Abstract: The instant application pertains to new fluid level monitoring apparatus and a cooling system for computer components that employs the fluid level monitoring apparatus. In one embodiment, the liquid level measurement device comprises a load cell and a buoyancy element. The buoyancy element is configured to be partially submerged in the liquid phase. The load cell and the buoyancy element are operably connected such that a change in liquid volume may be determined using Archimedes' principle.

Abstract: A system for detecting a characteristic of a fluid. In one example, the system includes a tube, a float, a sensor, and a controller. The tube is configured to receive the fluid. The float is located within the tube. The sensor is configured to sense a position of the float. The controller is configured to receive, from the sensor, the position of the float, and determine a characteristic of the fluid based on the position of the float. The characteristic may be a density or a concentration.

Abstract: Apparatus and method for a physical simulation experiment of fracturing an unconventional oil and gas reservoir layer by layer by spiral perforation via a horizontal well bore. The apparatus includes an outer wellbore provided with at least three layers of spiral perforations, and an inner wellbore provided with at least three layers of through-holes. The method includes injecting fracturing fluid into the inner wellbore, and opening a first layer cracks of a stratum by the fracturing fluid passing the first through-hole layer and the first spiral perforation layer, opening a second layer cracks of the stratum by the fracturing fluid passing second through-hole layer and second spiral perforation layer and opening a third layer cracks of the stratum by the fracturing fluid passing third through-hole layer and third spiral perforation layer.

Abstract: A density meter for measuring the density of a fluid, having a base plate, wherein a spring element is clamped to the base plate; a torpedo, wherein the torpedo comprises a known weight, and wherein the torpedo is attached or coupled to the spring element; and a sensor, wherein the sensor measures a deflection of the spring element, as the torpedo displaces a volume of fluid.

Abstract: A density measuring device is described having: a housing, internally defining a first chamber, designed to contain a fluid the density of which it is desired to measure, and housing, in a measurement operating condition, a float, designed to be immersed in the fluid; and an electronic circuit that detects a value of the density as a function of a thrust sustained by the float due to the effect of the fluid; the housing further defines a second chamber, designed to contain a filling gas and to house the float in a cleaning operating condition of the float, distinct from the measurement operating condition, for removing gas bubbles and/or solid particles that have adhered to an outer surface of the float during the measurement operating condition.

Abstract: A radiator detecting device of the present invention includes a radiator cap, a sensing unit, a circuit device, a warning device, and an adjusting means. One end of the sensing unit connects to the radiator cap, and another end extends toward a direction away from the radiator cap. The circuit device has a circuit board. The circuit board includes a control circuit for detecting a state of the sensing unit, and the sensing unit selectively makes the control circuit generate a suggestion signal. Once receiving the suggestion signal generated by the control circuit, the warning device generates a warning signal. The adjusting means is used for adjusting a length of the sensing unit received in the radiator. Said sensing unit can be moved with respect to the radiator between a first position and a second position. Thereby, the sensing unit can fit different depths of different radiators.

Abstract: An assembly for measuring both the level and specific gravity of a liquid in a container includes a first sensor arrangement for sensing the level of the liquid in the container, and a second sensor arrangement for sensing the specific gravity of the liquid. The first sensor arrangement measures and then independently outputs at least one signal relating to the liquid level in the container. The second sensor arrangement measures and then independently outputs at least one signal relating to the specific gravity of the liquid in the container, thereby providing an integrated device to measure both parameters of the liquid.

Abstract: A device for determining the density of a fluid comprises a buoyant body, a spring which engages on the buoyant body and whose elastic deformation is a measure of the buoyancy force of the buoyant body, and a magnet which is designed to sense the elastic deformation of the spring by means of a magnetostrictive position-measuring system. The spring is compressively loaded and, if the buoyancy force of the buoyant body is greater than its weight, said spring acts on the buoyant body underneath its centre of buoyancy. The device is preferably used to determine the density of fuel, a magnetostrictive filling level measuring system which is present in a storage tank for fuel being used.

Abstract: An injection molded plastic rod suitable for use in a battery hydrometer. Stress-relieving formations are provided symmetrically arranged on opposite sides of an injection gate of the rod. The formations distribute injection stresses and shield the gate vestige.

