Apparatus for Measuring the Velocity of Air and other Gas Currents.
Year: 1897

page_text: Date of Application, 15th Dec., 1897
Complete Specification Left, 14th Sept., 1898-Accepted. 19th Nov. 1898
PROVISIONAL SPECIFICATION.
Apparatus for Measuring the Velocity of Air and other Gas Currents.
I, HERMANN KÜHNE, of 25-35, New Broad Street, London, E.C., Engineer,
do hereby declare the nature of this invention to be as follows;-
My invention is intended to measure the velocity of air and other gas currents
in the flues of furnaces, chimneys and other closed ducts as also the velocity of
wind. The instrument consists of a cylindrical glass tube in which a light and
well fitting piston or diaphragm can move.
...;
The glass tube is provided at one or both ends with suitable holders or caps.
The piston is suspended by means of an elastic medium preferably a fine cylin-
drically wound spiral spring from one of the caps.
By means of suitable pipe connections the duct in which the current to be
measured is contained is connected with one of the caps or holders of the glass
tube while an aperture or apertures at the other end of the glass tube admit
the pressure of the atmosphere or other gas or air pressure. A difference in
pressure is thus set up on the two sides of the piston tending to draw the latter in
the direction of the smaller pressure, against the force of the spring until the
tension or resistance of the latter balances the difference in pressure. From the
position of the piston within the glass tube the velocity of the current may be
read.
The piston is preferably made of very light material and must have such a
shape that it closes the glass tube as tightly as possible and moves up and down
in the glass tube parallel with itself and with least possible friction. The piston
may be guided by the walls of the glass tube or centrally on a wire or rod.
scale may be provided either on the glass tube or on the piston itself to measure
the deflection of the piston.
A
As the draft to be measured in different ducts varies considerably it is necessary
to be able to adjust the spring to different tensions. In one modification of my
apparatus this is effected by arranging a screw in one of the holders having fingers
or other suitable means whereby the effective length of the spring can be reduced
or increased. Another adjustment may besides be provided whereby after adjust-
ing the strength of the spring the piston may be set to zero of the scale or vice
-versa.
In order to measure the force of the wind the latter is collected in a suitable
arrangement of tubes and is made to exert a pressure on the piston through one
end of the tube while the other end is protected from the wind.
It is clearly understood that one or more springs may be used. Cotton or
asbestos or other suitable filters may be applied between the instrument and the
current to exclude dust.
1
1007
:
MARKS & CLERK,
18, Southampton Buildings, London, W.C., and
13, Temple Street, Birmingham, Agents.

page_text: Apparatus for Measuring the Velocity of Air and other Gas Currents.
I, HERMANN KÜHNE, Engineer, of 25-35, New Broad Street, in the City of
London, do hereby declare the nature of this invention and in what manner the
same is to be performed, to be particularly described and ascertained in and by
the following statement:-
My invention is intended to measure the velocity of air and other gas currents
in the flues of furnaces, chimneys and like ducts or passages. The instrument
consists of a cylindrical tube of glass or like transparent material in which a light
well fitting bucket shaped piston is fitted and moves. The glass tube is pro-
vided at one or both ends with suitable holders or caps. The piston is sus-
pended by means of an elastic medium preferably a fine cylindrically wound
spiral spring to one of the caps.
By means of suitable pipe connections the duct in which the current to be
measured is contained is connected with one of the caps or holders of the glass
tube, while the other end of the glass tube admits the pressure of the atmosphere.
A difference of pressure is thus set up on the two sides of the piston tending to draw
the latter in the direction of the smaller pressure against the force of the spring
until the tension or resistance of the latter balances the difference in pressure.
From the position of the piston within the glass tube the velocity of the current
can be read.
The piston is constructed of very light material in order that the extension
of the spring should be as far as possible caused only by the current and not by
the weight of the piston. The piston is therefore preferably made of very thin
aluminium or blown glass, and its shape is so arranged as to ensure a sufficiently
good fit in the glass tube and a parallel motion therein while providing sufficient
freedom from friction. These conditions are best fulfilled by giving the piston
the shape of a deep cylindrical bucket. The cylindrical part of the bucket is
preferably provided with ring shaped grooves which form an air packing.
Sufficient lightness of the piston, lightness combined with great mobility and
parallel guidance are thereby attained. As an elastic medium for the suspension
of the piston a light cylindrically wound spring of thin steel wire is preferably
used, the spring having a slightly smaller diameter than the inside of the piston
or its grooves.
The salient and leading features of the invention to be hereinafter more par-
ticularly described consists in direct or positive reading of the gas current by
the motion of a piston against a spring within a tube of transparent material
such as glass, and by the terra positive or direct reading is meant the measure-
ment and indication of the said currents without the interposition of clockwork
and dials as in ordinary gauges.
The means adopted to carry my invention into effect are illustrated in the
accompanying sheets of drawings as follows:-
Figure 1 is an elevation partly in section of the measuring apparatus shown
in place on an ordinary boiler flue to indicate the draught.
Figure 1 is the piston removed from the tube and in section.
Figure 2 is a vertical longitudinal section of a modification of the spring retain-
ing and adjusting device.
Figure 3 is a vertical longitudinal section of a further modification of the spring
retaining and adjusting device.
Figures 4 and 5 are respectively side elevation and plan of a portion of the
mechanism shown in Figure 2.
Figure 6 is a plan of the apparatus shown in Figure 2.

