I. Low Pressure Compressors.
C. Compressors without Pistons.
1. Water-Apparatus.-Of this variety they are two types, that in which the compression is produced only by the progressive reduction of the volume occupied by the air in a reservoir in which water is admitted; and that in which the compression is produced by the entrainment of the air by means of a liquid vein escaping under a given pressure. The first may be termed: (I.) Simple Displacement Apparatus. Machines of this description are used in some of the pneumatic-dispatch stations of Paris.
An example is given in Fig. 138. The machine consists of a water-reservoir 5 feet 2 inches in diameter, 12 feet 2 inches in length, and 64.7 cubic feet in capacity, and two air-chambers, 208 cubic feet volume. One tube connects the reservoir with the city water-mains, another serves for emptying the reservoir, and a third on the upper portion of the latter communicates with the air-chambers. The air-chambers are connected as shown, and from one a tube leads directly to the pneumatic conduit. If the three receptacles be filled with air, and placed in communication with one another, but shut off from the pneumatic pipe, water enterin the reservoir at a pressure of about 35 feet drives out the air, and compresses it in the two chambers. When the reservoir is fille , air is reduced from a volume of 663 cubic feet to one of 416 cubic feet, and the pressure amounts to 1.59 absolute atmosphere. (2.) Entrainment Apparatus. To this class belongs the well-known water-bellows or trompe of the Catalan forges.
An improved device On the same principle hag been invented by
M. Romilly, and is illustrated in Fig. 139. This apparatus is
formed of a conical tube a, having a valve S, which prevents the
air escaping from the reservoir to which the tube is attached.
Water is led in the compressing reservoir through an ajutage
0, in the form of a liquid vein at a given pressure which entrains
air with it, and so effects compression of the latter in the reservoir
V. The reservoir is 282.4 cubic feet in capacity, and M. Romilly
has determined that with water at 35 feet pressure a quantity
of air can be introduced equal to .465 of the volume of the water
employed raising the air-pressure to 1.6 atmosphere.