Abstract: A liquid density/liquid level meter includes a spring-float system that is coupled with a multiple Hall-sensor configured linear displacement transducer. The spring-float system includes springs that constrain the movement of floats on each end; the spring-float system parameters are mathematically evaluated so as to meet precise performance criteria. The linear displacement transducer includes a magnet and the Hall sensors. The linear displacement transducer and the spring-float system are coupled together within a submersible head unit. When the head unit is immersed in the liquid, the spring-float system moves the magnet, which interacts with the Hall sensors in a lateral slide-by approach that produces an analog voltage that is continuous and linear with respect to the displacement of the magnet. The output from the head unit is communicatively connected to a remote electronic module that contains a signal conditioner with a digital readout.

Abstract: A plurality of test chambers or fixtures are operable for successively testing a plurality of condoms, respectively, in an automated manner. Each test chamber for testing a condom includes a housing containing a porous liner having an interior cavity conformed to the exterior shape of a condom to be tested, whereby a holder carrying the condom is inserted into the liner, a closed pathway for gas flow is provided between a gas port of the holder and the interior volume of the condom, for permitting the condom to be inflated with the gas, causing the exterior walls of the condom to be pushed against opposing inside walls of the liner, permitting gas passing through holes in the condom to flow through pores in walls of the liner to another gas port of the housing for detecting unacceptable holes in the condom using differential pressure techniques and/or gas tagging.

Abstract: An sensor for sensing buoyancy force within a liquid mixture stored within a storage tank and an interlock employing the sensor to prevent a respirable cryogenic mixture from being dispensed from the storage tank with an unsafe oxygen content. The sensor has a float adapted to be submerged in the liquid mixture, thereby to exert a buoyancy force referable to the density. The buoyancy force is sensed by a load cell connected to an elongated base element cantilevered from the outlet by a bracket. The mounting of such sensor ensures that the buoyancy force and therefore, the density of the liquid as dispensed will be measured as opposed to liquid density at some other location of the tank. Such sensor can serve in an interlock in which a controller responsive to the load cell and a temperature sensor, also located within the outlet, controls a valve to close the outlet when the mixture has an unsafe oxygen level.

Abstract: A sensor for sensing buoyancy force within a liquid mixture stored within a storage tank and an interlock employing the sensor to prevent a respirable cryogenic mixture from being dispensed from the storage tank with an unsafe oxygen content. The sensor has a float adapted to be submerged in the liquid mixture, thereby to exert a buoyancy force referable to the density. The buoyancy force is sensed by a load cell connected to an elongated base element cantilevered from the outlet by a bracket. The mounting of such sensor ensures that the buoyancy force and therefore, the density of the liquid as dispensed will be measured as opposed to liquid density at some other location of the tank. Such sensor can serve in an interlock in which a controller responsive to the load cell and a temperature sensor, also located within the outlet, controls a valve to close the outlet when the mixture has an unsafe oxygen level.

Abstract: A method and apparatus for monitoring characteristics of a fluid contained in a vessel includes a fluid displacer suspended in the vessel. The buoyant force acting on the fluid displacer is measured using a pair of force transducers and used to calculate fluid characteristics such as the height of the fluid in the vessel, fluid density, solute concentration, and/or the presence of fluid cascading from one section of the vessel to another.

Abstract: A method and apparatus for monitoring characteristics of a fluid contained in a vessel includes a pair of triangular fluid displacers suspended in the vessel. The buoyant forces acting on the fluid displacers are measured using force transducers and used to calculate fluid characteristics such as the height of the fluid in the vessel, fluid density, solute concentration, and/or the presence of fluid cascading from one section of the vessel to another.

Abstract: A conveyor line conveys plural containers. A first sampler means moves the containers to a position at which a leaking liquid inspection apparatus is provided. A second sampler moves the containers to a position at which the entering air inspection apparatus is provided. A first stopper interrupts the containers at a position of the first sampler. A second stopper interrupts the vessels at a position of the second sampler. A third stopper is provided on the upstream side of the first and second stopper.

Abstract: A leak detection device includes a container-rotating disc mounted for rotation about a rotation axis. Multiple container-supporting test heads are mounted to the disc for rotation about the rotation axis. Each test head includes a sealing assembly supported by a first cam follower and comprising a cylinder, and a piston supported by a second cam follower and received in the cylinder. First and second annular cams are mounted above the disc to operate the first and second cam followers, respectively, such that the sealing assemblies and the pistons are moved between respective upper and lower positions as the disc rotates with respect to the cams. The cams are shaped to press the sealing assemblies against the containers, to raise the pistons to draw a partial vacuum in the containers, and then to lift the sealing assemblies and any sealed containers for a vacuum test. An improved seal accommodates a wavy upper surface of the container.

