Fluid testing device, and a method of testing a pressurized fluid for dissolved and/or entrained gasses

A method of testing a pressurized liquid fluid for dissolved gasses includes evacuating both a first tank and a second tank. A test volume of a pressurized liquid fluid is introduced into the first tank. An initial absolute pressure in the second tank is sensed, and then fluid communication between the first tank and the second tank is opened to allow the pressurized fluid to flow from the first tank into the second tank, thereby de-pressurizing the fluid. The de-pressurized fluid in the second tank is maintained for a pre-defined out-gassing period, to allow any gasses in the de-pressurized fluid to separate from the de-pressurized fluid. A final absolute pressure in the second tank is sensed. A difference between the final absolute pressure and the initial absolute pressure is correlated to a volume of gasses released from the de-pressurized fluid.

TECHNICAL FIELD

The disclosure generally relates to a fluid testing device, and to a method of testing a pressurized hydraulic liquid fluid for dissolved and entrained gasses with the fluid testing device.

BACKGROUND

Liquid fluids used in pressurized, hydraulic systems, should be absent of gasses, e.g., air, and/or water for optimal performance. Often, the hydraulic fluid will be processed prior to installation in the hydraulic system, in order to remove any gas and/or water contamination from the hydraulic fluid. The degree to which water is removed from the hydraulic fluid may be measured by an equilibrium reflux boiling point test. However, a test procedure for determining the degree to which gasses are removed from the liquid fluid, and particularly dissolved gasses, does not currently exist.

Entrained gasses in the hydraulic, liquid fluid, and particularly entrained air, may be detected through measurement of variation in density of the fluid by several methods or by visual inspection, and may appear as gas bubbles in the fluid. Entrained gasses in the liquid, hydraulic fluid, e.g., air bubbles in the fluid, negatively affect the performance of the hydraulic fluid in the hydraulic system due to the relative compressibility of the gas. Dissolved gasses in the hydraulic fluid are not visually detectable, and may not significantly affect the operation of the hydraulic fluid in the hydraulic system. However, a change in temperature and/or pressure of the fluid may cause any dissolved gasses in the hydraulic fluid to separate from the liquid hydraulic fluid, introducing entrained gasses into the hydraulic fluid, i.e., gas bubbles. Accordingly, it would be advantageous to be able to test the hydraulic fluid, at the condition (temperature/pressure) it may be delivered, with the gasses still in the dissolved state, in order to determine the degree to which gasses have been removed from the hydraulic fluid.

SUMMARY

A method of testing a pressurized fluid for dissolved and entrained gasses with a fluid testing device is provided. The fluid testing device includes a first tank having a first volume, and a second tank in fluid communication with the first tank and having a second volume. The second volume of the second tank is larger than the first volume of the first tank. The method includes connecting an evacuation and fluid filling system to the first tank, and evacuating both the first tank and the second tank with the evacuation and fluid filling system to form a vacuum in both the first tank and the second tank. Fluid communication between the first tank and the second tank is then blocked. A test volume of a pressurized fluid is introduced into the first tank, with the evacuation and fluid filling system. An initial absolute pressure in the second tank is sensed with an absolute pressure sensor. Fluid communication between the first tank and the second tank is then opened, to allow the test volume of the pressurized fluid to flow from the first tank into the second tank, and de-pressurize the fluid. The test volume of the de-pressurized fluid in the second tank is maintained for a pre-defined out-gassing period, to allow any dissolved or entrained gasses in the test volume of the previously pressurized fluid to separate from the liquid due to exposure to a deep vacuum. After the test volume of the now de-pressurized fluid has been maintained in the second tank for the pre-defined out-gassing period, a final absolute pressure in the second tank is sensed with the absolute pressure sensor. A difference between the final absolute pressure and the initial absolute pressure is correlated to a volume of gasses released from the test volume of the fluid.

