The great pressures used in hydraulic machines are supplied from intensifiers on the principle of that shown with the forging press in a previous chapter, or from accumulators. Water in an accumulator cylinder is subjected to a pressure of at least several hundred pounds per square inch by means of weights loaded upon the cylinder as shown in Fig. 232. The description and operation of the accumulator here shown are given as follows, viz.: A heavy base B rests on a concrete foundation and supports the accumulator. This base carries a vertical steel rod R, called the ram, and short vertical supports S on which the cylinder rests when not in operation. A bronze sleeve D, about 1/2 or 3/4 of an inch thick, is shrunk over the lower end of the ram. The ram has a hole along its axis as shown, communicating at H with the inside of the heavy cast-steel cylinder C. The upper end of the ram, which acts as a guide for the cylinder in its variable up and down travel, is steadied by the roof trusses of the building in which the equipment is installed.

Fig. 232. - Hydraulic Accumulator.

Water is forced by hydraulic pumps (steam-driven pumps with very small water plungers) through the pipe G and the opening H into the space W between the rod and the cylinder. The unbalanced pressure on the end of the bronze sleeve D is increased by the pumps until it is sufficient to raise the cylinder and the weights which it carries. These annular cast-iron weights determine the degree of pressure in the cylinder. If less pressure is desired, one or more of the weights is lifted and suspended above the accumulator.

This pressure is used by transmitting it to the controlling valves of a hydraulic press through a pipe connected at K.

Fig. 233. - Flange-Heating Furnace.

Suitable automatic controls are rigged on the accumulator to stop the pumps when the cylinder has raised its full height, and to prevent a sudden drop of the cylinder in case a pipe should suddenly break.