| Objective: | Develop a sensor to measure the amounts of free and dissolved air in the hydraulic fluid
| Description: | Excessive air in hydraulic fluid can cause severe problems in aircraft hydraulic systems. Not only does excess air cause poor response from the system to inputs from the pilot, but it also reduces the stiffness of the control surfaces. An additional problem caused by excess air is cavitation that occurs when the air comes out of the fluid resulting in severe damage to the components as well as localized degradation of the hydraulic fluid. These problems are manifested when there is free air in the hydraulic fluid. At normal temperature and pressure, approximately 18 percent of air by volume is soluble in the military hydraulic fluids, (MIL-PRF-83282, MIL-PRF-87257 and MIL-PRF-5606). In order to prevent free air from forming in the fluid, the sensor must be capable of measuring both the free air and the dissolved air in the hydraulic fluid. The sensor must be compatible with the hydraulic fluids and functional over the anticipated temperature range of the hydraulic fluid of -40 to 275 degrees F. The sensor is not to be mounted on aircraft but on ground support equipment, e.g., hydraulic fluid purifier or hydraulic test stand.
| | PHASE I: Demonstrate the feasibility of the technical approach proposed to measure the dissolved and free air content of military aerospace hydraulic fluids over the temperature range of -40 to 275 degrees F.
| | | PHASE II: The Phase II effort will build on the technology demonstrated during the Phase I contract and will develop it into a working prototype. The long term compatibility of the sensor with MIL-PRF-87257, MIL-PRF-83282 and MIL-PRF-5606 will be demonstrated. Calibration procedures will be developed that will be simple enough to use in the field.
| | DUAL USE COMMERCIALIZATION: If necessary, modification may be needed to make it compatible with commercial aerospace hydraulic fluids, such as Skydrol and Hy-Jet hydraulic fluids, which are phosphate ester based rather than hydrocarbon based like the military aerospace hydraulic fluids. Additionally, the sensor could also be modified for use in other fluids where the air content requires to be measured.
| References: | Military Aerospace Fluids and Lubricant Workshop Proceedings, November 2004.
| | Keywords: | hydraulic fluid, sensors, air sensors, hydraulic fluid purification
|
Questions and Answers: |
Q: Q.1) What is the anticipated pressure range in the hydraulic fluid that the sensor needs to be functional in?
Q.2) What is the maximum amount of Air that needs to be detected in the temperature (-40 to 275C) and in the max pressure ranges?
Q.3) What are the specific articles of relevance in the reference "Military Aerospace Fluids and Lubricant Workshop Proceedings 2004"? |
A: 1. From ambient pressure to 100 psi
max.
2. The range of
greatest importance is from 12% down to 4% which should,under most
circumstances all be dissolved air. While we do want to know if there is
free air in the hydraulic fluid, the actual amount is of lesser importance.
3. There are two
presentations on sensor technology for hydraulic fluid/systems. The one
most relevant discusses a hydraulic fluid multi-contamination sensor which
will measure the amount of particulate contamination and water in hydraulic
fluid, real time.
|
Q: Is there a current invasive method that is used to detect dissoled air? |
A: Currently there is no field-level method used to detect dissolved air. The
only procedure that has been used successfully by our laboratory is an ASTM
gas chromatographic method that is not suitable for field use. That is the
reason we are sponsoring this SBIR topic. |
Q: With regards to sample time, is 30 to 60 minutes reasonable to ascertain the amount of free air and dissolved air in the fluid? |
A: No, since it is anticipated that we will be working with a hydraulic fluid
whose contaminant level will be changing as a result of purification, a 30
to 60 analysis time would not provide relevant data to the state of the
fluid. The analysis time should be no greater than approximately 10
seconds. |
Q: 1) If results are supplied in 10-20 seconds, what accuracy is required (eg +/*-20%)?
2) Is the accuracy on total gases or on each individual gas (eg oxygen, nitrogen, CO2)?
3) Are there any limitations on circulating the oil? Can I circulate at 3-10 gallons per minute? |
A: 1. The accuracy of the air content should be +/- 10% of
the value. For example, it should be 8% +/- 1%.
2. We are only interested in total gases and that should be air
which is composed of ~80% nitrogen and ~20% oxygen.
3. The oil will already be circulated for you and the
rate can vary, but will probably be fixed at a relatively low flow rate for
the particulate and water contamination sensors that will be part of this
suite of hydraulic fluid contamination sensors. The specific rate of the
anticipated flow could be requested from Dr. Ken Heater of METSS Corp. who
is developing the other two sensors. The phone number is (614)797-2200.
|
Q: What is the definiation of the fee and dissolved air in the hydraluic fluids?
Are small air bubles the fluids with a diameter about 10-50 micronmeters free or dissolved?
|
A: Free air is that which is present in excess of the
maximum soluble under the prevailing conditions of temperature and pressure.
Under standard temperature and pressure, the appoximate solubility for air
is 12%. Any air in excess of that present in the fluid will be in the form
of free air or bubbles. Dissolved air is not observable in the fluid like
any other dissolved components.
|
Q: Can you provide an estimate of the electrical conductivity of the military hydraulic fluids? |
A: No, not really because not only do the compositions of the various qualified
oils to the specifications vary since they are not composition
specifications, but performance specifications. Another factor is that they
oils will pick up water during use which would change the electrical
conductivity of the fluids. |