Improvements in and relating to Pneumatically Actuated Open Circuit Controllers for Electric Motors.
Year: 1897

page_text: Date of Application, 8th June, 1897-Accepted, 17th July, 1897
Improvements in and relating to Pneumatically Actuated Open
Circuit Controllers for Electric Motors.
We, THE BRITISH THOMSON-HOUSTON COMPANY, LIMITED, of S3, 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 Edward D.
Priest, and Frank A. Merrick, both of Schenectady County of Schenectady,
State of New York, United States of America 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 pneumatically-actuated series-parallel con-
trollers for electric motors, which are adapted to connect the motors in series with
a suitable resistance for starting, gradually reduce the resistance by including
other resistances in multiple therewith, and finally short-circuit the resistance,
leaving the motors in series; then reinsert the resistance, interrupt the circuit,
change the motor connections from series to parallel, re-establish the circuit, and
cut out the resistance, in the same manner as described in connection with the
series relation.
Controllers of this class are known as open circuit" controllers, in distinction
from "bridge" controllers wherein the circuit is maintained with one or more
motors while changing from series to parallel.
Our invention has for one of its objects to do away with a large number of
the contacts commonly employed in a series-parallel controller, and at the same
time to reduce the angular movement of the operating device; to accomplish this
the contact steps of the resistance are arranged in such a manner that they have a
double utility when changing from the slowest to the highest speed connections of
the motors. A single operating handle is employed, the first time it operates to
cut out resistance from circuit with the motors, and as it returns to the "off"
position, the resistance is re-inserted; a movement beyond the "off" position
causes the handle to operate a switch for shifting the relation that the motors
bear to one another, and as the handle passes the "off" position and re-establishes
the circuit, the speed of the motors is changed, due to the shifting above referred
to, and the speed is gradually increased as resistance is cut out.
A further object of the invention is to accomplish the changes outlined above
by means of pneumatically-operated mechanism.
The invention also has for its object to provide separate and independent means
for cutting the steps of resistance out of and into circuit with the motors, and
also to provide means for automatically interrupting the circuit through any
resistance contact in case the actuating device at this particular point fails to
work, and to accomplish this without interfering with the operation of the
controller.
The invention further provides means for short-circuiting the operating
resistances after the total resistance of the circuit has been reduced to a
oredetermined amount.
The invention also has for its object to so arrange the contact-actuating devices

page_text: and switches, that in case the supply of air fails, the several parts are automatically
returned to the "off" position; thus interrupting the circuit of the motors.
The invention has for its object to arrange the coils which energize the blow-out
magnet in such a manner that any coil or coils may readily be removed without
disturbing the remainder.
The invention also relates to the construction of the chutes which are provided
these are
at each pair of resistance contacts;
so arranged that they are
independently detachable, permitting the insertion of new ones in case of accident.
The invention also has for its object to provide a valve, which is actuated step
by step by means of a device operated by the main operating handle, to supply
the air for actuating the commutating switch.
The invention also relates to details of construction more fully described and
claimed hereinafter.
In carrying out the invention, a single operating handle is employed adapted
to move to and fro, cutting resistance out of and into circuit with the motors by
means of pneumatically-actuated pistons, each piston representing one resistance
step.
In addition to the above, the handle operates an auxiliary valve which controls
the switches for establishing the series and parallel relation of the motors; the
handle and valve being so arranged that the first time the handle engages with
the valve-actuating device the motors will be connected in series and the second
time in parallel, alternating each time the handle is returned to a predetermined
point. The series and parallel switches are mounted on a suitable support and
are adapted to reciprocate from one set of contacts to another; these are actuated
by pistons, and the supply of air for operating them is controlled by the auxiliary
valve.
To extinguish the arcs formed when the series and parallel switches are thrown,
a blow-out magnet, common to both, is provided; this has two pole pieces hinged
to the core each carrying an, are deflector adapted to restrain the arc in the proper
direction. The blow-out magnet for the resistance contacts is made of a number
of separately-wound coils mounted on a common core; this core is supported at
both ends, and to replace any coil which may be injured, the core is released at
the ends and withdrawn from the coils, the latter being supported from underneath
as soon as the core is lowered. In addition to the blow-out magnet each resistance
contact is provided with a separate box or chute and these are so arranged that
they may readily be removed if injured.