A fluid testing device is also provided. The fluid testing device includes a first tank having a first inlet and a first outlet, and a fluid coupler attached to the first inlet. The fluid coupler is operable to connect the first inlet to an evacuation and fluid filling system. An inlet valve interconnects the first inlet and the fluid coupler. The inlet valve is operable to open fluid communication between the first inlet and the fluid coupler, and to also block fluid communication between the first inlet and the fluid coupler. A second tank includes a second inlet and a second outlet. The second inlet of the second tank is disposed in fluid communication with the first outlet of the first tank. A transfer valve interconnects the first outlet of the first tank and the second inlet of the second tank. The transfer valve is operable to open fluid communication between the first outlet and the second inlet, and to also block fluid communication between the first outlet and the second inlet. A drain valve is attached to the second outlet. The drain valve is operable to open fluid communication between the second outlet and atmospheric pressure, and to also block fluid communication between the second outlet and atmospheric pressure. An absolute pressure sensor is attached to the second tank. The absolute pressure sensor is operable to sense an absolute pressure within the second tank.

Accordingly, the fluid testing device enables the method of testing the pressurized fluid to determine an amount of dissolved gasses, e.g., air, in the pressurized fluid. The fluid testing device and method described herein enable a manufacturer to test and/or evaluate fluid processing techniques/processes for troubleshooting and/or quality performance purposes, which aid in the manufacturing processes utilizing the pressurized fluid.

DETAILED DESCRIPTION

Those having ordinary skill in the art will recognize that terms such as “above,” “below,” “upward,” “downward,” “top,” “bottom,” etc., are used descriptively for the figures, and do not represent limitations on the scope of the disclosure, as defined by the appended claims.

Referring to the Figures, wherein like numerals indicate like parts throughout the several views, a fluid testing device is generally shown at20. The fluid testing device20is operable to test a pressurized fluid22for dissolved and/or entrained gasses, such as but not limited to air. The pressurized fluid22includes a liquid, such as but is not limited to, a brake fluid, or some other liquid fluid intended for use in a hydraulic system. However, it should be appreciated that the fluid testing device20may be used to test any liquid fluid that is under pressure greater than atmospheric pressure, for a dissolved or entrained gas content. As used herein, the term “fluid” often, but not exclusively, refers to the liquid test sample proper, even though the term “fluid” may technically include a substance in either a liquid or a gas phase.

Referring toFIGS. 1 through 8, the fluid testing device20includes a first tank24and a second tank26. The first tank24includes a first inlet28, and a first outlet30. The second tank26includes a second inlet32, and a second outlet34. As used herein, the terms “first” and “second” are used as adjectives to identify respective components and/or features of the fluid testing device20, and are not intended to denote a relative quantity or number unless specifically noted herein. Accordingly, unless specifically noted herein, the terms “first” and “second” should not be interpreted to imply a number more than one.

The first tank24is disposed vertically above the second tank26, i.e., the first tank24is disposed at a higher relative elevation than the second tank26. The first inlet28is disposed at or near an upper vertical surface of the first tank24, and the first outlet30is disposed at or near a lower vertical surface of the first tank24. Accordingly, the first inlet28is disposed at a higher elevation than the first outlet30. The second inlet32is disposed at or near an upper vertical surface of the second tank26, and the second outlet34is disposed at or near a lower vertical surface of the second tank26. Accordingly, the second inlet32is disposed at a higher elevation than the second outlet34. This over/under or above/below configuration of the first tank24and the second tank26, as described above, is needed in order to assure gravity assist in the complete transfer of the fluid22during the test process to assist the fluid motion which is provided by the pressure differential between the first tank24and the second tank26when hydraulic communication between the first tank24and the second tank26is enabled as a necessary part of the test process.

A fluid coupler36is attached to and disposed in fluid communication with the first inlet28. The fluid coupler36is operable to connect the first inlet28to an evacuation and fluid filling system38. The evacuation and fluid filling system38may include any system that is capable of evacuating a closed volume to form a vacuum therein, and supplying the pressurized fluid22under pressure into the closed volume after the closed volume has been evacuated. The evacuation and fluid filling system38supplies the fluid at a pressure that is greater than atmospheric pressure. Evacuation and fluid filling systems38are common in manufacturing processes and known to those skilled in the art. As such, the specific configuration and/or operation of the evacuation and fluid filling system38is not described in detail herein. The fluid coupler36may include any coupler capable of connecting to the evacuation and fluid filling system38, and maintaining both a gas and liquid tight seal. For example, if the evacuation and fluid filling system38is configured for supplying a brake fluid to a vehicle during maintenance or manufacture of the vehicle, then the fluid coupler36may include an opening with specific geometric dimension that may be common to a vehicular brake master cylinder opening detail, such as known to those skilled in the art. However, it should be appreciated that the fluid coupler36may be configured in any suitable manner, and is not limited to any specific embodiment.

