Improvements in Governors for Air Compressors Driven by Electric Motors.
Year: 1898

page_text: Date of Application, 8th N.v., 1898-Accepted, 14th Jan., 1899
COMPLETE SPECIFICATION.
Improvements in Governors for Air Compressors Driven by Electric
Motors.
We, THE BRITISH THOMSON-HOUSTON COMPANY LIMITED, of 83, Cannon Street,
in the City of London, Electrical Engineers, do hereby declare the nature of this
invention (which has been communicated to us from abroad by Sam. H. Libby,
and William B. Potter, residing at Schenectady, in the County of Schenectady,
State of New York, United States of America, Electrical Engineers;) and in what
manner the same is to be performed to be particularly described and ascertained
in and by the following statement:-
The present invention relates to governors for air compressors, which are so
arranged that when the air pressure in the receiving tank rises above or
falls below a certain point, the air compressor is automatically started or stopped,
as the case may be. The invention relates to governors used in connection with
compressors driven by electric motors, wherein a suitable contact device is
arranged to make and break the motor circuit.
One of the objects of the present invention is to provide a governor for an air
compressor in which the air pressure of the system is directly utilized to actuate
the mechanism for disconnecting the motor power from the compressor with an
auxiliary means for regulating the action of the air pressure.
A further object of the invention is to provide a governor for an electric motor
driven air compressor, which is so arranged that the direct air pressure of the
system is utilized to actuate the circuit controlling mechanism of the motor when
it is desired to interrupt the circuit thereof, with an auxiliary means so arranged
that when the air pressure is below maximum it prevents the admission of air to
the switch actuating mechanism. but which, when the pressure rises above normal,
opens a valve admitting air to the cylinder of the switch actuating device.
The invention also relates to certain novel features more fully described and
claimed hereinafter.
In the accompanying drawings attached to and made a part of this specification.
Fig. 1 is a front elevation, partially in section, of our improved apparatus; Fig. 2
is a sectional view taken on the line 2-2 of Fig. 1; Fig. 3 is a modification of
the switch mechanism and Fig. 4 is a diagrammatic view showing the relations
of the several parts.
The cast-iron base A of the governor is mounted on a support shown in Fig. 1,
On the upper
and secured thereto by bolts entering the holes A¹ in the base.
end of the base is a coil of wire B which energizes the magnet for interrupting
the arcs formed when the circuit is interrupted between the stationary brushes C
and the movable contacts D. Secured to the base A by a bolt-E is a pole-piece F.
and to the latter is secured by screws an arc deflector G having separators G¹
situated between the contacts D. Extending outward from the base A and forming
a part of the magnetic circuit are lugs A2, A3 in which the shaft H is mounted
The contacts D are mounted on iron fingers D1, also forming a shaft of the mag.
netic circuit, and having hubs D2, D3 which are mounted on the shaft H but

page_text: separated therefrom by insulation. Mounted on a piece of wood I secured to the
base A by means of screws are the brushes C. Each brush is provided with a suit-
able spring to enable it to make good contact with the moving contacts D.
A binding post C₁is provided for each brush. The stationary brushes C, of
which there are four, are connected as follows: the two outside ones to the line
and the middle one to the magnet coil B. The contacts D are divided electrically
into pairs, one pair being mounted on the finger D³, and the other pair on the
finger D³. The relation of the contacts will be more fully described in connection
with Fig. 4.
The circuit of the magnetic lines is from the core of the magnet B, the pole
pieces F, to the iron fingers D¹, the shaft H, the lugs A2, A³ in which the shaft
is mounted, the base A, to the point of starting. Any are formed by the inter-
rupting of the circuit will be immediately destroyed by the magnet, and the
separators G¹ prevent the are from jumping from one contact D to another.
Rigidly mounted on the shaft H between the hubs D2, D3 is a forked arm J to
which is hinged the piece J¹ through which motion is imparted from the piston
to the shaft H. Pivoted to a projection of the base is an arm K having a roller
on its outer end engaging with a flattened portion of the piece J¹ and tending to
hold it in the position shown. Extending downward from the base is a projection
in which is mounted the end of the spring K', the other end being secured to the
arm K. Suitable means are provided for adjusting the tension of the spring. The
arm K is prevented from moving any farther down by a. projection A5 on the
base, which engages with the under part. On the lower part of the base is formed
a lug A' to which is detachably secured the pneumatic portion of the governor.
The governor is provided with a main body of cast metal M, and has a flange M
at the upper portion for securing it to the lug A of the base A. In the upper
end is formed the main cylinder N in which the piston N¹ is adapted to travel;
the piston is provided with a suitable packing on the lower end, and at its upper
end with a rounded socket into which the lower end of the piece J¹ projects. The
piece J is not secured to the piston, but merely rests in the bottom of the socket
formed therein. By this construction the pneumatic part of the apparatus can
be removed as a whole from the switching mechanism by simply removing the
bolts M². At the lower end is formed an auxiliary cylinder O in which is
mounted a piston O¹. Secured to the lower end of the casting M by a screw
thread in a pipe P and between the end of the pipe and the casting is a head Pi
to which one end of the spring P is secured. Extending through the head P¹
is a rod Q having on its lower end a screw threaded portion upon which the
nut Qis mounted; to this nut is secured the outer end of the spring P2. The
pipe P serves to protect the rod and nut; and by holding the nut from rotating,
the tension of the spring can readily be changed by applying a wrench to the
squared end of the rod and rotating it. On the inner end of the rod is a collar P³
and engaging therewith is the pivoted lever R. The piston 01 is provided with
a packing to insure a good fit with the cylinder, and on its lower end is pro-
vided with a socket into which the end of the rod Q projects, the latter being
retained in position by the pressure of the spring P2. On the left side a slot is
provided through which projects the lever R. On the inner end of the piston is
mounted a pin 03 having a slight enlargement in the lower part forming a seat
for the springs 04, 05 which are situated above and below it. A cap 03 is em-
ployed to furnish a support for the upper end of the spring 04 and at the same
time act as a guide for the pin. The inner end of the pin is tapered and is
adapted to engage with the hole S which forms a valve connecting the auxiliary
cylinder with the main cylinder N. At the left of the auxiliary cylinder and
parallel with it is an exhaust valve T, consisting of a screw threaded piece T¹ in
which is mounted the spring pressed plunger T². The plunger is formed with
screws in the side which connects with the passage N2 leading from the main
cylinder N, and a pin T which projects through the piece T and engages with
an adjusting screw carried by the lever R. On the right side of the casting M

