40 CFR § 1065.644 - Vacuum-decay leak rate.

---
identifier: "/us/cfr/t40/s1065.644"
source: "ecfr"
legal_status: "authoritative_unofficial"
title: "40 CFR § 1065.644 - Vacuum-decay leak rate."
title_number: 40
title_name: "Protection of Environment"
section_number: "1065.644"
section_name: "Vacuum-decay leak rate."
chapter_name: "ENVIRONMENTAL PROTECTION AGENCY"
subchapter_number: "U"
subchapter_name: "AIR POLLUTION CONTROLS"
part_number: "1065"
part_name: "ENGINE-TESTING PROCEDURES"
positive_law: false
currency: "2026-03-24"
last_updated: "2026-03-24"
format_version: "1.1.0"
generator: "[email protected]"
authority: "42 U.S.C. 7401-7671q."
regulatory_source: "70 FR 40516, July 13, 2005, unless otherwise noted."
cfr_part: "1065"
---


# 1065.644 Vacuum-decay leak rate.

This section describes how to calculate the leak rate of a vacuum-decay leak verification, which is described in § 1065.345(e). Use the following equation to calculate the leak rate, , and compare it to the criterion specified in § 1065.345(e):

Eq. 1065.644-1

Where:

*V*<sub>vac</sub> = geometric volume of the vacuum-side of the sampling system.

*R* = molar gas constant.

*p*<sub>2</sub> = vacuum-side absolute pressure at time t<sub>2.</sub>

*T*<sub>2</sub> = vacuum-side absolute temperature at time t<sub>2.</sub>

*p*<sub>1</sub> = vacuum-side absolute pressure at time t<sub>1.</sub>

*T*<sub>1</sub> = vacuum-side absolute temperature at time t<sub>1.</sub>

*t*<sub>2</sub> = time at completion of vacuum-decay leak verification test.

*t*<sub>1</sub> = time at start of vacuum-decay leak verification test.

Example:

*V*<sub>vac</sub> = 2.0000 L = 0.00200 m
<sup>3</sup>

*R* = 8.314472 J/(mol·K) = 8.314472 (m
<sup>2</sup>·kg)/(s
<sup>2</sup>·mol·K)

*p*<sub>2</sub> = 50.600 kPa = 50600 Pa = 50600 kg/(m·s
<sup>2</sup>)

*T*<sub>2</sub> = 293.15 K

*p*<sub>1</sub> = 25.300 kPa = 25300 Pa = 25300 kg/(m·s
<sup>2</sup>)

*T*<sub>1</sub> = 293.15 K

*t*<sub>2</sub> = 10:57:35 a.m.

*t*<sub>1</sub> = 10:56:25 a.m.

[89 FR 29808, Apr. 22, 2024]