Abstract: Extinguisher provided with a temperature compensated pressure controller, comprising a propelling agent and an extinguishing agent under gaseous form, wherein it comprises a sealed chamber filled with a mixture having a thermodynamic characteristic similar to that of the two agents in the extinguisher, a system for measuring the differential pressure exisiting between the inside of the sealed chamber and the chamber per se and a device actuated by the system for measuring the differential pressure and generating an alarm signal when the differential pressure exceeds a threshold value.

Abstract: An actual pressure of a fluid having an ambient pressure as part thereof is sensed by a sensor. When the actual pressure decreases below a predetermined pressure, a signal is produced. If desired, the sensor may cause production of the signal when the actual pressure of the fluid exceeds a predetermined pressure.

Abstract: A pressure-biased, temperature sensor means utilizing a cooperating pair of aligned bellows operators in a chamber communicating with a fluid system. One of the bellows expanding in response to an elevated temperature of said fluid and the second bellows expanding in response to a decrease in fluid pressure. Both of the bellows operate to move a diaphragm operator to close a switch means in a signal circuit thereby completing the circuit and energizing a signal means.

Abstract: A medium to high viscosity liquid flow detector and alarm sub-system for use with apparatus for automatic liquid dispensing machines for mastics, sealants, adhesives, and the like, comprising a liquid pressure sensing device disposed in the liquid flow path of the liquid dispensing gun of the machine. The liquid pressure sensing device derives an output electrical signal indicative of the instantaneous liquid pressure in the liquid flow path. A differentiating circuit differentiates the liquid pressure indicating signal to derive a rate of change in fluid pressure signal. The rate-of-change signal is supplied to an indicator for signalling the existence of an undesired rate-of-change in liquid pressure condition and is indicative of a bubble or void in the liquid mastic, sealant, or the like being dispensed.

Abstract: An arcing fault detector used the thermodynamic conditions created by an arcing fault within a vented electrical equipment enclosure to quickly activate a protective device which causes tripping of the supply circuit breaker(s). A plurality of temperature sensors are located within the enclosure near the top, and a differential pressure sensor is located in the external wall of the enclosure approximately midway between the vents to compare internal and external pressure. The intelligence from the sensors is processed by a fault protector which controls the tripping of the circuit breaker(s).

Abstract: By providing a pressure responsive actuator in controlled actuating engagement with a latch mechanism in which a spring-loaded indicator is securely retained, with said indicator being movable from a non-visible, retained position to a visible, released position in response to pressure exceeding a desired level, a unique, precision constructed pressure sensor and indicator is achieved. In the preferred embodiment, the latch mechanism comprises a plurality of elongated, resilient, spring-biased locking fingers, with the locking fingers being controllably disengaged from the indicator in response to the movement of the pressure responsive actuator. In addition, the present invention is also quickly and easily manually reset, thereby further enhancing the usability of the present invention.

Abstract: A pressure-temperature sensor for monitoring a fluid system for an over-temperature, an under-pressure or an over-pressure condition. The sensor includes a bellows operator enclosed in a fluid-filled housing with a normally-closed, first switch means and a normally-open second switch means. A diaphragm operator and a bellows are responsive to changes in temperature and pressure to, respectively, operate the first and second switches to indicate an over-temperature, an under-pressure or an over-pressure condition.

Abstract: The electronic recording manometer is intended particularly for the graphical representation of atmospheric pressure and for use aboard ship. A generator element (1,5,6) supplying pressure-equivalent electric pulses is connected to the input of a microprocessor (2). The microprocessor (2) is provided with a clock unit (8) and a memory unit in which a calendar is stored, and which records the measured pressure values for a predetermined length of time. The outputs (4, 7) of the microprocessor (2) are connected to a liquid crystal display (3) to provide digital pressure display and graphic representation of the march of pressure, as well as being connected to a visual and/or acoustic warning device. The warning device is actuated if the pressure rate of the pressure drop exceeds a value between 0.5 and 5 mb/hour. The clock unit (8) and the memory unit can be adjusted and/or called up by means of film keyboard elements (9).

Abstract: A window security device adapted for use in a vacuum environment. The device includes a conductive seal in electrical communication with an alarm. When the vacuum is disturbed the seal falls out of contact with the alarm circuit, activating the alarm.

