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D4953-20 – Standard Test Method Technical Guide
📐 Scope and Applicability
ASTM D4953-20 specifically addresses the measurement of vapor pressure for gasolines and gasoline-oxygenate blends using a dry method modification of the standard Reid procedure (D323). This test method is applicable to samples with a vapor pressure range of 35 kPa to 100 kPa (5 psi to 15 psi) at the prescribed test temperature of 37.8 °C (100 °F). The standard provides two distinct procedures for determination.
💡 Important Distinction: Unlike the traditional Reid method, D4953 is a “dry method” which minimizes water contamination by modifying the air saturation process. The measured vapor pressure is absolute, as the atmospheric pressure initially present in the air chamber is counteracted during the test.
While materials with vapor pressures outside the primary range can be tested, the precision and bias statements defined in Section 11 are not applicable. For samples exceeding 100 kPa (15 psi), a dedicated 0 kPa to 200 kPa (0 to 30 psi) gauge is mandatory, as specified in the annex of Test Method D323. SI units govern the standard values, with imperial units provided in parentheses for reference.
📊 Key Specifications and Apparatus
The accuracy of D4953-20 relies on the correct selection and use of the apparatus, particularly the pressure gauge, which utilizes a Bourdon spring mechanism. This sensor features a flattened metal tube bent to a curve that straightens under internal vapor pressure. The following table summarizes the core technical specifications defined within the standard.
| 🟦 Parameter | 📏 Standard Value / Spec | 🎯 Critical Notes |
|---|---|---|
| Test Temperature | 37.8 °C (100 °F) | Absolute temperature for vapor-liquid equilibrium. |
| Primary VP Range | 35 kPa to 100 kPa (5 to 15 psi) | Scope where precision data is valid. |
| Extended VP Gauge | 0 to 200 kPa (0 to 30 psi) | Mandated for materials > 100 kPa. |
| Air Saturation Temp. | 0 °C to 1 °C | Haze observed here must be reported. |
| Gauge Element | Bourdon Tube | Standard pressure measurement sensor. |
⚠️ Handling Hazy Samples: Per Section 9.4, if a sample appears hazy after cooling to 0 °C to 1 °C, this observation must be explicitly noted in the reporting of results. The user should be aware that precision and bias statements for hazy samples have not yet been determined (Note 7).
❓ Frequently Asked Questions
🔍 What is the specific test temperature for ASTM D4953-20?
The standard specifies a test temperature of 37.8 °C (100 °F) for the vapor-liquid equilibrium measurement.
💡 How does the “Dry Method” differ from the standard Reid Method (D323)?
D4953-20 is a modification of D323 designed to minimize water contamination of the sample. It eliminates the water bath typically used for the initial air saturation of the sample, replacing it with a dry cooling procedure.
⚡ What should I do if my sample’s vapor pressure exceeds 100 kPa (15 psi)?
According to Section 1.1, if the vapor pressure is greater than 100 kPa, the precision and bias of this method do not apply. You must use a 0 kPa to 200 kPa (0 to 30 psi) gauge as specified in the annex of Test Method D323.
📌 What constitutes the primary vapor pressure measurement device in this standard?
The standard specifies the use of a Bourdon spring gauge, which utilizes a bourdon tube—a flattened metal tube bent to a curve that straightens under internal pressure—to indicate the vapor pressure.