Abstract: A warning system alerts a driver of a motor vehicle to different types of traction losses. A first sensing circuit (10) detects a loss of wheel adhesion by monitoring a vehicle drive line for a pronounced vibration within a range of between ten and fifteen hertz. A second sensing circuit (12) monitors a brake light circuit to detect application of a vehicle brake. A logic circuit (28) combines outputs (A and B) from the first and second sensing circuits and outputs command signals (C and D) that distinguish between a loss of wheel adhesion due to wheel skidding and a loss of wheel adhesion due to wheel slipping. A warning device includes two indicators (36 and 38) that receive the respective command signals and produce sensorially distinguishable warning signals for eliciting different responses from the driver.

Abstract: A density measuring device having a float with a marker provided therein that is connected by a pair of springs to each of the two supports which are on opposite sides of the float along a guide. A sonic waveguide arrangement is provided extending along this guide past at least one of the supports which can measure the relative positions of the float to thereby determine the effective buoyant force on the float and so the density of the fluid in which the float is submerged. Use of a further float permits determining fluid levels.

Abstract: A density measuring device having a float with a marker provided therein that is connected by a pair of springs to each of the two supports which are on opposite sides of the float along a guide. A sonic waveguide arrangement is provided extending along this guide past at least one of the supports which can measure the relative positions of the float to thereby determine the effective buoyant force on the float and so the density of the fluid in which the float is submerged. Use of a further float permits determining fluid levels.

Abstract: A simple and mechanically-rugged calculation or monitoring of the density of fluids, particularly of fuels serving the purpose of driving an internal-combustion engine, provides that a buoyant member is immersed into the fluid under examination, the buoyancy thereof being balanced out via a load applied with a spring. A capacitor that is dependent on the buoyancy and, therefore, on the density of the fluid under examination is formed between the buoyant member and the housing that holds the spring and is filled with the fluid under examination, the capacitor being monitored via a circuit arrangement.

Abstract: A device for testing and withdrawing seals from manufacturing molds, which device consists of a pneumatic pickup member having a front impression connected to a pneumatic line in turn connected to a vacuum source, and defined by opposite edges designed to cooperate with respective peripheral sealing portions of each seal; the pneumatic line presenting a transducer for emitting a signal when the difference in the pressures detected on the line over a predetermined time interval exceeds a predetermined threshold value.

Abstract: A positioning cylinder assembly for subterranean mining applications has a rotary potentiometer connected through a friction wheel transmission with the spindle of the cylinder which is rotated when the piston is axially displaced therein. The friction wheel assembly comprises a pinion wheel connected to the spindle and a hollow wheel connected to the rotary potentiometer, that not only matches the pitch of the spindle to the rotary spring of the potentiometer but also functions as a slip clutch for zero setting of the potentionmeter and the piston.

Abstract: A vehicle anti-freeze monitor for monitoring the capability of the vehicle's coolant mixture in the cooling system of the vehicle to resist freezing. The monitor includes a light emitting diode, a reed switch for coupling the indicator to a source of electricity and for selectively activating and deactivating the indicator. Also included is a float for submersion into the vehicle's coolant mixture. The float includes a buoyant body and a magnet which activates the reed switch when the vehicle's coolant mixture is in a safe condition against freezing and deactivates the reed switch when the coolant mixture is in an unsafe freezable condition.

Abstract: A liquid level detector of the type in which a magnetostrictive wire extends through the liquid level measurement range and is captured in a tensioned vertical orientation within a stainless steel tube. Liquid level is measured as a function of the time required for a torsional disturbance imparted the wire near the top to travel along the wire to a magnet which is contained within a liquid level float which slides up and down along the tube. The torsional disturbances imparted to the wire by means of a piezoelectric crystal to which the wire is easily clamped. Accuracy is enhanced by measuring liquid level as a function of the elapsed time between an actuation signal and the first zero crossing of the voltage which is induced as the torsional strain passes through the area of influence of the sliding magnet.