The fluid testing device20includes an inlet valve40, which interconnects the first inlet28and the fluid coupler36to control fluid flow between the fluid coupler36and the first tank24. The inlet valve40is operable or controllable between an open position and a closed position. When disposed in the open position, the inlet valve40allows or opens fluid communication between the first inlet28of the first tank24and the fluid coupler36to allow fluid flow between the first tank24and the fluid coupler36. When disposed in the closed position, the inlet valve40does not allow or closes fluid communication between the first inlet28of the first tank24and the fluid coupler36, to prevent fluid flow between the first tank24and the fluid coupler36. The inlet valve40may include any style and/or configuration of valve capable of moving between the open position and the closed position described above, as long as such valve provides fluid isolation (both gas and liquid) of the testing device internal passages from outside atmospheric conditions. In other words, the inlet valve40must not leak externally at the pressures used in the test process. For example, the inlet valve40may include, but is not limited to, a ball valve, a gate valve, or some other similar control valve. The inlet valve40may be manually operated between the open position and the closed position, or may be controlled by an electronic, computer controller.

The second inlet32of the second tank26is disposed in fluid communication with the first outlet30of the first tank24. The first outlet30of the first tank24is disposed vertically above the second inlet32of the second tank26. Accordingly, the first outlet30of the first tank24is disposed at a higher relative elevation than the second inlet32of the second tank26.

A transfer valve42interconnects the first outlet30of the first tank24and the second inlet32of the second tank26, to control fluid flow between the first tank24and the second tank26. The transfer valve42is operable or controllable between an open position and a closed position. When disposed in the open position, the transfer valve42allows or opens fluid communication between the first outlet30of the first tank24and the second inlet32of the second tank26to allow fluid flow between the first tank24and the second tank26. When disposed in the closed position, the transfer valve42does not allow or closes fluid communication between the first outlet30of the first tank24and the second inlet32of the second tank26, to prevent fluid flow between the first tank24and the second tank26. The transfer valve42may include any style and/or configuration of valve capable of moving between the open position and the closed position described above. For example, the transfer valve42may include, but is not limited to, a ball valve, a gate valve, or some other similar control valve. The transfer valve42may be manually operated between the open position and the closed position, or may be controlled by an electronic, computer controller.

A drain valve44is attached to the second outlet34of the second tank26for controlling fluid flow through the second outlet34. The drain valve44is operable or controllable between an open position and a closed position. When disposed in the open position, the drain valve44allows or opens fluid communication between the second outlet34of the second tank26and atmosphere to drain fluid from the second tank26. When disposed in the closed position, the drain valve44does not allow or closes fluid communication between the second outlet34of the second tank26and the outside atmosphere, to prevent fluid from draining from the tank. The drain valve44may include any style and/or configuration of valve capable of moving between the open position and the closed position described above. For example, the drain valve44may include, but is not limited to, a ball valve, a gate valve, or some other similar control valve. The drain valve44may be manually operated between the open position and the closed position, or may be controlled by an electronic, computer controller.

The second tank26includes an absolute pressure sensor46. The absolute pressure sensor46is operable to sense an absolute pressure within the second tank26. Preferably, the absolute pressure sensor46includes a digital sensor, and be coupled to and in communication with a computer or other similar electronic controller. However, it should be appreciated that the absolute pressure sensor46is not required to include a digital sensor. The absolute pressure sensor46measures pressure relative to a perfect vacuum. A “perfect vacuum” is defined herein as a volume or region containing no matter. Because all pressure readings from the absolute pressure sensor46are relative to a perfect vacuum, all pressure readings are always a positive number. The fluid testing device20uses the absolute pressure sensor46to prevent fluctuations in pressure measurement caused by variation in atmospheric pressure.

