Council Directive of 20 March 1970 on the approximation of the laws of the Member States on measures to be taken against air pollution by emissions from motor vehicles (70/220/EEC) (repealed)

[F1 4.2. Calibration of the positive displacement pump (PDP) U.K.

4.2.1. The following calibration procedure outlines the equipment, the test configuration and the various parameters which are measured to establish the flow-rate of the CVS pump. All the parameters related to the pumpare simultaneously measured with the parameters related to the flow-meter which is connected in series with the pump. The calculated flow-rate (given in m ³ /min at pump inlet, absolute pressure and temperature) can then be plotted versus a correlation function which is the value of a specific combination of pump parameters. The linear equation which relates the pump flow and the correlation function is then determined. In the event that a CVS has a multiple speed drive, a calibration for each range used must be performed. U.K.

4.2.2. This calibration procedure is based on the measurement of the absolute values of the pump and flow-meter parameters that relate the flow-rate at each point. Three conditions must be maintained to ensure the accuracy and integrity of the calibration curve. U.K.

4.2.2.1. The pump pressures must be measured at tappings on the pump rather than at the external piping on the pump inlet and outlet. Pressure taps that are mounted at the top centre and bottom centre of the pump drive headplate are exposed to the actual pump cavity pressures, and therefore reflect the absolute pressure differentials. U.K.

4.2.2.2. Temperature stability must be maintained during the calibration. The laminar flow-meter is sensitive to inlet temperature oscillations which cause the data points to be scattered. Gradual changes of ± 1 K in temperature are acceptable as long as they occur over a period of several minutes. U.K.

4.2.2.3. All connections between the flow-meter and the CVS pump must be free of any leakage. U.K.

4.2.3. During an exhaust emission test, the measurement of these same pump parameters enables the user to calculate the flow-rate from the calibration equation. U.K.

4.2.3.1. Figure III.6.4.2.3.1 of this Appendix shows one possible test set-up. Variations are permissible, provided that they are approved by the authority granting the approval as being of comparable accuracy. If the set-up shown in Figure III.5.3.2 of Appendix 5 is used, the following data must be found within the limits of precision given: U.K.

barometric pressure (corrected) (PB)	± 0,03 kPa
ambient temperature (T)	± 0,2 K
air temperature at LFE (ETI)	± 0,15 K
pressure depression upstream of LFE (EPI)	± 0,01 kPa
pressure drop across the LFE matrix (EDP)	± 0,0015 kPa
air temperature at CVS pump inlet (PTI)	± 0,2 K
air temperature at CVS pump outlet (PTO)	± 0,2 K
pressure depression at CVS pump inlet (PPI)	± 0,22 kPa
pressure head at CVS pump outlet (PPO)	± 0,22 kPa
pump revolutions during test period (n)	± 1 rev
elapsed time for period (minimum 250 s) (t)	± 0,1 s.

4.2.3.2. After the system has been connected as shown in Figure III.6.4.2.3.1, set the variable restrictor in the wide-open position and run the CVS pump for 20 minutes before starting the calibration. U.K.

4.2.3.3. Reset the restrictor valve to a more restricted condition in an increment of pump inlet depression (about 1 kPa) that will yield a minimum of six data points for the total calibration. Allow the system to stabilize for three minutes and repeat the data acquisition. U.K.

PDP-CVS calibration configuration

4.2.4. Data analysis U.K.

4.2.4.1. The air flow-rate (Q _s ) at each test point is calculated in standard m ³ /min from the flow-meter data using the manufacturer's prescribed method. U.K.

4.2.4.2. The air flow-rate is then converted to pump flow (V _o ) in m ³ /rev at absolute pump inlet temperature and pressure. U.K.

where:

V _o

=

pump flow-rate at T _p and P _p given in m ³ /rev,

Q _s

=

air flow at 101,33 kPa and 273,2 K given in m ³ /min,

T

=

pump inlet temperature (K),

P _p

=

absolute pump inlet pressure,

n

=

pump speed in revolutions per minute.

To compensate for the interaction of pump speed pressure variations at the pump and the pump slip rate, the correlation function (X _o ) between the pump speed (n), the pressure differential from pump inlet to pump outlet and the absolute pump outlet pressure is then calculated as follows:

where:

X _o

=

correlation function,

ΔP _p

=

pressure differential from pump inlet to pump outlet (kPa),

P _e

=

absolute outlet pressure (PPO + P _B (kPa).

A linear least-square fit is performed to generate the calibration equations which have the formulae:

D _o , M, A and B are the slope-intercept constants describing the lines.

4.2.4.3. A CVS system that has multiple speeds must be calibrated on each speed used. The calibration curves generated for the ranges must be approximately parallel and the intercept values (D _o ) must increase as the pump flow range decreases. U.K.

If the calibration has been performed carefully, the calculated values from the equation will be within ± 0,5 % of the measured value of V _o . Values of M will vary from one pump to another. Calibration is performed at pump start-up and after major maintenance.]

Textual Amendments

F1 Substituted by Council Directive of 26 June 1991 amending Directive 70/220/EEC on the approximation of the laws of the Member States relating to measures to be taken against air pollution by emissions from motor vehicles (91/441/EEC).