{
  "url": "https://openlegislation.uk/eu-regulation-2017-654/annex-VII/division-2/division-2.5/division-2.5.3",
  "json_url": "https://openlegislation.uk/eu-regulation-2017-654/annex-VII/division-2/division-2.5/division-2.5.3.json",
  "legislation": "eur/2017/654",
  "legislation_title": "Commission Delegated Regulation (EU) 2017/654 of 19 December 2016 supplementing Regulation (EU) 2016/1628 of the European Parliament and of the Council with regard to technical and general requirements relating to emission limits and type-approval for internal combustion engines for non-road mobile machinery",
  "legislation_url": "https://openlegislation.uk/eu-regulation-2017-654",
  "path": "annex/VII/division/2/division/2.5/division/2.5.3",
  "kind": "division",
  "number": "2.5.3",
  "heading": "Subsonic venturi (SSV)",
  "text": "Calibration of the SSV is based upon the flow equation for a subsonic venturi. Gas flow is a function of inlet pressure and temperature, pressure drop between the SSV inlet and throat, as shown in equation (7-40).\nThe airflow rate (qV SSV) at each restriction setting (minimum 16 settings) shall be calculated in standard m3/s from the flowmeter data using the manufacturer's prescribed method. The discharge coefficient shall be calculated from the calibration data for each setting by means of equation (7-73):\nC d = q V SSV A 0 60 d 2 V p p 1 T in,V r 1,4286 p − r 1,7143 p 1 1 − r 4 D r 1,4286 p\n(7-73)\nWhere:\nA 0 collection of constants and units conversions = 0,0056940 m 3 min × K 1 2 kPa × 1 mm 2\nqV SSV air flow rate at standard conditions (101,325 kPa, 273,15 K) [m3/s]\nT in,V temperature at the venturi inlet [K]\nd V diameter of the SSV throat [mm]\nr p ratio of the SSV throat to inlet absolute static pressure = 1 – Δp/p p [-]\nr D ratio of the SSV throat diameter, d V, to the inlet pipe inner diameter D [-]\nTo determine the range of subsonic flow, C d shall be plotted as a function of Reynolds number Re, at the SSV throat. The Re at the SSV throat shall be calculated by means of equation (7-74):\nR e = A 1 × 60 × q V SSV d V × μ\n(7-74)\nwith\nμ = b × T 1,5 S + T\n(7-75)\nWhere:\nA1 collection of constants and units conversions = 27,43831 Kg m 3 × min s × mm m\nqV SSV air flow rate at standard conditions (101,325 kPa, 273,15 K) [m3/s]\nd V diameter of the SSV throat [mm]\nμ absolute or dynamic viscosity of the gas [kg/(m · s)]\nb 1,458 × 106 (empirical constant) [kg/(m · s · K0,5)]\nS 110,4 (empirical constant) [K]\nBecause qV SSV is an input to the Re equation, the calculations shall be started with an initial guess for qV SSV or C d of the calibration venturi, and repeated until qV SSV converges. The convergence method shall be accurate to 0,1 % of point or better.\nFor a minimum of sixteen points in the region of subsonic flow, the calculated values of C d from the resulting calibration curve fit equation shall be within ± 0,5 % of the measured C d for each calibration point.",
  "extent": "E+W+S+N.I.",
  "status": null,
  "version": "current",
  "annotations": [],
  "outstanding_effects": [],
  "provenance": {
    "source": "legislation.gov.uk",
    "source_url": "https://www.legislation.gov.uk/eur/2017/654/annex/VII/division/2/division/2.5/division/2.5.3",
    "retrieved_at": "2026-11-01T14:45:01.864924+00:00"
  },
  "licence": "Open Government Licence v3.0",
  "licence_url": "https://www.nationalarchives.gov.uk/doc/open-government-licence/version/3/",
  "attribution": "Contains public sector information licensed under the Open Government Licence v3.0. Source: legislation.gov.uk, The National Archives."
}