ISO 4185:1980

Overview

ISO 4185:1980 - Measurement of liquid flow in closed conduits - Weighing method defines a primary laboratory method for measuring liquid flow by collecting and weighing the mass of liquid delivered into a tank during a known time interval. The standard covers apparatus, procedures, calculation of mass and volume flow-rate, and estimation of measurement uncertainty. It excludes corrosive or toxic liquids and situations where vaporization from the weighing tank would affect accuracy.

Key Topics and Requirements

• Principle (static and dynamic weighing)
  • Static weighing: tare and gross weighings before and after diverting flow into the weighing tank.
  • Dynamic weighing: continuous weighing while flow is delivered to the tank; no diverter required.
• Essential apparatus
  • Diverter: fast-acting baffle or nozzle divider (typical travel < 0.1 s) to switch flow to the tank with minimal disturbance. Nozzle sheet length typically 15–50× its width; pressure drop across nozzle should not exceed ~20 000 Pa.
  • Weighing tank: sufficient capacity so highest flow produces a filling time generally ≥ 30 s (or verified experimentally if shorter).
  • Weighing machine: calibrated over the full range with standard weights; buoyancy correction required because of differences between calibrated weights and liquid.
  • Time-measuring apparatus: accurate electronic timer (quartz-referenced) actuated by diverter motion; resolution typically 0.01 s or better.
• Measurement conditions
  • Pipeline must run full with no air/vapor pockets.
  • Avoid vaporization or leaks; thermal expansion/accumulation must be negligible or corrected.
  • Method works for liquids with sufficiently low vapor pressure and typical flow velocities up to ~1.5 m/s in hydraulic labs.
• Uncertainty and calibration
  • When properly applied, ISO 4185 can achieve very high accuracy - random-part uncertainty on the order of ±0.1% (95% confidence) is attainable.
  • Installations used for legal metrology should be certified by the national metrology service and undergo periodic inspection.

Applications and Users

• Calibration laboratories and national metrology institutes using the weighing method as a primary standard to calibrate flowmeters and validate other flow measurement methods.
• Hydraulic test facilities, pump and turbine test labs, and manufacturers needing high-accuracy mass or volume flow-rate reference measurements.
• Useful for volume-to-mass conversions when liquid density is accurately known and for traceable measurement chains in research and quality assurance.

Related Standards

• ISO 4006 - Measurement of fluid flow in closed conduits: Vocabulary and symbols.
• ISO 5168 - Measurement of fluid flow - Estimation of uncertainty of a flow-rate measurement.
• OIML Recommendations referenced in the standard for weighing instrument practice and calibration.

Keywords: ISO 4185:1980, weighing method, measurement of liquid flow, closed conduits, mass flow-rate, flowmeter calibration, uncertainty, diverter, weighing tank, buoyancy correction, legal metrology.