocks.
The control of the sliding platform rams was divided into two groups, of
which all the rams on the upper floor made one, and all those in the
lower floor, the other; here, again, each group had its own stop and
release valve, and individual platforms were controlled by stop-cocks
arranged in blocks from which the pipes were carried to the rams.
The in-and-out movements of the erector ram were controlled by a
two-spindle, balanced, stop and release valve, controlled by a
hand-wheel. The erector rotating rams were controlled by a similar
valve, with four spindles, also operated by a single hand-wheel. Both
wheels were placed inside the top shield pockets, and within easy reach
of the operating platform.
The hydraulic pressure was brought through the tunnel by a 2-in.
hydraulic pipe. Connection with the shield was made by a flexible copper
pipe, the 2-in. line being extended as the shield advanced.