[Code of Federal Regulations]
[Title 46, Volume 1]
[Revised as of January 1, 2007]
From the U.S. Government Printing Office via GPO Access
[CITE: 46CFR39.20-11]

[Page 514]
 
                           TITLE 46--SHIPPING
 
         CHAPTER I--COAST GUARD, DEPARTMENT OF HOMELAND SECURITY
 
PART 39_VAPOR CONTROL SYSTEMS--Table of Contents
 
                   Subpart 39.20_Design and Equipment
 
Sec. 39.20-11  Vapor overpressure and vacuum protection--TB/ALL.

    (a) The cargo tank venting system required by Sec. 32.55 of this 
chapter must:
    (1) Be capable of discharging cargo vapor at 1.25 times the maximum 
transfer rate such that the pressure in the vapor space of each tank 
connected to the vapor collection system does not exceed:
    (i) The maximum design working pressure for the tank, or
    (ii) If a spill valve or rupture disk is fitted, the pressure at 
which the device operates;
    (2) Not relieve at a pressure corresponding to a pressure in the 
cargo tank vapor space of less than 1.0 psig;
    (3) Prevent a vacuum in the cargo tank vapor space, whether 
generated by withdrawal of cargo or vapor at maximum rates, that exceeds 
the maximum design vacuum for any tank connected to the vapor collection 
system; and
    (4) Not relieve at a vacuum corresponding to a vacuum in the cargo 
tank vapor space of less than 0.5 psi below atmospheric pressure.
    (b) Each pressure-vacuum relief valve must:
    (1) Be tested for venting capacity in accordance with paragraph 
1.5.1.3 of API 2000; and
    (2) Have a means to check that the device operates freely and does 
not remain in the open position, if installed after July 23, 1991.
    (c) The relieving capacity test required by paragraph (b)(1) of this 
section must be carried out with a flame screen fitted at the vacuum 
relief opening and at the discharge opening if the pressure-vacuum 
relief valve is not designed to ensure a minimum vapor discharge 
velocity of 30 meters (98.4 ft.) per second.