page_text: is a screw threaded projection U upon which is mounted a strainer Vs to prevent
dirt from entering the governor from the pressure pipe V which is connected to
the receiving tank W₁. The piston O' can readily be removed by unscrewing the
pipe P and removing the lever R.
In Fig. 3 is shown a modification of the invention, whereby a quick make and
break of the motor circuit is obtained. The finger D¹ is made of iron and its
upper end is provided with a contact 1) which engages with the stationary
brush C. A hub is provided with a finger, which is mounted on the shaft H, and
is suitably insulated therefrom. Mounted on the shaft H is a piece H¹ upon which
are mounted the pins a, b. Between the pin a and the base A is an auxiliary
spring c which is arranged to work over a dead centre. The piston N' works
in the cylinder N and connected thereto by a pin N2 is the piece J¹. The upper
end of the piece J' is provided with a slot in which the pin 6 travels. To return
the piston and piece J¹ to place an extension spring K is secured at one end to
the casting A and at the other end to the piece J. When the piston N¹ is forced
upward, the pin b engages with the bottom of the slot in the piece J', and as soon
as the pin a has moved to a point below the centre of the shaft H, the spring c
will open the circuit between the contact D and the brush C with a snap. The
end of the piston N¹ striking the washer between the casting M and the flange A*
would limit the outward movement of the finger D'.
In Fig. 4 is shown a diagrammatic view of a system to which our invention is
applied. At W is represented an air compressor of any suitable type, which is
driven by the series motor X; this motor is preferably direct connected, and for
the purpose of illustration is shown as belted.
We have found that series motors possess certain advantages over other types
for this kind of work, for the field winding, being in series with the armature,
will prevent a sudden rush of current through the armature, at the time the cir-
cuit is closed, and at the same time the field builds up as the current increases
in the armature. We prefer to dispense with the use of auxiliary resistance in
the motor circuit, so that the motor may respond more quickly when the circuit
is closed, and by using a series motor the field will act as an inductive resistance
and prevent a too great rush of current until the speed of the motor increases to
normal, when the counter electro-motive force in the armature will regulate the
flow of current. The receiving tank W is connected by a pipe to the com-
pressor W and to the governor by the pressure pipe V, which is provided with
a suitable strainer V and an insulating coupling V
Current enters by the trolley 1 and passes through a part of the contacts on the
switch mechanism, thence through the coil B of the blow-out magnet, the remain-
ing contacts on the switch, to the field and armature of the motor X to ground.
It will be seen that the fingers D2, D3 of the switch mechanism form bridges
between the pairs of stationary brushes C and that the coil B unites the middle
pair of stationary brushes. The circuit is interrupted at four points in series,
which reduces the arc formed at each point, so that it may readily be extinguished
without damage to the contacts. If desired, an increased number of points can
be arranged at which the circuit is interrupted.
The operation of our invention will now be described: The pipe V being con-
nected to the receiving tank and the cylinder O, there is, under normal conditions,
a certain amount of air pressure in the auxiliary cylinder 0 acting on the piston (1
against the pressure of the spring P2; so long as the spring pressure preponder-
ates, the parts remain as shown, and the circuit through the switch mechanism
is closed and the motor drives the air compressor. When the air pressure in the
receiving tank rises to a point where it is greater than that of the spring, the
piston 01 moves downward causing the pin 02 to be withdrawn from the valves S,
the latter connecting the main and auxiliary cylinders. The arrangement of the
parts is such that the piston O' has a slight movement before the pin 02 opens
the valve S and a very small movement of the pin will cause a large opening of
the valve, and air is freely admitted to the cylinder N, thereby causing the

