Overview
EN ISO 13758:1996 - Liquefied petroleum gases - Assessment of the dryness of propane - Valve freeze method describes a standardized, functional test for moisture in LPG (propane/propene) using the valve freeze method. Prepared by ISO TC 28 and adopted by CEN, this procedure determines whether LPG is sufficiently dry to avoid freezing-related malfunctions in pressure‑reducing regulators used in domestic, industrial and automotive applications.
Keywords: EN ISO 13758:1996, propane dryness, LPG testing, valve freeze method, freeze-off time, pressure‑reducing systems.
Key topics and requirements
- Test principle: A liquid-phase aliquot flows through a calibrated test valve; vaporization cools the valve and subsequent closure to a preset orifice allows observation of the freeze-off time (time until flow stops).
- Pass/fail use: Typically applied as a functional pass/fail test (common criterion: pass if freeze-off time > 60 s, fail if ≤ 60 s).
- Apparatus:
- Precision LPG test valve with a wide‑open purge position and a small pre‑set orifice.
- Stopwatch accurate to at least 0.2 s.
- Pressurized sample container (minimum 11.5 L) if not testing at the bulk source.
- Clean, dry cloth for wiping.
- Sampling and test location: Moisture measurements are highly sensitive to sampling error - the standard recommends testing at the LPG supply source where possible. If sampling is required, sample according to ISO 4257 (method of sampling).
- Procedure essentials:
- Purge and cool the valve in the wide‑open position, then switch to the test orifice and start timing.
- Disregard the first run; repeat until three consecutive freeze‑off times are within ±2 s.
- If three consecutive runs exceed 180 s, report as “over 180 s”.
- Reporting: Report average of three valid runs to the nearest second; include deviations, product ID and test date.
- Safety note: The standard warns about hazardous materials and operations - users must follow appropriate health and safety practices.
Practical applications and users
Who uses EN ISO 13758:1996:
- LPG producers and bottlers for quality control and batch acceptance.
- Distributors and transporters validating product dryness before delivery.
- Gas appliance and regulator manufacturers assessing susceptibility to freeze blockage.
- Test laboratories and regulatory bodies performing compliance and safety checks.
- Maintenance teams troubleshooting intermittent regulator failures suspected to be moisture-related.
Practical benefits:
- Prevents regulator and pressure‑reducing system malfunctions caused by dissolved water.
- Provides a reproducible functional test (valve freeze time) for product acceptance and risk assessment.
Related standards
- ISO 4257:1988 (Liquefied petroleum gases - Method of sampling) - normative reference for sampling procedures used with this test.
For organizations managing LPG quality or regulator reliability, EN ISO 13758:1996 offers a concise, purpose-built method to screen propane for moisture‑related freezing risks using the valve freeze test.