As shown in the Figures, the absolute pressure sensor46is directly attached to the second tank26via a dedicated port. The fluid testing device20may further includes a baffle48disposed within an interior50of the second tank26. The baffle48is positioned to shield a probe or tip of the absolute pressure sensor46that may extend into the interior50of the second tank26. The baffle48may be configured in any manner capable of shielding probe of the absolute pressure sensor46, while still allowing the absolute pressure sensor46to sense the absolute pressure within the second tank26. Alternatively, the absolute pressure sensor46may be attached to the second tank through one or more pipe fittings interconnecting the transfer valve42and the second inlet32of the second tank26. Such a configuration may include a protective valve disposed between the second inlet32and the absolute pressure sensor46to protect the absolute pressure sensor from high fluid pressures during fluid transfer between the first tank24and the second tank26.

The first tank24defines a first volume52, and the second tank26defines a second volume54. The second volume54of the second tank26is larger than the first volume52of the first tank24. The reason and importance of having the second tank26larger than the first tank24is described in greater detail below. In an exemplary embodiment, the second volume54may be between 2% and 50% larger than the first volume52, and more specifically, the second volume54may be between 5% and 15% larger than the first volume52. The first volume52and the second volume54may each include a volume between 200 cc and 3000 cc. However, it should be appreciated that the relative size between the first volume52and the second volume54, as well as the absolute sizes of the first volume52and the second volume54, may differ from the exemplary sizes and ranges provided herein.

A method of testing a pressurized fluid22for dissolved and/or entrained gasses, with the fluid testing, is described below. As noted above, an exemplary use for the fluid testing device20and method described herein may include testing brake fluid from an evacuation and brake fluid filling system used to fill a hydraulic brake system of vehicles being manufactured in an automotive assembly plant. However, it should be appreciated that the test procedure may be used for other fluids intended for other applications.

As shown in the Figures, a closed valve is indicated by a solid or filled valve symbol, whereas an open valve is indicated by non-solid or non-filled valve symbol. The fluid being tested is generally indicate by the stippling pattern, and identified by reference numeral22.

Referring toFIG. 1, the test procedure begins with the fluid testing device20disposed in a storage position, shown inFIG. 1, in which the inlet valve40and the drain valve44are disposed in their respective closed positions, and the transfer valve42is disposed in its respective open position. This storage position allows residual fluid from the previous test to drain from the first tank24into the second tank26(and subsequently be drained out of the drain valve44prior to beginning the next test) and also to prevent continuous exposure of the internals of the fluid testing device20to the atmosphere which would potentially allow atmospheric moisture to be absorbed by the residual fluid in the fluid testing device20(the test fluid potentially being hydrophilic, such as brake fluid). Moisture inside of the fluid testing device20may interfere with test results and is not desired. Any moisture inside of the fluid testing device should be purged as part of the test process. Keeping the fluid testing device20in the storage position limits atmospheric moisture from collecting within the fluid testing device20, thereby reducing the time required to purge any moisture in the fluid testing device20prior to the next test process.

Referring toFIG. 2, prior to beginning the test proper, a preparatory step is required. Assuming the fluid testing device is stored in the storage position, in which the inlet valve40and the drain valve44are closed, and the transfer valve42is open, then the preparatory step includes briefly opening the inlet valve40and the drain valve44to allow any residual fluid to drain out of the fluid testing device20. The drain valve44is maintained open until any residual fluid stops dripping from the second outlet34of the second tank26. Once any residual fluid has drained out of the fluid testing device20, the fluid testing device20is re-positioned into an initial test position, shown inFIG. 3in which the inlet valve40and the transfer valve42are disposed in their respective open positions, and the drain valve is disposed in its respective closed position.

Referring toFIG. 3, the start of the test proper includes connecting the evacuation and fluid filling system38to the first tank24. As noted above, the evacuation and fluid filling system38is capable of forming a vacuum in a closed system/container, and also introducing or supplying a fluid under pressure to the closed system after the vacuum has been formed. Connecting the evacuation and fluid filling system38to the first tank24includes attaching or coupling the evacuation and fluid filling system38to the fluid testing device20with the fluid coupler36, as described above.

