Volatility testing by Reid method: In the Reid vapor pressure (RVP) apparatus for petrofuels at 100°F, what is the ratio of the air (vapor) chamber volume to the liquid fuel chamber volume?
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A1
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B2
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C3
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D4
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E5
Answer
Correct Answer: 4
Explanation
Introduction / Context: Reid vapor pressure (RVP) is a legacy yet widely referenced measure of fuel volatility. The test uses a sealed apparatus with a defined vapor-to-liquid volume ratio to standardize the partial pressure measured at 100°F (approximately 37.8°C).
Given Data / Assumptions:
- Standard RVP test temperature: 100°F.
- Measurement in a closed volume with specified vapor and liquid chambers.
- Fuel equilibrated with its own vapor plus small air space.
Concept / Approach: The Reid method specifies a vapor-to-liquid chamber volume ratio of 4:1. This ensures reproducible vaporization and pressure reading across labs and fuels.
Step-by-Step Solution:
1) Identify the apparatus design: separate air (vapor) chamber and liquid chamber.2) Apply the standard: vapor space volume is four times the liquid chamber volume.3) Read the gauge pressure as the Reid vapor pressure at equilibrium.Verification / Alternative check: ASTM procedure descriptions and refinery handbooks state the 4:1 vapor-to-liquid volume ratio for the Reid bomb.
Why Other Options Are Wrong:
(a)–(c) Ratios 1, 2, or 3 do not match the Reid standard.(e) A 5:1 ratio is not used in the canonical Reid method.Common Pitfalls: Confusing Reid vapor pressure (legacy) with true vapor pressure (TVP); the apparatus ratio is specific to the Reid method.
Final Answer: 4