page_text: Figure 7 is an elevation partly in section of the apparatus modified to measure
forced draught.
Figure 8 illustrates the application of the apparatus to measuring differences
between two currents of air in a boiler furnace.
Figures 1 and 1^ illustrate the salient features of the invention. The trans-
parent tube A preferably made of glass is cemented with its lower end into the
metal cap H, and this cap is attached to the brickwork K and tube L by a screwed
flange and bolts or in any other convenient manner. The tube L is bent and
reaches with its end into the duct or flue M containing the current to be
measured and projects in the same direction as the flow of the said current indi-
cated by the arrows. The upper end of the glass tube carries a cap or cover C
having one or more apertures D. The piston E is suspended by the spring F
in such a manner that the latter holds the piston in its centre, while the spring
may be fixed either to the centre of the cover C or at a point of its own periphery.
A distinct mark may be put on the piston, or the upper or lower edge of the
piston may be used as a mark, and in this modification the lower edge cdis so
used. When using the apparatus to indicate natural draught (as in this modifica-
tion) the tube is marked with a zero as shown and graduated downwards to
represent vacuum inches of water pressure, though it is evident that any other
suitable readings may be indicated upon the tube. The gases in the flue M and
consequently the air underneath when the boiler is in operation are rarified, and
the atmospheric pressure therefore elongates the spring until the resistance of
the latter is equal to the difference in pressure above and below the piston, and
from the position which the edge cd thereof assumes the velocity of the current
and the vacuum can be read directly against the graduations on the glass. It is
advantageous to construct the spring F of such a strength that its own weight
plus that of the piston just extends the spring slightly when at the zero position,
so that the piston E is always floating on the spring and thus secure the indica-
tion of even a very slight current.
Figures 2, 4, 5, and 6 of the drawings illustrate a modification of the device.
The instrument herein before described would be sufficient for all purposes if
the velocity of the currents or draught were constant but as this is not the case
and to obviate the necessity of having different strengths of spring the following
construction is adopted so that any required alteration of the position of the
piston in the tube or the tension of the spring F can be effected. For this pur-
pose a handscrew G, is introduced through the cover C, the screw having prefer-
ably the same pitch as the spring F when the coils of the latter are close together.
The end of the screw projecting into the glass tube A carries a round dished
disc N arranged with a spiral circumference of the same pitch as one coil of the
spring F. To admit the free passage of the air above the piston E the disc has
several apertures U clearly shown in plan Figure 5 and the upturned margin of
this disc N is interrupted at the point of the termination of its spiral to allow
one coil of the spring F to pass. It is evident that a rotation of the hand screw G
will either gather in or release one coil of the spring F and thus effect the object
of this modification viz. alter the position of the piston in the tube and the spring
tension according to the amount desired.
Figure 3 is a further modification of the adjusting devices illustrated at
Figures 2, 4, 5, and 6. The disc N is replaced by fixing to the lower end of the
screw G spirally arranged arms 0 preferably three in number having at their
ends hooks T which engage or embrace one coil of the spring as clearly shown in
the drawing. Upon rotating the hand-screw G the coils of the spring are gathered
in or released whereby the strength of the spring and position of the piston is
adjusted at will to suit the special requirements of any velocity or current. It
is evident that when the zero is cut upon the glass tube and it is found necessary
to considerably alter the strength of the spring a further adjustment of the piston
in the tube becomes necessary so that the mark upon the piston or the edge cd
thereof may be made to coincide with the said zero. For this purpose the cover C

