[Code of Federal Regulations]
[Title 40, Volume 31]
[Revised as of July 1, 2007]
From the U.S. Government Printing Office via GPO Access
[CITE: 40CFR1065.245]

[Page 708]
 
                   TITLE 40--PROTECTION OF ENVIRONMENT
 
         CHAPTER I--ENVIRONMENTAL PROTECTION AGENCY (CONTINUED)
 
PART 1065_ENGINE-TESTING PROCEDURES--Table of Contents
 
                    Subpart C_Measurement Instruments
 
Sec.  1065.245  Sample flow meter for batch sampling.

    (a) Application. Use a sample flow meter to determine sample flow 
rates or total flow sampled into a batch sampling system over a test 
interval. You may use the difference between a diluted exhaust sample 
flow meter and a dilution air meter to calculate raw exhaust flow rates 
or total raw exhaust flow over a test interval.
    (b) Component requirements. We recommend that you use a sample flow 
meter that meets the specifications in Table 1 of Sec.  1065.205. This 
may involve a laminar flow element, an ultrasonic flow meter, a subsonic 
venturi, a critical-flow venturi or multiple critical-flow venturis 
arranged in parallel, a positive-displacement meter, a thermal-mass 
meter, an averaging Pitot tube, or a hot-wire anemometer. Note that your 
overall system for measuring sample flow must meet the linearity 
verification in Sec.  1065.307. For the special case where CFVs are used 
for both the diluted exhaust and sample-flow measurements and their 
upstream pressures and temperatures remain similar during testing, you 
do not have to quantify the flow rate of the sample-flow CFV. In this 
special case, the sample-flow CFV inherently flow-weights the batch 
sample relative to the diluted exhaust CFV.
    (c) Flow conditioning. For any type of sample flow meter, condition 
the flow as needed to prevent wakes, eddies, circulating flows, or flow 
pulsations from affecting the accuracy or repeatability of the meter. 
For some meters, you may accomplish this by using a sufficient length of 
straight tubing (such as a length equal to at least 10 pipe diameters) 
or by using specially designed tubing bends, orifice plates or 
straightening fins to establish a predictable velocity profile upstream 
of the meter.