Abstract: A stability meter comprises a translational accelerometer (1) which has a working axis along which it is sensitive to gravity. The meter is mounted on a vessel with the working axis horizontal when the vessel is in the upright position such that it transmits signals proportional to the sine of the angle of roll of the vessel to a microprocessor based apparatus (2). A microprocessor (12) conducts a Fast Fourier Transform on a plurality of samples from the accelerometer (1) in order to determine the dominant rolling frequency. The apparatus (2) comprises a display (8), a printer (9), a keyboard (10), a clock (14) and memory unit (16). The dominant rolling frequency is used to calculate the transverse metacentric height of the vessel. The value of the transverse metacentric height is transmitted to the display (8) as a measure of the stability of the vessel.

Abstract: A liquid level detector of the type in which a magnetostrictive wire extends through the liquid level measurement range and is captured in a tensioned vertical orientation within a stainless steel tube. Liquid level is measured as a function of the time required for a torsional disturbance imparted the wire near the top to travel along the wire to a magnet which is contained within a liquid level float which slides up and down along the tube. The torsional disturbances imparted to the wire by means of a piezoelectric crystal to which the wire is easily clamped. Accuracy is enhanced by measuring liquid level as a function of the elapsed time between an actuation signal and the first zero crossing of the voltage which is induced as the torsional strain passes through the area of influence of the sliding magnet.

Abstract: An affinity type gravity measurement instrument which is composed of material such as wood having a coefficient of thermal expansion. Within an internal cavity defined within the housing is disposed a quantity of liquid and a float partially submerged in the liquid. The liquid and float have low coefficients of thermal expansion. The housing defines an internal temperature compensation cavity receiving liquid upon expansion thereof to thus minimize change in the height of the liquid column and thus change in the position of the float and target response to temperature change. A stem of the float extends through an opening at the upper portion of the housing and supports a target, the position of which is sensed by an eddy current, laser or radar proximity sensor, developing signals which are processed for digital readout and computer processed for mapping.

Abstract: A process for the continuous measurement of the density of a liquid by means of an aerometer body swimming in the liquid is characterized by the feature that the liquid is allowed to flow periodically at an increased flow rate past the aerometer body in order to clean the same of foreign matter, gas bubbles or the like disturbing the measuring, with the measuring procedure being interrupted during this cleaning period. In an apparatus for performing this process, an aerometer body is surrounded in a measuring vessel by a partition wall at a small distance therefrom, and line is provided, through which liquid to be measured may be introduced at a relatively high flow rate into the space between the aerometer body and the partition wall in order to periodically clean the aerometer body.

Abstract: The present invention relates to a device for detecting the level of liquid in a tank. The device comprises a level detector formed of two arms pivoted on a common fixed support about first, respectively parallel, generally horizontal axes and a movable support member carrying a float adapted to follow the level of the liquid, the support member being pivoted on the two arms about second axes respectively spaced from but generally parallel to the first axes, in order that on change of level of the liquid the float follows a curved path determined by the combined pivoting of the arms, the float cooperating with a transducer adapted to generate a signal representing the position of the float.

Abstract: In the case of an apparatus for ascertaining and keeping constant the concentration of alcohol in the plate dampening fluid used in an offset litho press, having a float vessel with an inlet and an overflow such that the float controls the supply of alcohol in accordance with its level relative to the fluid, a high degree of accuracy and a simple possibility of displaying and storing the concentration data is made possible by having a marker mounted on the float and having a vertical scale of zones marked thereon which may be sensed without mechanical contact by a sensing device at a fixed height. Furthermore the sensing device has a control signal output connected with a controller which is furthermore acted upon by a set point signal and has at least one output signal connection for controlling a valve regulating the supply of alcohol to said fluid.

Abstract: Method of adjusting a concentration of oil in a water-containing oil material which comprises determining a change in buoyancy exerted on a plummet suspended in the oil material and controlling the amount of water being supplied to the oil material according to the change in buoyancy, and apparatus therefor.

