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 lb. |
| Total weight to be handled by the erector ram | 3,200 lb. |
| Total force in erector ram moving from center of shield | 35,000 lb. |
| Total force in erector ram moving toward center of shield | 27,500 lb. |
| Weight at 11-ft. radius which is balanced by counterweight | 700 lb. |
| Maximum net weight at 11-ft. radius to be handled by turning rams | 1,884 lb. |
| Total force of each rotating ram, at 5,000 lb. per sq. in. | 80,000 lb. |
| Load at 11-ft. radius, equivalent to above | 3,780 lb. |
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 Aand Bsegments, 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.