Abstract: A differential pressure operated electrical switch construction is provided and has a housing carrying a pair of rigid terminals and an electrical switch for electrically interconnecting the terminals together under the control of an actuator that is responsive to differential pressure acting across the same. The terminals have free ends angled toward each other and the switch comprises a movable contact member and a spring operatively associated therewith for urging the contact member into bridging contact with the free ends of the terminals to thereby place the terminals in electrical contact with each other.

Abstract: A pressure-biased, temperature sensor for monitoring a fluid system for either an over-temperature or under-pressure condition. The sensor includes a bellows operator immersed in the fluid of a coolant system. The bellows operator expands in response to changes above a predetermined temperature or below a predetermined pressure to complete a signal circuit and energize a signal means.

Abstract: A pressure change sensor includes a flexible hollow body to receive pressure changes, an inner body in said flexible hollow body, the inner body being of a size less than and a shape different from the hollow of said hollow body to prevent total occlusion of the hollow body interior under pressure, and a fluid operated switch in fluid communication with the interior of the hollow body responsive to pressure changes applied to the hollow body.

Abstract: In a pressure measuring system which includes a pressure transducer for generating an analogue signal as a function of pressure, circuitry for generating a non-linear error signal as a function of the difference between the input signal and a feedback signal, a feedback circuit which generates the feedback signal as a function of said error signal to null the error signal and generates a digital output signal as a function of the pressure, a pressure surge detecting circuit having an amplitude detector connected to said pressure measuring system to receive the error signal and generating an output signal when the error signal is equal to and greater than a predetermined magnitude; a timer circuit connected to receive said output signal and generate an alarm signal when the output signal continues for a predetermined period of time, a digital computing circuit connected to receive the digital output signal for computing the rate of change of pressure and the change in pressure, a memory circuit storing predete

Abstract: Vacuum monitoring apparatus which includes a control circuit having transducer means for sensing the vacuum levels in a system and generating output signals. The control circuit includes adjustment circuits which compare the transducer output with selectively variable reference signals for controlling indicator devices and an alarm circuit when the vacuum levels are at respective high, low and normal settings. An off adjustment circuit is provided for setting the vacuum level below which the alarm circuit is disabled. A time delay circuit disables the alarm circuit for a predetermined time delay to provide for measurement of the vacuum recovery rate for the system.

Abstract: At least two magnetic-reed switches are mounted at spaced angular locations beneath the scale of a Bourdon-type pressure gage wherein the needle tip carries a permanent magnet. The reed switches change their respective states upon sensed-pressure descent to first and second predetermined levels of pressure, respectively indicative of different impending needs to switch a new container into the line of pressure delivery to beverage-dispensing apparatus. In one form, the impending needs reflect corresponding situations of remaining gas content of the cylinder, for room temperature storage and for cold-room storage, respectively; and a manual switch at the gage enables the gage to perform, as is appropriate for the particular situation of stored-container temperature. In another form, the second or additional magnetic-reed switch is positioned beneath the scale for operation upon a sensed low level of gas-pressure effectiveness for beverage dispensing.

Abstract: The atmospheric pressure actuated alarm of the present invention comprises a pressure transducer which senses the atmospheric pressure and produces an electrical transducer signal in response thereto. A difference amplifier is connected to the pressure transducer for measuring the transducer signal and for producing an output signal whenever the transducer signal is of a magnitude outside a predetermined range. An operational amplifier is connected to the difference amplifier for amplifying the transducer signal. A latch is connected to the operational amplifier for receiving the amplified signal. A signal alarm and a power source are connected in series with the latch. The latch is changeable from an open condition to a closed condition in response to the amplified signal being greater than a predetermined magnitude. When the latch moves to the closed condition, it connects the power source to the alarm signal and causes actuation of the alarm signal.

Abstract: In combination with a blood reservoir, a blood volume detecting apparatus is used to ensure safe operation of the reservoir which includes a conduit in fluid communication with a lower part of said blood reservoir, a diaphragm associated with the other end of the conduit and movable by a differential hydraulic pressure applied by the blood through the conduit, and means for detecting the swelling and contracting movement of the diaphragm.

Abstract: A pressure monitor is provided for gas pressure supplied to a patient. The monitor includes a pair of spaced contacts in the form of crank arms. A spring member is fixed at one end and is deflectable by a pneumatic cushion supplied with air from the gas supplied to a patient. The pneumatic cushion interacts with the resiliency of the spring member to urge the spring member to an intermediate position between a pair of fixed contacts. Too low a gas pressure will permit the spring member to engage one contact, while too high a gas pressure will cause the spring member to engage the other contact. Closure of the spring member against either contact energizes a respective alarm. In addition, there is provided a preset pneumatic-electrical switch connected to an oxygen supply line to indicate low oxygen pressure.