Abstract: A density sensor includes a stationary housing (12) and a reciprocating body (22) with a float (26) attached thereto to provide a buoyant force. The reciprocating body (22) is connected to a piston (32) by a reciprocating rod (34). The piston (32) is operable to move within a bore (30). A second piston (52) is also disposed in the bore (30) and is coupled to the piston (32) by a spring (54). A transducer (44) is disposed at the other end of the bore and is connected to the piston (52) through hydraulic fluid disposed in a hydraulic chamber (56). The spring (54) is functional to remove low frequency components of acceleration from the buoyant force and the hydraulic fluid disposed in the hydraulic chamber (56) is operable to remove high frequency acceleration components from the buoyant force. In this manner, the transducer (44) can be isolated from both high and low frequency acceleration components.

Abstract: An ink liquid supply system for an ink jet system printer includes a sub tank for introducing a new ink liquid from an ink liquid cartridge and an old ink liquid from a beam gutter included in the ink jet system printer. A float element is disposed in the sub tank, the float element having a specific gravity of, for example, 1.062 which is slightly greater than the specific gravity of a preferred ink liquid suited for the ink jet system printer. In the normal operation mode, the float element is positioned at the bottom of the sub tank. When the ink liquid viscosity increases, the float element moves upward. A detection unit is associated with the float element to develop a control signal when the float element moves upward. In response to the control signal, a dilution is added to the ink liquid contained in the sub tank in order to reduce the viscosity of the ink liquid.

Abstract: An electronic hydrometer for determining the density of a liquid, the hydrometer comprising a housing having a liquid receiving chamber and means to insert a liquid of which the density is to be determined in the chamber. A float having a known weight is disposed in the chamber. A connecting shaft is secured to the float and retained for guided displacement along its longitudinal axis in response to introduction of a predetermined quantity of liquid in the chamber. A sensor is associated with a shaft for detecting a reference position of the shaft. A permanent magnet is mounted in proximity of the shaft and has a magnetic core and a displaceable coil about the core. The coil is secured to the shaft. An electronic circuit means automatically adjusts the value of a current flowing in the coil to displace the coil and the shaft relative to the reference position. The value of the adjusted current is calibrated by the circuit to generate an output signal indicative of the density of the liquid in the chamber.

Abstract: There is disclosed a battery hydrometer for providing an analog electrical signal having a magnitude related to the specific gravity of a battery electrolyte. The hydrometer includes a source of radiation for providing a detectable beam of radiation and a piston member arranged to be submerged within the electrolyte and to intercept and modulate the beam of radiation in response to the specific gravity of the electrolyte. The piston member is suspended within the electrolyte by a spring which exerts a compressive force upon the piston member against which the electrolyte must act. The hydrometer further includes a radiation detector aligned with the radiation source for providing an analog electrical signal having a magnitude responsive to the modulated beam of radiation.

Abstract: A device for indicating changes in the specific gravity of a liquid comprises first and second floats adapted to float on the surface of the liquid, the float having different shapes and/or densities so that the depth of the floats in the liquid varies in accordance with the specific gravity of the liquid and means for producing an electrical signal dependent upon the depth to which the floats are immersed relative to one another.

Abstract: A volumetric fuel meter is included in a fuel system whereby the measurement is compensated to express fuel flow in units of weight such as pounds, grams or in units of energy such as BTU's or calories (grams). The meter measurement is associated with an automatic compensator which compensates the measurement for variations in the gravity of the fuel. Temperature and pressure sensing devices are associated with the measuring systems. Two separate measuring systems are employed for engine fuel systems which return unburned fuel from the injector. One system employs a single volumetric meter with a bubble remover or cooler while the second system employs two volumetric meters. The present measuring system has embodiments that provide for mechanical compensation and electrical measurement and subsequent compensation of the gravity of the fuel.

Abstract: A method and apparatus for measuring the specific gravity of liquids in process streams by intermittently sampling the process stream and measuring the specific gravity of the sampled liquid under static conditions in a constant level overflow device by the use of a variable immersion hydrometer operatively connected to a linear voltage displacement transducer, i.e. differential transformer, whereby vertical displacement of the hydrometer results in an output voltage signal indicative of the specific gravity of the sampled liquid. Means can be provided for compensating the specific gravity for ambient and liquid temperature and for controlling and recording the specific gravity of the liquid.

Abstract: Apparatus and method for detecting and correcting for evaporation from recirculated unused ink drops in an ink jet printer. The specific gravity of the recirculating ink is compared with that of a standard by measuring the time of fall of heavy floats through reservoirs of circulated and uncirculated fluid. A significant difference in fall times is compensated by the replenishment of fluid in the recirculating ink supply.