After connection of the evacuation and fluid filling system38to the fluid coupler36, the evacuation and fluid filling system38may be engaged to evacuate both the first tank24and the second tank26to form a vacuum in both the first tank24and the second tank26. For example, a vacuum pump56of the evacuation and fluid filling system38may be actuated to pump air from the first tank24and the second tank26to form a vacuum therein. The removal of air from the fluid testing device20is generally shown by the flow arrow60. It should be appreciated that because the transfer valve42begins the test procedure in its respective open position, the first tank24and the second tank26are in fluid communication with each other. As such, as the vacuum pump56draws air from the first tank24, the vacuum pump56is simultaneously drawing air from the second tank26to form a vacuum in each of the first tank24and the second tank26.

After evacuating the first tank24and the second tank26, and a vacuum has been formed in the first tank24and the second tank26, the vacuum in both the first tank24and the second tank26may be maintained for a pre-defined vacuum soak period to remove moisture and/or any dissolved gasses from the residual fluid in the fluid testing device20which may interfere with the test results if not removed prior to the test. The process shall be hereafter referred to as “pre-test outgassing”. The pre-defined vacuum soak period may be between 5 and 30 minutes, or as needed until the pre-test outgassing process is complete. After the pre-determined soak time, during which the vacuum pump56of the fluid evacuation and filling system38is providing the vacuum, fluid communication between the evacuation and fluid filling system38and the first tank24is closed by moving the inlet valve40into its respective closed position, such as shown inFIG. 4A.

Referring toFIG. 4B, once the first tank24and the second tank26have been drawn down to a deep vacuum, and fluid communication between the evacuation and fluid filling system38has been closed, the fluid evacuation and filling system38is disconnected from the fluid testing device20for a pre-defined vacuum soak period, to test for leakage through either the inlet valve40or the drain valve44. The pre-defined vacuum soak period may include any desirable period of time suitable for testing for leaks in the fluid testing device20. For example, the pre-defined soak period may include a time of between 5 minutes and 30 minutes. It should be appreciated that a longer vacuum soak period will provide a more accurate test of the ability of the fluid testing device20to maintain the vacuum and assurance of proper outgassing.

While the fluid testing device20is isolated from the fluid evacuation and filling system38, with the first tank24and the second tank26at a deep vacuum, the absolute pressure sensor46is monitored in order to test for sufficient outgassing of the residual fluid and to assure there are no leaks in the fluid testing device20. If the pressure level in the first tank24and the second tank26, as measured by the pressure sensor46, is shown to rise at this point, additional outgassing time may be needed to more completely remove any moisture and/or dissolved gasses in the residual fluid in the fluid testing device20, or leaks in the fluid testing device20may need to be found and repaired prior to proceeding with the test procedure. This test for a rise in pressure shall be subsequently referred to as the “vacuum decay check”. Additional outgassing, if needed, is provided by once again connecting the fluid evacuation and filling system30to the fluid testing device20, engaging the vacuum pump56, and opening the inlet valve40for some period of time.

If the absolute pressure reading from the fluid testing device20does not change significantly during the vacuum decay check, then the fluid testing device20remains sealed, and the test process may be continued. However, if the absolute pressure reading from the fluid testing device20does change during the vacuum decay check, then the fluid testing device20is not operating properly, and the test procedure should be stopped. If there is no significant loss of the deep vacuum in the fluid testing device20, the pre-test vacuum decay check is considered passed and the process continues. A significant loss of the deep vacuum is indicated by a pressure increase greater than 0.1 torr per second.

Referring toFIG. 4C, after the vacuum in the first tank24and the second tank26has been maintained for the pre-defined vacuum soak period, and assuming the fluid testing device20has maintained the vacuum within the first tank24and the second tank26, and the fluid testing device20is deemed to be operating properly, then the fluid evacuation and filling system38is re-connected to the fluid testing device20, and a vacuum is re-applied to the fluid testing device20to bring both the first tank24and the second tank26back down to as deep of a vacuum level as possible in case there was any minor loss of vacuum inside the fluid testing device20during the vacuum decay check. The re-application of vacuum also clears the air from the interface between the evacuation and filling system38and the fluid coupler36to avoid air exposure to the fluid22when it is provided to the fluid testing device20later in the test process via this same pathway.

Referring toFIG. 4D, once the first tank24and the second tank26have been brought down to the deepest possible vacuum by the vacuum pump56, then fluid communication between the first tank24and the second tank26is closed. Fluid communication between the first tank24and the second tank26is closed by moving the transfer valve42into its respective closed position, thereby preventing fluid communication between the first tank24and the second tank26.