Abstract: A pressure control apparatus, which can be used for a braking force magnification apparatus for a vehicle or a door closing and opening apparatus includes a sensor for sensing a pressure within a vacuum booster. The sensor is of a transfer-contact-type including a medial movable contact and two stationary contacts. The movable contact makes contact with one of the stationary contacts connected to an alarm lamp but breaks contact with the other connected through a control circuit to a DC motor connected to a vacuum pump or a compressor when the absolute gauge pressure produced by the vacuum pump or compressor is below a first predetermined threshold value. The movable contact breaks contact with the one stationary contact to energize the DC motor when the absolute gauge pressure is below a second predetermined threshold value but is above the first one.

Abstract: A light-emitting indicator comprising: a housing having a longitudinal bore therethrough, a moveable member at least partially positioned within said bore, a light-emitting diode operable as a function of the position of the moveable member within the bore, a lens for displaying the light emitted from said light-emitting diode, and a bore provided in the upper portion of the moveable member for containing the light-emitting diode within the moveable member when the indicator is in its first operative position.

Abstract: An overdrive transmission for a motor vehicle has a housing with a rotatably mounted driving shaft and a rotatably mounted driven shaft. A planetary gear device is used to transmit power from the driving shaft to the driven shaft. In two of the illustrated embodiments, when the transmission is in the direct drive mode the planet gear carrier of the planet gear device is allowed to rotate and is engaged with the driven shaft by a clutch for power transmission at a 1:1 ratio, and when in the overdrive mode the planet gear carrier is prevented from rotation by another clutch and is disengaged from the driven shaft for power transmission to the driven shaft through the planetary gears of the planetary gear device at an increased gear ratio.

Abstract: A vacuum monitor for a vacuum interrupter which can detect poor vacuum pressure at high detection sensitivity from the outside of the interrupter, on the basis of the impulsive electromagnetic wave signals generated when vacuum pressure increases within the vacuum interrupter. The vacuum monitor according to the present invention comprises, in particular, a detector terminal of capacitor coupler type or inductor coupler type disposed near a high voltage conductor for receiving impulsive electromagnetic wave signals, a signal level discriminating section, and a diagnosis section for improving the reliability of the monitor, particularly when the detected signal level of the electromagnetic wave signals is low.

Abstract: Disclosed is a positive displacement pump output monitor which is employed by (a) passing the discharged fluid from said pump through a pulse receiving chamber, the pressure of said pumped fluid during the discharge stroke of the pump causing a diaphragm in said pulse receiving chamber to be moved outwardly by said fluid; (b) causing the outward concurrent movement of a spring-loaded metal shaft when the diaphragm is moved outwardly; (c) contacting a fixed element with said outwardly moved spring-loaded shaft, thereby causing a time-delayed relay connected to said fixed element to be reset; and (d) causing said time-delayed relay to send an alarm signal to an alarm annunciation means if said relay is not reset within a predetermined amount of time.

Abstract: An abnormally high vacuum pressure of a vacuum interrupter is detected from outside of the interrupter in response to electromagnetic wave signals generated by an electric discharge derived in response to a voltage difference and depending upon Paschen's law. Since the above-mentioned electric discharge is quite different from so-called partial discharge, even when the fixed and movable contacts are closed (i.e., under hot-line condition), it is possible to detect poor vacuum pressure on the basis of the electric discharge existing between the fixed and movable contact rods including two contacts and the main shield, as well as when the two contacts are open. The vacuum monitor according to the present invention comprises a rod or loop antenna fixedly or movably disposed near a conductive material of or connected to the vacuum interrupter and a detection section including, in particular, a 2 to 20 KHz band-pass filter.

Abstract: An asymmetric thrust warning system for an aircraft having two gas turbine engines. The compressor discharge pressures of the two engines are compared to determine the engine providing the lower thrust and to provide a signal indicative of the actual difference in thrust. If the difference in thrust exceeds a prescribed value related to aircraft altitude, a low thrust warning lamp is illuminated. In addition, the positions of the two augmenter metering valves are compared. If their positions significantly differ, the warning light associated with the valve having the minimum opening will be illuminated. A stall warning circuit may also be included as a part of the system.