Abstract: Apparatus for checking the valves of aerosol containers for tightness, in which a vacuum is produced under the valve being checked by pressing the valve by its shut-off member in the open position against a resilient member on a seat in order to deform the resilient member which, after removing the force of pressing and closing the valve, tends to return to the initial position, thereby increasing the volume of the cavity under the valve. This permits reducing the time of exposing the valve to the vacuum. The seats are made blind and are arranged on an endless conveyor which moves the seats with the valves to the mechanisms effecting the operations.

Abstract: A cigarette filter attachment machine comprises means for joining filter portions to cigarette portions by rolling adhesive-coated paper around adjacent parts of corresponding filter and cigarette portions, a conveyor for conveying the completed assemblies at regular intervals, a stationary pressure chamber adjacent to the conveyor and arranged to communicate successively with ports in the conveyor which are closed by the completed assemblies, a source of pressure connected to the pressure chamber, and a detector for monitoring the pressure in the chamber to detect the absence of any assembly.

Abstract: A warning system for indicating a critical charge condition of starter batteries in vehicles, especially in motor vehicles which operate according to the hydrometer principle; a specially constructed float is movably arranged on the inside of an areometer housing connected with the inside of the battery housing by way of apertures in such a manner that a warning signal is adapted to be triggered when the float sinks to a predetermined height corresponding to a predetermined acid concentration.

Abstract: A device for detecting the overdischarge of the accumulator as well as the surface level of electrolyte contained in the accumulator comprising a floating member, a case housing the floating member and having a hole through which the electrolyte in the accumulator passes, a means for sucking the electrolyte through the hole into the case, and a magnetically sensing switch arranged to be operated responding to movement of the floating member. At least one chamber communicated with the outside of the case is provided in the case outside the hole through which the electrolyte passes.

Abstract: An improved method and apparatus for measuring fluid flow and controlling fluid flow systems. The invention uses a magnetically responsive float normally resting in contact with a stop element positioned in the flow conduit, with magnetic means positioned upstream. The requisite increase of magnetic force to pull said float element from the stop element against the direction of fluid flow is related to the flow rate, thus serving to indicate same for metering or control purposes. Normally, the current to an electromagnet required to overcome the force of fluid flow is used as a measure of flow rate. This system can also be employed to determine fluid viscosity.

Abstract: A device for detecting the specific gravity and level of liquid in a container comprising a light source, a photoelectric transducer positioned in light receiving relationship with respect to the light source, a float which has a predetermined specific gravity and is displaced depending upon the change in specific gravity and level of the liquid, and means operatively coupled to the float so as to permit or interrupt the light transmission from the light source to the photoelectric transducer.

Abstract: A device for measuring the density of liquids. A float provided with a piece of soft iron on one side and with a permanent magnet on the other side is movably disposed in a housing through which a liquid may flow. The soft iron is surrounded by a differential winding, and the permanent magnet is surrounded by two windings with opposing fluxes and having substantially the same numbers of ampere-turns. An output lead from the differential winding is connected to the windings surrounding the permanent magnet over an amplifier. A measuring instrument connected between the amplifier and the windings surrounding the permanent magnet provides an indication of the density of the liquid flowing through said housing.

Abstract: A densimeter utilizes a low mass, neutral buoyancy float in association with a precision transducer which sense the deviation of the float position from a fixed neutral point corresponding to a predetermined fluid density within a range of fluid densities to be measured. The sensor output is accumulated and digitally added to a number corresponding to the predetermined density to thereby form an accurate representation of the fluid density.

Abstract: A system for accurately controlling the density of liquids in a processing system employing a chamber having a finned hydrometer with control activation mechanism floating in a reservoir of continuous sample solution, and having a plurality of chambers so constructed so as to create a liquid stream feeding the zone containing the hydrometer and imparting rotational motion thereto. The height of the hydrometer is sensed as measuring the density of the liquid sample. Appropriate corrections are made to the processing system.

Abstract: A system for testing opening-equipped containers for leakage during the entire period, which is usually relatively long, between the time that such containers are fabricated by the manufacturer thereof and the time that they are filled by the user with the product intended therefor. The system includes a testing method, a particular test closure or cap and structural relationship thereof with a container opening, and apparatus for establishing a pressure differential between the interior and exterior of any container under test.