It is well known that the principle which is applied to the
construction of vacuum or filter pumps, and which aims at the
production of rarefied air in a certain inclosed space, may also be
applied to the production of air _pressure_.
A simple apparatus by which this may be accomplished has recently been
constructed by A. Beutell.
A tall cylindrical flask, K (see cut), is provided with an outlet tube
near the bottom, and its stopper carries two tubes, one (M) for the
entrance of a jet of water, and the other (L) for the exit of the
compressed air, which may be conducted to a blast lamp or wherever air
under pressure may be needed. The column of water entering through M
causes air to be sucked in through the little hole at c, and this air,
after arriving in the flask, is gradually compressed by the
continuously entering water.
In order that the apparatus may work properly, it is necessary to
construct the tube, M, in a particular manner, and of certain definite
proportions. Fig. 3 exhibits its bore and shape in an enlarged view. A
short distance below the orifice of the tube it is slightly expanded,
and then gradually contracts to the place, b. It then again expands to
an oblong cavity, and contracts again to a neck, e, which is a trifle
wider than that at b, and which must be so situated that the column of
water passing through b is exactly perpendicular to the center of the
aperture at e. The tube then expands again to its original diameter,
and is slightly curved, which is done to prevent any of the compressed
air in the cylinder, K, from regurgitating upward.
[Illustration: FIG. 1., FIG. 2., FIG. 3.
BEUTELL'S WATER BLAST PUMP.]
The outlet tube at A is preferably constructed as shown in Fig. 2.
Instead of being made of one piece, it is there represented as
consisting of two pieces joined together by rubber tubing, a sort of
check valve, G, being introduced into the rubber joint. By regulating
the check valve, that is by approaching it more or less to the exit of
the tube, A, the outflow of water may be regulated. It is important to
adjust this so that the cylindrical flask will always be at least half
full, and never over three-fourths filled. While the column of water
falls through the aperture at b, into the expanded portion of M, it
aspirates air through the little orifice, c, communicating with the
outer air, and this air is carried along with it into the flask, where
it accumulates until it is under a pressure equal to that of the
column of water entering the apparatus, when the latter will cease to
flow. By allowing the air to escape through L, more will be
successively compressed, so that a steady blast may be obtained.
The proportions between the diameters of the expanded and contracted
portions of the glass tube, M, are important. If the bore at b amounts
to 2.5 millimeters, that at e should be 3 millimeters. Under these
circumstances, and with a pressure of water equal to a column of 61.7
cubic centimeters, the apparatus will furnish 890 liters of air for
every 1,000 liters of water consumed. If the two diameters were: b, 1
millimeter, and e, 2.4 mm., one liter of water aspirates 2.35 liters
of air. These proportions are, no doubt, capable of
improvement.--_Chem. Zeit. and Ch. Centralbl._
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