Referring toFIG. 5A, after fluid communication between the first tank24and the second tank26is closed, fluid communication between the first tank24and the evacuation and fluid filling system38is opened to enable introduction of a test volume of the pressurized fluid22into the first tank24. A portion of the supply volume of the pressurized fluid22is introduced into the first tank24through the evacuation and fluid filling system38. The volume of the pressurized fluid22to be tested, hereinafter referred to as “the test volume”, is approximately equal to the first volume52of the first tank24, as the first tank24will be completely filled and pressurized until flow into the first tank24stops due to equalized pressure (the supply volume pressure becomes the same as the test volume pressure). The test volume of the pressurized fluid22may be introduced into the first tank24at a pressure between 30 psi and 150 psi, and at approximately any normal indoor ambient temperature suitable for production workers.

Referring toFIG. 5B, once the test volume of the pressurized fluid22is introduced into the first tank24, fluid communication between the first tank24and the evacuation and fluid filling system38is closed, and the evacuation and fluid filling system38is disconnected from the first tank24. Fluid communication between the first tank24and the evacuation and fluid filling system38is closed by moving the inlet valve40into its respective closed position. The evacuation and fluid filling system38is disconnected from the fluid testing device20by disengaging the fluid coupler36.

After fluid communication between the first tank24and the evacuation and fluid filling system38has been closed, an initial absolute pressure in the second tank26is sensed with the absolute pressure sensor46. The initial absolute pressure reading may be taken manually by an operator viewing the absolute pressure reading, or may be communicated to an electronic controller via an electric signal. The initial absolute pressure may be recorded, or saved in memory of an electronic controller for later use.

Referring toFIG. 6, after the initial absolute pressure is sensed with the absolute pressure sensor46, fluid communication between the first tank24and the second tank26is opened to allow the test volume of the pressurized fluid22to flow from the first tank24into the second tank26. Fluid communication between the first tank24and the second tank26is opened by moving the transfer valve42into its respective open position. As noted above, the first tank24is disposed vertically above the second tank26so that the test volume of the pressurized fluid22may flow by gravity from the first tank24into the second tank26. Furthermore, because the transfer valve42was closed after forming the vacuum in both the first tank24and the second tank26, and prior to introduction of the pressurized fluid22into the first tank24, a vacuum exists in the second tank26.

After the transfer valve42is opened to allow the pressurized fluid22to flow from the first tank24into the second tank26, the fluid22de-pressurizes, and the test volume of the previously pressurized fluid22is maintained in the second tank26for a pre-defined out-gassing period, to allow any moisture and dissolved or entrained gasses in the test volume of the previously pressurized fluid22to separate from the liquid portion of the fluid22and to be measured by the change in reading of the absolute pressure sensor46at the end of the test process.

When the pressurized fluid22is introduced into the first tank24, it is initially at a pressure that is significantly higher than the vacuum pressure in the second tank26. At the higher pressure conditions (temperature assumed to be relatively constant throughout the test process), the liquid had allowed a solubility of a certain amount of air in that physical state. Air content beyond this level, if any, would not have been able to become dissolved and would have remained entrained in the liquid while under pressure. When the transfer valve42is opened the pressure of the first volume52of the fluid22in the first tank24, being almost completely incompressible with exception of the minor amount of entrained air, if any, will almost instantly drop to the approximate vacuum level previously existing in the lower tank26(a near perfect vacuum). The level of this equalized pressure (both tank volumes and all matter within now being at one common absolute pressure) will almost immediately be an indication of the amount of entrained air that was in the liquid, which being less dense, will now have expanded into the void over the liquid level impacting the equalized pressure. Over the subsequent out-gassing time period, the dissolved air will now slowly come out of solution as well, with the assumption that a near perfect vacuum remains and was not significantly degraded by unusual quantities of entrained air. Note that the pressurized fluid22, being properly processed initially, should have virtually no entrained air and that the vacuum level therefore should remain deep enough to cause the dissolved air outgassing of the liquid to proceed unabated. Note also that if enough air is entrained in the pressurized fluid22as delivered to the testing device20(a very large and unexpected amount), that the vacuum level resulting after equalization may be high enough to interfere with the complete removal of the dissolved gas in the liquid. In this case, the testing device20will still convey useful information that indicates this poor quality of processed fluid22and the need to address the issue prior to pursuing a more accurate and subsequent “dissolved air only” test should such a test be desired. Also, note that any indication of the existence of entrained air (by abnormally high equalization pressure for example), is also an indication that the level of dissolved air was at the saturation level for the physical conditions that existed when the pressurized fluid sample22was introduced into the testing device20. The reason is that if any room for additional dissolved air had existed at those conditions, the entrained air would have dissolved into solution given some exposure time with the fluid at those conditions. So any evidence of entrained air measured is also an indication that the dissolved air level of the sample was saturated. All said then, the existence of entrained air does not invalidate the testing device20as a dissolved air detector and a distinction between the level of dissolved vs entrained gas present in the pressurized fluid test sample22is not critical to differentiate in order to derive meaning from the test results.