Abstract: A device to be used in conjunction with oxygen cylinders or other gas cylinders which will sound a warning and/or flash a light when the gas supply is running low and the cylinder is in need of replacement. A pin is inserted through a lens which normally is placed over a gas gauge dial wherein the gauge dial has a standard indicator arm which moves when the pressure decreases. When the indicator arm moves, normally in a counterclockwise direction, it will make contact with the pin when the level in the tank has been reduced to a point where it should be replaced. This will then complete an electrical circuit which would cause an alarm to sound and/or a light to flash. The circuit comprises essentially two lead wires each connected to a battery with one of the leads connected to a metal part of the regulator and another lead connected to the pin associated with the gauge.

Abstract: An inductive pressure sensor is proposed which has at least one coil embodying a frequency-determining part of an oscillator and disposed at a distance from a diaphragm which is deflectable in accordance with pressure. When pressure is exerted on the diaphragm, the inductance of the coil and thus the oscillator frequency are shifted. The coil is a flat, spiral element and the diaphragm has a surface of highly conductive or ferrite material. It is further provided that two oscillators of identical design and having corresponding coils are used, operating under identical thermal conditions. Either one oscillator operates at a fixed frequency, so that both absolute-pressure measurements and differential-pressure measurements relative to ambient pressure can be made, or else the two oscillators can be detunable in accordance with pressure, so that differential-pressure measurements between two media can be made. The output signal is then obtained by mixing.

Abstract: A warning means for a safety valve of a hydraulic power unit and a hydraulic power unit having the same for use in a lifting jack, a vehicle lift, or the like, are disclosed. When an overload is given to a cylinder chamber of a hydraulic power unit, a safety valve is automatically opened so as to release an oil in the overloaded cylinder chamber back to an oil tank. When the safety valve is opened, a warning means switches on a caution buzzer and a caution lamp to appeal the overload to the senses of eyesight and hearing of a human being in order to prevent an accident to be followed previously. The warning means comprises a reed switch and a magnet adapted to be moved by the oil passed through the safety valve.

Abstract: A wheel-mounted tire pressure sensor employs a Bourdon tube which deforms in relation to tire pressure to drive a pivotal arm. Opposite ends of the arm support magnets which can close reed switches arrayed around the path of travel of the magnets. The reed switches are connected to passive resonators in such a way that for each of a number of regions of travel of the arm, a unique combination of resonators is activated. The resonators are connected to a wheel-mounted antenna which faces a stationary antenna. Frequency signal matching the frequencies of the resonator are sequentially broadcast by the stationary antenna to the resonators, which are excited to oscillate if activated by the corresponding switch or switches. The excited resonator broadcast their frequencies back to the stationary antenna and to a display unit which decodes the combination of resonator frequencies to display the corresponding tire pressure.

Abstract: A separate overload detecting and warning system for hydraulic jacks comprises a load sensing bypass pipe channel communicating with the high-pressure piping of the hydraulic jack, a linear load sensing unit directly connected to the load sensing bypass pipe channel for receiving the pressure signal therefrom, a warning circuit system having a multiple load-limit setting arrangement electrically coupled with the linear load sensing unit, and a power source switch mechanically connected with the release valve of the hydraulic jack and electrically connected to the warning circuit system for automatically energizing and de-energizing the warning circuit system along with the closing and opening of the release valve.

Abstract: A pump control system has a vacuum pump driven by a DC motor to supply a negative pressure to a container first power and driving transistors which are interconnected to energize the DC motor, second power and driving transistors which are interconnected to turn an alarm lamp on, and a pressure sensor having a set of normally closed contacts which are connected to the first driving transistor and which are connected via a Zener diode to the second driving transistor; the contacts opened by at least a predetermined negative pressure within the container so as to immediately turn the first power transistor off and so as the second power transistor off with a time delay as determined by a parallel combination of a capacitor and a resistor connected to the Zener diode.

Abstract: A device for detecting leaks of cryogenic materials from a structure, said device comprising a heat-conductive element which can be brought into contact with the cryogenic material-containing structure, and a shape memory effect element capable of effecting a displacement according to the cryogenic temperature to which the element is subjected.

Abstract: A tire pressure monitor which includes a signal generating section and a signal processing section. The signal generating section has a transducer which produces a first signal which is dependent on the tire pressure, and a transistor the collector current of which is controlled by the first signal. The signal generating section is supplied with power from a battery source and the current so supplied includes the collector current and is therefore dependent on the tire pressure. The signal processing section includes a monitor which monitors the supply current to the signal generating section and a display for providing an indication of the tire pressure.