Extending through the base are a number of small pipes surrounded by the
metal forming the base, having been placed in the mould before the metal was
poured in; this presents a decided advantage in the construction, for it does away
with a large number of small tubes or pipes, which, if allowed to remain in ay
exposed place, are liable to injury, and further, the liability to leakage due to
joints and imperfections is greatly reduced. Each pipe leads from a suitable
balanced valve to a cylinder whose piston actuates a resistance contact; by this
construction the operation of each contact is entirely independent of the others,
and in case the movable contact binds or welds with the stationary contacts, a
piece of soft metal which forms a part of the movable, contacts fuses, and the
resistance step which was formerly connected thereby is omitted, the balance of
the apparatus working as before, by reason of the multiple connection of the
resistance contacts.
The air for operating the pistons is obtained from a suitable reservoir, and each
piston or contact device is provided with a spring arranged in such a manner that
it will automatically return the piston or contact device to the "off" position as
soon as the supply of air fails. The resistance of the circuit is decreased by
including multiple resistance paths in circuit therewith; it is decreased in this
manner until it has reached a predetermined amount, after which a short-circuiting
switch actuated by means of a suitable piston, short-circuits the entire resistance
and the motors are in direct connection with the source of supply.

page_text: In the accompanying drawings, attached to and made part of this specification,
Fig. 1 is a side elevation of a controller illustrating our invention; Fig. 2 is a
partial plan view, Fig. 3 is a front end elevation with the pole pieces and arc
deflectors removed; Fig. 4 is an enlarged cross-section on the line 4-4 of Fig. 1;
Fig. 5 is a plan view of the base showing the resistance-controlling valve and
ports; Fig. 6 is a sectional view of the same; Fig. 7 is a detail view of the
auxiliary valve; Figs. 8, 9 and 10 are details of the same; Fig. 11 is a sectional
view taken on the line 11-11 of Fig. 3 and shows the switches for changing the
motors from series to parallel; Figs. 12 and 13 are detail views of the blow-out
magnet coils and support, Fig. 14 is a diagrammatic view of the circuit connections
and operating mechanism.
Mounted on the base A are two supports A', to which is secured the secondary
base B; this furnishes a support or bearing for the piston rods C which actuate
the contacts D carried thereby. In the present case there are thirty of these
pistons and contacts, but the number can be varied to suit the requirements. Extend-
ing lengthwise of the base is a support E made of wood, to which the contacts F
are secured; these are connected by the leads F¹ to the resistance in any desired
manner. On the ends of the support E are mounted pieces E' extending trans-
versely thereto; these pieces form the support for the rectangular frame G which
forms a support for the contacts F3, and at the same time electrically connects
them together.
Extending parallel with the wooden piece E and just above it, is an iron bar H¹
forming a core and support for the blow-out magnet coils H; this bar is supported
at the ends in a manner shown in Figs. 12 and 13. Secured to the cross piece E¹
by suitable bolts is a casting H2; this is provided with two projecting lugs forming
a support for the eye-bolt I, the latter supporting the core H. Extending trans-
versely to the core H and between the coils H, are pieces G' which form the
polar projections of the magnet. These are arranged with downwardly-extending
projections G2, shown in dotted lines in Fig. 4, and are adapted to blow the arc
upward which is formed when the circuit is interrupted between the contacts F2
and F. To remove a coil H, the nuts holding the eye-bolts I are released,
allowing the coils to rest on the wooden piece E; the core is then withdrawn and
any coil may be replaced or repaired without disturbing the remainder.
Each contact is provided with a separate chute J; these are somewhat larger at
the top than at the bottom, and are provided with extensions which prevent the
jumping of an arc from contact ) to the next adjoining in a horizontal direction.
The chutes are arranged to he readily removed in case of injury; between them
and the rectangular frame G are strips L which serve as an additional insulation.
