Test Procedure 933 (TP-933) is used by the Air Resources Board (ARB) to determine OHRV evaporative emissions. This test procedure is proposed pursuant to section 43824 of the California Health and Safety Code (CH&SC).



This test procedure measures evaporative emissions from a complete vehicle or piece of equipment with complete evaporative emission control systems as defined in 13 CCR 2752 (a)(8) by subjecting them to durability tests, preconditioning, and a diurnal evaporative test as described in section 6 of this procedure. The engine with a complete evaporative emission control system must be tested as a complete vehicle except where a test rig is explicitly allowed. Where not otherwise specified, the vehicle shall be in an approximately level position during all phases of the test sequence.

Prior to evaporative emissions testing, the vehicle’s evaporative emissions control system must undergo durability testing to ensure that the emissions control devices continue to function as designed for the useful life of the vehicle. Real world end of useful life emissions are simulated during vehicle preconditioning. Evaporative emissions are quantified by direct measurement or by a combination of direct measurement and calculation.

Evaporative emissions are directly measured with a hydrocarbon analyzer in a sealed testing enclosure following a defined temperature profile and maintaining atmospheric pressure. The volume of the enclosure must be accurately determined whenever hydrocarbons are being measured. The total mass of hydrocarbons emitted from a test vehicle over the test period is calculated based on measured concentration, known molecular weight, and volume of the testing enclosure. 2 The vehicle shall demonstrate adequate control of diurnal emissions through one of the following test sequences: Vehicle may undergo a 72-hour diurnal evaporative emissions test with variable temperature as defined in section 6.4.1

. Alternatively, a steady state diurnal test may be used to show compliance. The vehicle’s evaporative emissions control system is demonstrated to be adequately designed and constructed by performing a 24-hour diurnal test in conjunction with the vented emissions requirements as described in section 6.4.2. The steady state diurnal test must be conducted with the testing enclosure maintained at a constant temperature of 86°± 3°F, with a vent connecting the evaporative vent of the vehicle to the atmosphere outside the testing enclosure.

The purpose of the steady state diurnal test is to evaluate fuel permeation and verify the construction of the evaporative emissions control system. Compliance is shown with the vented emissions requirement using the Calculation Method as described in Appendix A or by using a pressure relief valve that opens at 2 pounds per square inch (psi) or greater, or which does not release vapor from the tank during the second of two consecutive 24-hour diurnal temperature cycles from 72° to 96°F. A flowchart summarizing the procedure is shown in Figure 1.Type your paragraph here.