Abstract: A vehicle, such as an agricultural tractor, includes a hydraulic assist-type transmission with fluid control and lubricating circuits. A monitoring system senses the fluid pressure in the lubricating circuit, the hydraulic fluid temperature and the engine speed. The sensed pressure is compared to a temperature and engine speed-compensated alarm value. Alarm signals are generated when the sensed pressure is continuously below the alarm value for a certain period. The alarm is disabled when the engine speed falls below a non-zero threshold level.

Abstract: An engine oil pressure monitor includes an engine oil pressure sensor and an engine speed sensor. A plurality of pressure alarm values are generated to correspond to designated distinct ranges of engine speed. One of the alarm values is selected according to which engine speed range contains the sensed engine speed. An alarm signal is generated when the sensed pressure falls below the alarm value. The alarm is disabled when the engine speed falls below a minimum non-zero engine speed and is disabled unless the pressure failure condition persists for at least a predetermined time period.

Abstract: A pressure transducer, such as a microphone, is placed in proximity to the blades of a fan, such as a fan used to cool electronic equipment. As each blade passes the transducer, a pressure wave is generated that is converted into an electrical pulse by the transducer. Circuitry responsive to those pulses signals an alarm if the fan is not operating properly.

Abstract: A control device in an anesthetic administering system which senses the dangerous condition of nitrous oxide flowing to the patient's breathing mask in the absence of oxygen flow to the mask and provides a warning signal so the condition is known and, thus, is correctable.

Abstract: Apparatus for rapidly achieving a desired pressure level in a tire by gas flow through a port in the tire such as the valve stem including a conduit having one end for connection to a source of gas under pressure and another end for connection to the inflation port. Valves are utilized for selectively closing and opening the conduit and for venting the conduit to the atmosphere. A selector whereby a desired pressure level to be achieved within the tire is provided as is a pressure level sensor which is connected to the conduit. A control in the form of a microprocessor digitally operates the valves to thereby provide for rapid inflation of the tire inasmuch as substantially full source pressure is applied to the tire to thereby provide a high pressure differential and increased gas flow.

Abstract: An improved alarm system sensing and triggering apparatus for remote detection of interruptions or alterations in an otherwise closed electrical alarm circuit. Exposed electrodes are embedded together with a substantially deformable current conducting element in a recessed housing cavity. The conducting element is compressable or deformable, momentarily, to an altered shape to activate the alarm system without the need for partially or completely detaching the sensor itself from the article to which it is connected. The recessed cavity together with the exposed electrodes and deformable conducting means cooperate with the sensor housing and alarm system integration conductors and with sensor attachment devices to provide the improved security features.

Abstract: An apparatus to continuously monitor a preset altitude for a pilot of an aircraft. It senses a change in altitude and an audible as well as a visible alarm tells the pilot that he has deviated from his preset altitude by a given height. Increase in altitude is signaled by a high pitch tone and by a yellow light while a decrease in altitude is signaled by a low pitch tone and a red light. The invention can also be used to warn a small boat operator of a pressure drop.

Abstract: A "snap action" early warning bypass valve assembly (2), responsive to fluid pressure differentials and/or low pressure, functions as both an electrical switch to provide an indication of low pressure or an impending fluid bypass and as a mechanical valve to actually implement the fluid bypass. The valve assembly includes a sealing piston (24, 124) supported by a retaining surface (18, 106) having a central bore (22, 110) formed therein. The sealing piston (24, 124) contains a bypass aperture (36) and is shaped to present a differential sealing area (39) to fluid circulating within the central bore (22, 110). A spring-biased bypass disc (42, 134) covers the bypass aperture (36) to present a central sealing area (45) to fluid within the central bore (22,110). A first pressure differential acting simultaneously across the central (45) and differential (39) sealing areas forces piston (24) into contact with an electrical terminal pin (48,92,126) thus energizing an alarm circuit (48-64,90).

Abstract: An overload detecting and alarm device for hydraulic jack comprises an electronic alarm device and a pressure sensitive switch member connected with the electronic alarm device. The pressure sensitive switch member is inserted into the body of the hydraulic jack and is communicated with the ram cylinder through a duct. This switch member comprises a pressure actuated piston which is normally biased in one direction and a spring plate positioned at another direction. The piston and spring plate act as electric contacts in the switch member and will come into contact each other when an overload fluid pressure is exerted on the piston, thereby inducing the electronic alarm device to produce a warning signal.