It is important to note that despite the difference in size of the first tank24as compared to the second tank26, that the volume of physical space in the testing device20, which is void of liquid prior to the transfer of the pressurized fluid from the first tank24into the second tank26remains the same as after the transfer (it is approximately equivalent to the volume of the first tank26in both cases). This being true, and considering the perfect gas law, the transfer itself will have no impact on the pressure of the fluid due to a change in volume which constrains any gas that may exist, or at some point come out of solution, internal to the test tool. Thus any change in measurable pressure is strictly due to the release of dissolved gas (entrained gas being absent as intended) from the liquid portion of the test sample. The reasoning for the second tank26being slightly larger than the first tank24is to allow some space which will be assured to be void of liquid fluid so that the absolute pressure sensor46, being designed to measure the pressure of a gas volume, will not be submerged in liquid which may interfere with its ability to make a proper measurement. It should also be noted, again considering the perfect gas law, that the sensitivity of a pressure measurement, as impacted by the quantity of gas being removed from the liquid, will be directly impacted by the size of the space allowed for gas to accumulate. The size of this space is, in turn, determined by the relative difference in size between the two tanks. So a smaller difference in relative tank size will give more sensitivity/resolution of a pressure measurement. As a result, the first tank25and the second tank26should not be excessively different in size but only enough to assure proper operation of the absolute pressure sensor46.

Another concept impacting measurability of the results is the absolute size of the two tanks24,26. If both tanks were to be larger, or both were smaller, for example, it would impact the amount of pressurized fluid22that could be tested, and as a result, the amount of dissolved gas that may potentially be produced by the test process. Thus a larger sample size may produce more gas which may produce a larger, more measurable difference in pressure as seen by the absolute pressure sensor46. All said and done, once optimal absolute and relative tank sizes are determined, either empirically or in theory, it is critical to compare results from test to test with those sizes constant in order to get meaningful comparative test results with respect to the amount of dissolved air that existed in the pressurized fluid sample22presented for analysis.

Referring toFIG. 7A, the de-pressurized fluid22is maintained in the second tank26for a pre-defined out-gassing period, to ensure that all dissolved gas has separated from the de-pressurized fluid22. The pre-defined out-gassing period may include any time period required for the specific fluid being tested. For example, the pre-defined out-gassing period may be in the range of between 5 minutes and 20 minutes. However, the pre-defined out-gassing period may vary from the exemplary range provided herein.