The pieces are mounted on the support E and form binding posts for the
leads they also extend upward into the chute J and are provided with
removable contact tips F. On the opposite side of the chute is a corresponding
tip F3 mounted directly on the rectangular frame G; the latter being a conductor,
all the contact pieces are connected in multiple, and as one after the other of
the circuits is closed by means of contact D bridging the space between the
contacts F2 and F3, the resistance is decreased until it reaches a predetermined
amount, then it is short-circuited by the switch R (Figs. 3, 11 and 14). The
Contact D is composed of two pieces D'; these are united by a strip of metal D²
which is of sufficient capacity to carry the normal amount of current, but when an
excess of current occurs, as would be occasioned if the moving and stationary
contacts fused or stuck together, then the piece D2 would fuse, and so far as the
working of the balance of the apparatus is concerned it would have no effect other
than to leave out that particular resistance step. It is not intended that the
pieces I shall take the place of the regular circuit-breakers and fuses; they only
serve to protect certain portions of the apparatus.
The contact D is carried by a wooden rod D which is mounted in a socket D4
and held therein by means of the cotter pin D. This is to enable the contact D
to be readily replaced in case of injury without disturbing other portions of the

page_text: apparatus. The piston rod C, upon which the socket D* is supported, is provided
with a bearing U secured to the secondary base B and provided with a pro-
jection C2 which engages with a slot in the rod C to prevent the contact D from
twisting out of line. On the end of the piston rod is a head of any desired
construction, and extending between a collar on the rod and the cylinder C3 (the
latter being provided with a thread and screwed into the base), is a spring C
which is extended each time the contact is forced upward, due to the air being
admitted to the cylinder, and remains so until the supply of air is cut off from
tne cylinder, when it returns the piston and contact to the position shown in Fig. 4.
Figs. 4, 5 and 6 show the arrangement of the valve and its several parts. In
the centre of the base A is a thickened portion in which the pipes or tubes N
leading from the cylinders to the valve are placed. These pipes are made of any
suitable material, and are bent to the required shape and placed in the mould
prior to the pouring in of the molten metal; by this construction the pipes are
rigidly held in place, are protected against injury, and are subject to a minimum.
amount of leakage due to imperfection in the joints. Each pipe extends upward
and corresponding holes are provided in the casting A2 which is bolted to the
base A. The central portion of A2 is bored out to form a cylinder, and the opening
thus formed connects with the passages leading to the several pipes M; to adjust
the size of these openings set-screws M¹ with extensions are provided and are
adapted to vary the opening of the port as they are screwed up or down; they
also operate to cut out a port in case of injury to contacts D.
On the right-hand end of the casting A² is a screw-threaded plug M2 which,
forms a bearing for the rod M³, the latter being connected to the lever M* pivoted
to the frame and connected by a link to the lever M which is secured to the
lower end of the main actuating shaft O operated by means of the lever 01.
Located in front of the plug M2 is a hole Me forming the exhaust port for the
air which is released after the piston M moves to the left. Extending outward
to the left is a cylinder M8; this is also provided with a piston, and the two pistons
are connected together by a rod having a universal joint M. This joint com-
pensates for any irregularities in the alignment of the two cylinders. Air is
admitted under pressure from the pipe M10, and as the pistons by their
are balanced, very little effort is required to operate the valve.
arrangement
In Fig.
the cylinders C³ and their pistons have been removed to illustrate
more clearly the arrangement of the valve and ports. The holes F4 are to permit..
the leads F to pass through to the resistance.
Figs. 2, 3 and 11 illustrate in detail the series-parallel and resistance short-
circuiting switches. The series-parallel switch P is mounted on a shaft provided
with suitable bearings and is adapted to reciprocate from contacts P¹ to P². The
outer end of switch P is provided with a copper contact and between it and the
operating device is a piece of iron P3 covered by mica or similar material and
forming a part of the magnetic circuit through the pole S¹. The contact
brushes P1, P2, and P4 are mounted in vertical blocks of wood, and are provided
with suitable springs, and stops for limiting their movement. Cylinders Q, Q¹
are situated on the sides and their pistons are connected together by means of
the rod Q. Keyed to the shaft P are arms Q3; these are in engagement with the
springs Q which are so arranged that they return the switch P to the position
shown in the figures as soon as the air is cut off from either of the cylinders.
4
The resistance short-circuiting switch R is adapted to engage with one set of
brushes R¹; these are connected in circuit in such a manner that when the blade R 5
is in engagement with the brush R¹ the resistance of the circuit is short-circuited.
This short-circuiting is the last step or running position before changing from
series to parallel, and is again the last step when the motors are in parallel. As
this switch operates only on one set of contacts, a single cylinder R2 is used
provided with a piston for closing the circuit and with a spring R³ for opening 5
the circuit after the air pressure has been relieved.
