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D5190-07 – Standard Test Method Technical Guide
📐 Scope and Definitions
This test method covers the determination of the total vapor pressure of air-containing, volatile petroleum products with boiling points above 0°C (32°F). It is specified for samples exerting a vapor pressure between 7 and 172 kPa (1 and 25 psi) at 37.8°C (100°F) at a vapor-to-liquid ratio of 4:1. The method is suitable for gasoline samples containing oxygenates, such as alcohols or ethers, but does not account for dissolved water. Haze observed in samples at 0 to 1°C must be reported, as precision for such samples is not determined.
| 🟦 Parameter | 📏 Specification |
|---|---|
| Test Temperature | 37.8°C (100°F) |
| Vapor Pressure Range | 7 to 172 kPa (1 to 25 psi) |
| Vapor-to-Liquid Ratio | 4:1 |
| Minimum Boiling Point | 0°C (32°F) |
Key terminology is defined in Section 3 of the standard. Total vapor pressure is the observed pressure measured in the experiment, including partial pressure of sample and dissolved air. Dry vapor pressure equivalent (DVPE) is a calculated value expected to be comparable to results from Test Method D4953. Gasoline-oxygenate blend refers to spark-ignition engine fuel primarily consisting of gasoline with one or more oxygenates.
⚙️ Test Procedure and Equipment
The automatic vapor pressure instrument is utilized with a chilled sample cup filled with chilled sample. The cup is coupled to the instrument inlet fitting, and the sample is automatically forced from the sample chamber to the expansion chamber. It is then held until thermal equilibrium at 37.8°C (100°F) is reached, during which the sample expands to five times its volume (4:1 vapor-to-liquid ratio). The vapor pressure is measured by a pressure transducer, and the instrument automatically converts this measurement to a DVPE value, applying a correction for bias against Test Method D4953.
⚠️ Important Note: Some gasoline-oxygenate blends may exhibit a haze when cooled to 0 to 1°C. If haze is observed, it must be indicated in the reporting of results, as precision and bias for hazy samples have not been determined per Note 8 of the standard.
The method includes automatic calculation of DVPE, which is essential for alignment with the dry vapor pressure method.
📊 Key Measured Properties and Calculations
The primary measured property is the total vapor pressure at 37.8°C. From this, the Dry Vapor Pressure Equivalent (DVPE) is calculated using a defined correlation equation as specified in Section 13.1. The DVPE closely approximates the dry vapor pressure that would be obtained on the same material when tested in accordance with Test Method D4953. The values stated in SI units are regarded as the standard.
| 📐 Term | 🎯 Definition |
|---|---|
| Total Vapor Pressure | Sum of the partial pressure of the sample and the partial pressure of the dissolved air. |
| Dry Vapor Pressure Equivalent (DVPE) | Value calculated by a defined correlation equation, comparable to Test Method D4953. |
| Vapor Pressure | Pressure exerted by the vapor of a liquid when in equilibrium with the liquid. |
💡 Technical Tip: The DVPE correction is automatically applied by the instrument to account for observed bias between the test result and that obtained by Test Method D4953. Ensure the correlation equation is up-to-date for accurate results.
❓ Frequently Asked Questions
🔍 What is the standard test temperature for this method?
The test is conducted at 37.8°C (100°F) after thermal equilibrium is reached in the expansion chamber.
💡 How is the Dry Vapor Pressure Equivalent (DVPE) calculated?
DVPE is calculated from the measured total vapor pressure using a defined correlation equation, and the instrument applies a correction for bias against Test Method D4953.
⚡ What vapor-to-liquid ratio is used in this test method?
The ratio is 4:1, meaning the sample expands to five times its volume during the test.
📌 Why must hazy samples be reported specifically?
Precision and bias for samples showing haze have not been determined, so their presence must be noted in results to ensure accurate interpretation.