page_text: piston N¹ to respond quickly and move the piece J¹ upward and transmit motion
to the shaft H, which causes the circuit between the contacts D and the brushes C
to be interrupted. The piston will remain in its upper position as long as the
air pressure is above normal, and the motor circuit will be interrupted. As soon
as the pressure decreases the piston O' moves upward and the pin 02 closes the
valve S, then the collar P3 engages with the lever R, moving the latter upward,
causing the adjusting screw to engage with the pin 1 and open the valve which
permits the air to escape from the cylinder N, and allows the piston and contact 1)
to return to the position shown under the action of the spring K¹, thereby closing
the motor circuit.
The action of the modification shown in Fig. 3 is the same as above, except
that the finger D¹ has a snap action due to the spring a moving over a dead centre.
It will be seen that the governor is operated by direct air pressure from the
receiving tank W1, and that the pressure is controlled by the auxiliary cylinder
and piston. By this arrangement we are enabled to provide a quick acting
governor and one responsive to very slight changes in the air pressure.
Having now particularly described and ascertained the nature of our said
invention (as communicated to us from abroad) and in what manner the same is
to be performed, we declare that what we claim is:-
1. In a pneumatic governor for air compressors the combination of a switch
mechanism, a piston and cylinder for actuating the switch mechanism, an
auxiliary piston and cylinder, a valve between the cylinders, a spring supported
pin actuated by the auxiliary piston for opening and closing the valve, a spring
tending to maintain the auxiliary piston in its normal position, an exhaust valve
connecting with the switch actuating cylinder, a spring pressed device normally
closing the exhaust valve, and means controlled by the auxiliary piston for open-
ing the exhaust valve.
2. In a pneumatic governor for air compressors, the combination of a switch
mechanism mounted for oscillating movement, contacts on the switch arranged
to break the circuit at a number of points simultaneously a spring normally main-
taining the switch in a closed position, a piston and cylinder arranged to open the
switch when the air pressure becomes too great, and auxiliary means controlling
the admission of air to the cylinder.
3. In a pneumatic governor for air compressors, the combination of switch con-
tacts mounted for oscillatory movement, stationary brushes engaging therewith,
a main piston and cylinder operating by direct air pressure to move the contacts
in one direction, a spring to move the contacts in the opposite direction, an
auxiliary spring connected to a stationary part of the base and the switch, arranged
to work over a dead centre, and an auxiliary piston and cylinder for controlling
the admission of air to the main cylinder.
4. In a pneumatic governor for air compressors, the combination of a switch
for opening and closing an electric circuit, a main cylinder and piston for actua-
ting the switch, an auxiliary piston and cylinder, and a valve between the main
auxiliary cylinders actuated by the auxiliary piston and having a movement in-
dependent thereof.
5. In a pneumatic governor for air compressors. the combination of a switch for
opening and closing an electric circuit, a main piston cylinder for actuating the
switch, an auxiliary piston and cylinder, and a spring-supported valve located
between the cylinders and actuated by the auxiliary piston, and means permitting
a limited movement of the valve independent of the piston.
6. In a pneumatic governor for air compressors, the combination of a base, con-
tacts mounted on the base for oscillating movement, a cylinder bolted to the base
in which is mounted a piston for actuating the contacts, an auxiliary cylinder
formed integral with the main cylinder and connected thereto by an air passage,
and a valve for closing and opening the air passage actuated by a piston but
having a limited movement independent thereof.

page_text: 7. In a pneumatic governor for air compressors, the combination of a metal
base, a shaft mounted in bearings upon the base, contacts carried by the shaft
and adapted to engage with stationary contacts, an arm mounted on the shaft,
a piece secured to the arm, and a piston for actuating the switch having a socket
in which one end of the piece is seated.
8. In a pneumatic governor for air compressors, the combination of a switch,
a main piston and cylinder for actuating the switch, and auxiliary piston and
cylinder for regulating the admission of air to the main cylinder, and a spring-
supported valve carried by the auxiliary piston.
9. In a pneumatic governor for air compressors, the combination of a switch
a main piston and cylinder for operating the switch, an auxiliary piston and
cylinder for regulating the admission of air to the main cylinder, a valve carried
by the auxiliary piston for varying an opening between the main and auxiliary
cylinders, and springs supporting the valve in such manner that it is free to move
in two directions from a central position independent of the piston.
10. In a pneumatic governor for air compressors, the combination of a switch
mechanism mounted on a metal base, main and auxiliary cylinders formed in one
piece and bolted to the base in such manner that they can be removed without
disturbing the switch mechanism, an opening between the cylinders, a spring-
pressed valve carried by the auxiliary piston for varying the extent of said open-
ing, an adjustable extension spring tending to move the auxiliary piston to one
end of its cylinder, and a spring-pressed exhaust valve.
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3T
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1000
THE BRITISH THOMSON-HOUSTON Co., LTD.,
W. MARTINDALE,
A. R. MONKS,
Directors.
ALFRED CLEMENTS,
Assistant Secretary.