To blow out the arc formed when the circuit is interrupted, an energizing coil S

page_text: is mounted on a core which is cast integral with the back of the frame. Pivoted
to the core are two pole pieces S₁; to these are secured arc reflectors S2 adapted
to be swung outward to permit inspection of the contacts.
Figs. 7, 8, 9 and 10 are detail views of the auxiliary valve. O is the main
operating shaft of the controller. Secured to his is an arm T which in certain
positions of the operating handle O is in engagement with the plunger T" which
actuates the valve T2 through the medium of a ratchet and pawl T³. The ratchet
has six teeth, and each time the plunger T is forced inward, compressing the
spring T, the ratchet advances one step.
The valve T2, is composed of a casing a, provided with three openings,-the
middle one for the inlet pipe a leading from the valve to the base A, the left
hand one a² for the series switch cylinder, and the third one a³ for the multiple
switch cylinder. The ratchet bis fixed to the end of the shaft b¹, which is pro-
vided at its inner end with a disc b2 having three holes therein; these are adapted
at intervals to coincide with the ports leading to the cylinders Q, Q. For
example, the air enters by inlet pipe a¹ and as soon as the piston M moves beyond
its opening in the casting A2, passes to the chamber surrounding the disc b2, and
is prevented from escaping by means of the screw-threaded plug ; thence it
passes upward through the hole 4 of the disc, coinciding in the present position
with the opening 6, which leads to the pipe, and the series switch cylinder Q.
When the air pressure is relieved by moving the piston M, Fig. 6, to the left
beyond the opening a', the air is permitted to escape to the atmosphere through
the opening M6, and the switch P is returned to the position shown by means
of the spring Q.
There being three openings in the disc 62, and two ports leading outward with a
six-tooth ratchet actuating the valve, the next movement of the plunger T¹ would
advance the valve disc one-sixth of a revolution; this would close the port 65 for
the hole in the disc would no longer coincide, but the hole would have
advanced until it was opposite the opening 67, which leads to the nipe a³, and the
multiple switch cylinder. The next movement, consisting of one-sixth of a
revolution, would bring the hole 68 to a position coinciding with the position of
the hole 6 shown in the drawing, and air would again be admitted to the series
switch cylinder.
Air is received from a suitable source of supply by means of the pipe M10 which
opens into a chamber formed by the cylinder M8; the piston M² being between
the source of supply and the auxiliary valve T2, it controls the air thereto and
the port opening into the cylinder A² exhausts through the opening M6. In
addition to the exhaust through the opening M as previously described, a
secondary system is provided. Extending upward through the shaft 1 (Figs. 9
and 10) is an opening 6P which is open to the atmosphere; holes 10 and 612
are located in the disc 2 and connect with the opening by suitable passages;
these holes are so arranged that as the disc is rotated they will at intervals coincide
with the ports and b permitting the air from the cylinders to escape to the
atmosphere. This secondary system prevents the pocketing of air in the
cylinders Q, Q and Q when the commutating is quickly performed, which if
allowed to escape slowly would retard the action of the switches R and P.
Referring to Fig. 2, the operation will be described; the sector C is provided
with a suitable number of notches, each notch indicating one step in the con-
troller is the first notch of the resistance steps. The handle is shown as in
the off position. As it is moved toward the front end of the controller, air is
admitted to either the series or parallel switch cylinder through the auxiliary
valve T depending upon which position it occupies. Assuming that the valve
is set for the series cylinder Q and it is desired to set it for the multiple cylinder Q',
the handle O is forced backward until it reaches the pin c²; this will cause the
arm T mounted on the same shaft as the handle O¹, to force the plunger against
the spring T and advance the ratchet b ahead one notch, which will establish a
connection between the inlet pipe and the multiple switch cylinder and air will

page_text: be admitted thereto while the operating handle moves from the "
to the notch and establishes a multiple relation of the motors.
off" position
As the handle is moved to and from the off" position, resistance is cut out
of and into circuit with the motors by reason of the contacts D making and
breaking circuit with the contacts F2 and F3. This has no effect on the relation
of the motors, for that is controlled by the auxiliary valve T2; but each time the
handle O is moved backward until it strikes the pin a new circuit relation of
the motors will be established when the handle passes the off position moving
toward the front of the controller, and thus completes the circuit.