Abstract: A low fuel pressure monitor (25) for a two cycle engine (12) having an operating piston (21) initially cooled by pressurized fuel senses the fuel pressure at an output (18) of a fuel pump (14) and the operating speed of the engine (12) as sensed at an output (30) of an alternator (24) to provide an alarm (31) in response to a sensed low fuel pressure condition existing for a predetermined period of time while the engine (12) is operating above a predetermined speed. A circuit (99) senses an improper polarity connection of a battery (96) to provide a second type of an alarm.

Abstract: A capacitive pressure relief rupture disc monitor for use in detecting the rupture of an electrically conductive rupture disc installed in a pressure relief vent includes a flat metal loop positioned in spaced relation to the rupture disc and forming a capacitor therewith. A capacitance sensor is connected to the disc and the loop and is operative to generate an output signal in response to a selected change in the capacitance between the loop and the disc as a result of movement of portions of the disc during rupture thereof. The output signal from the capacitance sensor is operative to trigger an alarm to thereby indicate the rupture of the disc.

Abstract: The invention discloses a monitoring device for monitoring vacuum pressure of an electrical device employing an evacuated envelope. The invention provide, particularly, a pressure responsive monitoring device which comprises an electric field generating device of vacuum type, an electric field detector means including a light source for generating light, an electric field detector detecting change of the electric field of the electric field generator due to the change of vacuum pressure inside the envelope and controlling the light depending upon the change of the electric field, and photoelectric converter for converting the light controlled by the electric field detector to an electric signal which is employed to monitor the vacuum pressure of the envelope.

Abstract: An annunciator and/or shut-down system for an automatic processor for treating tissue specimens. In a tissue processor of the type wherein the reagents are drawn from reagent containers into the reaction vessel by drawing a vacuum on the vessel and reagents are returned to their respective reagent containers by gravity, the filled or unfilled condition of the reaction vessel is determined by sensing the vacuum condition during two time intervals; one near the start of filling and one just after filling is normally completed. The vacuum condition indicative of a filling or filled vessel differs for each sensing time interval. Logic circuitry analyzes the sensor condition for the specific time interval and, if the condition is maintained over a predefined delay period, outputs a short duration shut-down signal which causes latching of a mechanical shut-down and/or annunciator switch.

Abstract: Finely divided particulate solids are discharged from a high pressure zone to a low pressure zone, e.g. to atmospheric pressure, by passing a dense bed of this particulate material through a long discharge channel and past a throttle element. The pressure drop across the throttle element is significantly reduced due to the fact that the moving dense bed in the discharge channel dissipates the pressure drop along this channel leaving only a small pressure drop to be achieved across the throttle element.

Abstract: A differential pressure transducer is a body with a pair of opposed sensing chambers bounded by diaphragms and associated surfaces of the body. The surfaces have conducting layers and form capacitors with the metal diaphragms. The chambers are connected together and fitted with a fixed mass of oil. A signal generating circuit produces electrical signals representing the values of the two sensing capacitors which are fed to a computer to calculate the differential pressure independent of temperature.

Abstract: A pressure monitoring system for a high-voltage vacuum circuit interrupter including a plurality of capacitors connected in series located outside an evacuated housing and between two metallic end plates each attached to the electrode holder and an arc shielding member. The pressure monitoring system which monitors the deterioration of vacuum pressure within the evacuated housing of the interrupter by detecting the change in the electric field intensity of the capacitors dependent upon the change in vacuum pressure comprises a light source, at least one electric field detecting member having a Pockel's cell located on one of the capacitors, light receiving member and a vacuum pressure determining member, whereby an automatic monitoring of vacuum pressure within the evacuated housing of the vacuum circuit interrupter or within each of the evacuated envelopes of a plurality of vacuum circuit interrupters can be made.

Abstract: A "snap action" early warning bypass valve assembly (2) responsive to fluid pressure differentials functions as both an electrical switch to provide an indication at impending fluid bypass and as a mechanical valve to actually implement the fluid bypass. The valve assembly includes a piston (24) supported by a retaining surface (18,106) having a central bore (22,110) formed therein. The piston (24) contains a bypass aperture (36) and is shaped to present a differential sealing area (39) to fluid circulating within the central bore (22,110). A spring-biased bypass disc (42) covers the bypass aperture (36) to present a central sealing area (45) to fluid within the central bore (22,110). A first pressure differential acting simultaneously across the central (45) and differential (39) sealing areas forces piston (24) into contact with an electrical terminal pin (48,92), thus energizing an alarm circuit (48-64,90).