Referring toFIG. 7B, after the test volume of the pressurized fluid22has been maintained in the second tank26for the pre-defined out-gassing period, and the released gasses have collected at the top of the second tank26, a final absolute pressure is sensed in the second tank26with the absolute pressure sensor46. As noted above, a change in the absolute pressure in the second tank26is related to the separation of gasses and moisture from the pressurized fluid22. A difference between the final absolute pressure and the initial absolute pressure may be calculated by subtracting the initial absolute pressure from the final absolute pressure. The difference between the final absolute pressure and the initial absolute pressure may then be correlated to a volume or quantity of gasses released from the test volume of the pressurized fluid22. It should be noted that the pressurized fluid sample22may be so well processed prior to testing (extremely low or devoid of dissolved air) as to be called “super-processed” by some skilled in the art. A super-processed sample may actually lower the absolute pressure level in the second tank26when introduced to that tank because that pressure level may not be at zero absolute pressure initially (perfect evacuation is not actually feasible with the equipment used in automotive manufacturing, although the level gets very near perfect). So some amount of the residual air in the second tank26, which remains prior to introduction of the fluid sample, can then be absorbed into solution (dissolved) by the super-processed fluid (the super-processed fluid not being saturated even at the very low pressure state that exists at this point) if such a well processed fluid is introduced. Thus the decay (final minus initial absolute pressure) may be negative thus indicating excellent super-processed fluid quality of the introduced sample. Note that a negative decay is not the same as a negative absolute pressure which is not physically possible, yet an end reading with a perfect vacuum (0.0 mmHg) can actually be achieved via this test method, and in theory, in a vehicle brake system. Any portion of the gasses released from the pressurized fluid22related to moisture in the fluid may be empirically correlated to an expected pressure change, based upon the boiling point of the fluid sample that was predetermined by independent known test methods applied to another sample from the same equipment which is being tested. Any increase in pressure over and above this value is attributed to dissolved gasses in the test sample.

Once the test is complete, and the change in pressure has been correlated to the volume of gasses in the test volume of the pressurized fluid22, the drain valve44and the inlet valve40may be moved to their respective open positions, such as shown inFIG. 8, to allow fluid flow through the second outlet34of the second tank26, in order to drain the test volume of the fluid22from the second tank26. Some non-critical drain time may be allowed for draining the majority of the sample from the fluid testing device20, although some residual fluid22may remain, and no rinsing of the fluid testing device20with a solvent is required. After the draining period, the fluid testing device20is returned to the storage position shown inFIG. 1, and described above.

The test results from the procedure described above, i.e., the volume or quantity of gas that was released from the test volume of the pressurized fluid22(as determined by the change in absolute pressure over the test period), may be tracked over time and/or used for several different purposes. For example, the test may be performed as a quality control to ensure that the fluid is being properly processed to remove the requisite amount of gas and/or moisture prior to installation into the hydraulic system. By tracking the test results over time, a malfunction in the processing or pressurized transport of the fluid may be detected. Furthermore, the test procedure may be used to compare different fluid processing techniques, to determine which technique is the most efficient at removing moisture and gasses from the fluid, and/or which is more cost effective. Alternatively, a malfunction in the evacuation performance of the evacuation and fluid filling system38may also be detected. For example, with minor modifications of the test process, the performance of the vacuum pump56of the evacuation and fluid filling system38may be tested.

A test of the evacuation performance of the evacuation and fluid filling system38would still require the pre-test outgassing step (including extended vacuum soak time for both tanks) in order to assure that moisture in the residual fluid in the fluid testing device20(from previous testing) would not influence the subsequent test results and also to assure that there is no leak in the fluid testing device20or leak in the interface between the evacuation and filling system38and the fluid testing device20. For this testing of the evacuation performance of the fluid evacuation and filling system38, after the pre-test outgassing, vacuum soak period and passing of the vacuum decay check, the first tank24would briefly be returned to atmospheric pressure, instead of proceeding directly to filling the first tank24without releasing the vacuum as described above. The second tank26would remain isolated form the first tank24and would remain under deep vacuum from the pre-test soak. At this point, the evacuation and filling test procedure described above may be performed using only the manufacturing production process vacuum evacuation period (in this case for the first tank only), thus testing the evacuation pumping capability to remove air to a very low absolute pressure very quickly as need in the manufacturing production environment.

Such a time period for the removal of air in the manufacturing environment may, for example, be in the range of 45 and 100 seconds. This manufacturing process is normally applied to a vehicle brake system that is expected to be very dry (no vacuum soak period should be needed, unlike the test fixture), as well as leak free via previous positive pressure leak checking of the system. As a result, the test fixture is both vacuum soaked and leak checked to simulate the condition of the vehicle system but then returned to atmospheric pressure conditions to enable testing of the ability of the evacuation and fill machine vacuum pump56, to remove air efficiently and effectively in a limited amount of time (indicating normal operational capability). Any amount of air not fully removed in the allotted time will show up in the final test results, the same way that the dissolved gas test would show results, but in this case would primarily be an indication of vacuum pump performance.