".
The resistance of the circuit will be reduced step by step as the handle O' is
advanced, and when the handle reaches the notch c³, air will be admitted by
means of the main valve to the cylinder R2 and the switch R will be thrown to
the left and engage with the contacts R' and short circuit the resistance.
In Fig. 14 is shown a diagrammatic view of the circuit connections and the
cylinders for operating the switches. The motors are shown as connected in
pairs d and d, and in circuit with the brushes. P and the movable switch contact P.
When the piston M7 is advanced, it first admits air to the port on the right; this
is connected with the inlet pipe a¹ of the auxiliary valve T2, and if this valve is
set for the series position of the switch P, air will be admitted to the cylinder Q,
and its piston will force the switch P to the right and into engagement with the
brushes P which connect the group of motors d and d' in series., Current is
received from the trolley e, and as soon as the contacts D are forced into engage-
ment with the stationary contacts F2 and F, the circuit is established with a
certain amount of resistance; this resistance is gradually reduced by moving the
piston in the direction of the arrow, which movement admits air to the cylinders C,
and the contacts D include multiple resistance paths in circuit; these paths are
added to the circuit one by one until the resistance is very low, when the piston M
reaches the port f, and air is admitted to the cylinder R2, which forces the contact R
into engagement with the brushes R', and the resistance is short circuited. The
action is the same each time the circuit is closed; the position of the valve T’
determining whether the motors are connected in series or parallel.
Having now particularly described and ascertained the nature of our said in-
vention, (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 controller such as herein referred to, the combination of a valve, means
for operating the valve, and contacts controlled by the valve for establishing
various motor combinations, the relation of the valve and operating mechanism
being such that the first time the operating mechanism is brought to a predeter-
mined position, one relation of the motors is established, and the next time a
different relation.
2. In a controller the combination of an operating device, a valve controlled
thereby, contacts for varying the resistance of the circuit, and an independent
auxiliary valve for establishing different motor combinations, actuated by the
handle at intervals.
3. In a controller, the combination of an operating device, a valve controlled
thereby, means for varying the resistance of the circuit, an independent auxiliary
valve, means controlled thereby, for establishing different motor combinations,
and means for imparting a step by step motion to the auxiliary valve.
4. In a pneumatic controller, the combination of a valve, contacts for regulating
the resistance of the circuit, a commutating switch, an auxiliary valve controlling
the operation of the commutating switch, and an operating mechanism for the
valves bearing such a relation to the working parts that it establishes a certain
relation of the motor circuits the first time it is moved to a predetermined position,
and a different relation the next time it is moved to the same position.
5. In a pneumatic controller, the combination of a reciprocating valve
mechanism, contacts controlled thereby for regulating the resistance of the motor

page_text: circuit, a rotary valve mechanism, and contacts controlled thereby for establisning
lifferent motor combinations.
6. In a pneumatic controller, the combination of a reciprocating valve
mechanism, a plurality of separately-actuated contact devices controlled thereby,
an auxiliary valve actuated at a certain predetermined position of the operating
handle, and a switch controlled thereby for establishing a series or parallel relation
of the motor circuits.
7. In a controller provided with a single operating handle, the combination of a
plurality of pneumatically-operated contact devices adapted to vary the resistance
of the circuit when the motors are connected in series, and a switch contact con-
trolled by the handle for simultaneously closing the circuit of a number of contacts
when it is desired to establish a new relation of the motor circuits.
8. In a pneumatic controller, the combination of a plurality of separately-
actuated resistance contacts, pistons and cylinders for operating the contacts, and a
switch contact for simultaneously closing the circuit of a plurality of stationary
contacts.
9. In a controller, the combination of a main valve for regulating the admission
of air to the resistance contact cylinders, a series-parallel switch provided with a
contact for simultaneously closing the circuit of a plurality of stationary contacts,
means for operating the switch, an independent auxiliary valve for controlling the
means, and a handle for operating the main and auxiliary valves.
10. In a pneumatic controller, the combination of a resistance, a plurality of
separately actuated resistance contacts, a switch provided with a contact for short
circuiting the resistance at a predetermined point by simultaneously closing the
circuit of a plurality of stationary contacts, and a valve controlled by the actuating
handle of the controller for regulating the operation of the contacts and the
short-circuiting switch.