page_text: is made deep and provided with a screw V so that the piston E spring F, and
hand screw G may be raised or lowered together and to the amount required. As
an alternative adjustment the scale may be made separate and sliding upon the
glass.
'
4327 **
Figure 7 of the drawings illustrates the modification used to measure forced
draught. In this case the bottom of the glass tube is open and a suitable stop P
to prevent the piston E being blown out of the tube altogether is placed in the
position shown. The cover C is closed and has no apertures therein but is screwed
air-tight on the glass tube, and the pressure from the air duct Q is admitted to
the top of the piston by the passage W, the whole apparatus being attached in
the manner shown to the side of the duct. The other details are similarly
lettered and operate in a similar manner to the modifications hereinbefore
described.
"
Figure 8 illustrates in sectional elevation the apparatus employed to measure
the differences and variations in the pressure above and below the fire bars in a
boiler furnace where forced draught is employed. In all applications of the instru-
ment described so far it is assumed that artificial pressure is acting on one side
The
of the piston, and the natural pressure of the atmosphere on the other.
instrument, may, however, also be used to measure the difference between two
artificial pressures, and in the following manner; -
The tube A has a closed cap C as in Figure 7 and it is attached to the fire
door R to a pipe r projecting within the furnace. The bottom of the tube A is
attached to a cap H and a bend S which projects through the closed space under-
neath the fire bars s. It is evident that the pressure under the fire bars s will'
be greater than that above the fire and that a mark such as Z could be arranged
on the tube to indicate the proper difference required so that the piston would
move up when the difference increased as would occur with undue clinkering in
the bars or move down when the difference decreased as would occur with the
bars improperly covered, and thus indicate the fact to the engineer.
It is to be clearly understood that more than one spring may be used, and that
the piston may be made of any suitable substance or form, and that it may be guided
centrally on a wire or rod. Cotton or asbestos, or other suitable filters may be
applied between the instrument and the currents to exclude dust.
Having now particularly described and ascertained the nature of my said
invention, and in what manner the same is to be performed I declare that what
I claim is: -
1. In an apparatus for measuring the velocity of gases in combination; a tube
of transparent material connected at one end to the passage in which the gases are
moving and at the other end to atmosphere, a piston in the tube moving against
the resistance of a spring also contained therein, and a scale upon the tube against
which the movements of the piston can be directly read.
2. In an apparatus for measuring the velocity of gases in combination; a tube
of transparent material connected. at one end to the passage in which the gases
are moving and at the other end to atmosphere; a piston in the tube moving
against the resistance of a spring also contained therein, a perforated' cap at the
atmospheric side with a regulating screw carrying a spiral disc to wind'the several
coils of the spring into or out of action, and a scale upon the 'tube against which
the movements of the piston can be directly read.
3. In an apparatus for measuring the velocity of gases in combination"; a tube
of transparent material connected at one end to the passage in which the gases
are moving and at the other end to atmosphere, a piston in the tube moving
against the resistance of a spring also contained therein, a close cap on the pressure
side of the tube with a regulating screw carrying spirally arranged hooks to wind
the several coils of the spring into or out of action, and a scale upon the tube
against which the movements of the 'piston can be directly read!
T
1:0
4: In an apparatus for measuring the difference'in velocity of flow of gases in

page_text: two passages, in combination: -a tube of transparent material connected at one
end to one passage and at the other end to the other passage, a piston in the
tube moving against the resistance of a spring also contained therein, means for
adjusting the tension of the spring and position of the piston, and a scale upon
the tube against which the movement of the piston can be directly read.
Dated this 14th day of September 1898.