ISO 8316:1987

Overview

ISO 8316:1987 specifies the volumetric tank method for measuring liquid flow in closed conduits by collecting a known volume over a measured time interval. The standard covers apparatus, procedures, calculation of flow‑rate and the evaluation of measurement uncertainty. Because of its high accuracy, the volumetric method is often used as a primary calibration technique for other flow meters and for legal metrology applications.

Key topics and technical requirements

• Measurement principle
  • Two main variants: static gauging (measure level before and after diversion) and dynamic gauging (measure level while filling).
• Apparatus
  • Volumetric tank: typically cylindrical, leak‑proof, designed to minimise wall absorption and distortion; large enough to make timing and level errors negligible.
  • Diverter: must direct flow to tank or bypass without changing flow-rate; rapid travel recommended (e.g., <0.1 s) or, for large flows, a known linear operating law. Nozzle slot pressure drop should be limited (around 20 kPa) to avoid splashing and air entrainment.
  • Level measuring devices: accurate level sensing and a calibrated level–volume relationship (by transferring known volumes or dimensional calibration).
  • Time measurement: accurate electronic timer (quartz) with resolution to 0.01 s or better; timer triggered by diverter motion.
• Performance and limits
  • Typically used for flow-rates up to about 1.5 m3/s and commonly in laboratory/static installations.
  • Expected overall uncertainty can be as low as ±0.1% to ±0.2% (95% confidence) when precautions are followed.
  • Practical guidance: minimum level change ≈ 1 m and minimum filling time at maximum flow ≈ 30 s (can be reduced if verified).
• Uncertainty and corrections
  • Procedures for calculating flow‑rate and assessing combined uncertainty are specified; uncertainty estimation aligns with ISO 5168.
  • Annex A provides corrections for filling-time measurement effects; annexes B–E provide supporting information and examples.

Applications and users

• Calibration laboratories using volumetric methods to certify and calibrate flowmeters.
• National metrology institutes and legal metrology authorities requiring traceable, primary flow measurements.
• Industrial test facilities and R&D labs where high-accuracy liquid flow measurement is needed (meter verification, reference standards).
• Designers of volumetric flow installations and measurement engineers implementing static or dynamic gauging.

Related standards

• ISO 4006 - Vocabulary and symbols for fluid flow in closed conduits.
• ISO 4185 - Weighing method for liquid flow measurement.
• ISO 4373 - Water level measuring devices (open channels).
• ISO 5168 - Estimation of uncertainty in flow‑rate measurement.

Keywords: ISO 8316, volumetric tank, liquid flow measurement, closed conduits, flow‑rate calibration, static gauging, dynamic gauging, diverter, measurement uncertainty.