11. In a controller, the combination of a pneumatically actuated switch for
coupling the motors in series, separate pneumatically-actuated contacts for closing
the circuit and reducing the resistance, a valve for regulating the operation of the
contacts, a switch for short-circuiting the resistance, a switch for shifting the
motor convections from series to parallel, and pneumatically-actuated contacts for
reducing the resistance of the circuit.
12. In a controller, the combination of separate contacts pneumatically actuated
for varying the resistance of the circuit, a switch for establishing a series or
parallel relation of the motors, and a switch adapted to short circuit the resistance
each time it is reduced to a predetermined amount.
13. In a blow-out magnet, the combination of a core energized by a plurality
of separately-removable coils, and means at the ends of the core for lowering it to
remove the coils.
14. In a controller the combination of a base to which a plurality of resistance
cylinders are secured, an auxiliary base supporting the contacts and blow-out
magnet, bearings on the auxiliary base for the resistance contacts, and a valve
mounted on the base of the controller for regulating the admission of air to the
cylinders.
15. In a controller the combination of a plurality of energizing coils for a
blow-out magnet a removable core for the magnets having end supports, and a base
to which the end supports are secured, adapted to form a support for the coils when
the core is removed.
16. In a controller, the combination of a base, pipes surrounded by the metal
forming the base, and a valve for controlling the air which passess through the
pipes.
17. In a controller, the combination of a rectangular frame supported by the
base, contacts secured to the frame, other contacts secured to the base, and a
separate removable chute for each pair of contacts.
18. In a controller, the combination of an open-ended cylinder, a piston working
in the cylinder, a spring for returning the piston to place after the air pressure

page_text: has been relieved, and a contact device operated by the piston and removably
secured thereto.
19. In a controller, the combination of a plurality of stationary contacts,
separately operated contacts engaging therewith, and means for cutting ut
individual contacts without interfering with the operation of the controller.
20. In a pneumatic controller, the combination of a switch blade, pistons and
cylinders for positively actuating it situated on both sides of its centre or
" off"
position, and springs for returning it to the off" position, when the air pressure
is relieved.
21. In a pneumatic controller, the combination of a valve adapted to regulate
the supply of air to the commutating switches, an operating handle, and means
actuated by the handle for imparting a step-by-step rotary movement to the valve.
22. In a pneumatic controller, the combination of a valve, a rachet for operating
the valve, a pawl, mounted on a spring-pressed rod and engaging therewith and an
arm forming an extension of the handle adapted to operate the valve.
23. In a controller, the combination of two stationary contacts, a movable con-
tact adapted to bridge the space between the stationary contact comprising two
conducting pieces mounted on an insulating support and connected by a piece of
fuse metal, a piston to which the movable contact is secured, and a cylinder in
which the piston is mounted.
24. In a pneumatic controller, the combination of a valve, contacts controlled
by the valve for varying the motor circuit, and means for imparting a step-by-step
movement to the valve.
25. In a pneumatic controller, the combination of a valve, contacts controlled
thereby for establishing a series or parallel relation of the motors, and means for
imparting a rotary step-by-step movement to the valve.
26. In a pneumatic controller, the combination of a rotary valve, contacts con-
trolled thereby, means for imparting a rotary movement to the valve, a
reciprocating valve, contacts controlled thereby, and means for imparting a
reciprocating motion to the valve.
27. In a pneumatic controller, the combination of a plurality of separately-
actuated contacts, pistons and cylinders for operating the contacts, a fuse mounted
on each contact, and a valve for regulating the movement of the contacts.
28. In a pneumatic controller, the combination of a valve, a plurality of ports
leading from the valve, a plurality of pistons controlled thereby, and means for
closing a port or ports when it is desired to prevent a piston or pistons from
operating.
29. In a pneumatic controller, the combination of a valve, a plurality of ports
leading from the valve, a plurality of resistance contacts controlled by the valve, a
valve-actuating device, and set screws adapted to regulate the opening from the
valve to the ports.
30. In a pneumatic controller, the combination of a valve, contacts controlled
thereby, a cylinder secured in a suitable base, a piston mounted for movement
in the cylinder, contacts mounted on the piston and a spiral spring surrounding
the piston and secured at one end to a collar on the piston and surrounding and
secured at the other end to the cylinder.
Dated thin oth
T
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