406 and 306 Pressure/Vacuum Normal Vent

  • Dual Purpose Vent
  • Roll Over Protection
  • Compact Design
  • Interior Mount

The Betts’ Normal Vent is the proven standard of the fuel transport industry. Normal Vents (breather vents) are utilized to normalize internal tank vacuum and pressure, which is critical to keep the cargo tank pressure within safe design limits. This vent incorporates a unique weighted roll-over block which increases the set pressure of the vent in a roll over situation but does not act as a shutoff device like other manufacturer’s designs. This feature differentiates the Betts’ design and allows the vent to maintain its primary function as a pressure/vacuum relief device in all situations. The vent is flow tested and marked in accordance with DOT requirements.

Two standard vent styles are available; one for MC306 cargo tanks and the other for DOT406 cargo tanks. Model 6496, DOT406 style, has a pressure setting per 178.346-3(b)(2) of “not less than 1 PSIG” and a vacuum setting per 178.346-3(c)(2) of “no more than 6 ounces”.

NOTE: While normal vents provide limited vapor venting during loading/unloading, it is recommended that positive vapor valves (typically air operated) be provided when loading/unloading with the manhole closed. If positive vapor valves are not used, insure normal vent is functioning properly or open manhole cover before beginning loading/unloading. Failure to do so may result in head reversals or other tank failure.


Parts List

Product Details

Part #DescriptionMounting
Set Pressure**
(Out Breathing)
Pressure Flow Capacity
(Out Breathing)
Vacuum Set**
(In Breathing)
Vacuum Flow Capacity
(In Breathing)
6238AL*MC306 Normal Vent (FVA)1 5/8-12UNAlum.0.65 to 1.0 psig1,750 CFH @ 3 psi0.25 to 0.375 psig3,350 CFH @ 1 psi1.0 lb.
6238SL*MC306 Normal Vent (FVA)1 5/8-12UN303 SS0.65 to 1.0 psig1,750 CFH @ 3 psi0.25 to 0.375 psig3,350 CFH @ 1 psi2.5 lbs.
6496AL*DOT406 Normal
Vent (PPV)
1 5/8-12UNAlum.1.0 to 1.75 psig1,200 CFH @ 3 psi0.25 to 0.375 psig3,350 CFH @ 1 psi1.0 lb.
6496SL*DOT406 Normal
Vent (PPV)
1 5/8-12UN303 SS1.0 to 1.75 psig1,200 CFH @ 3 psi0.25 to 0.375 psig3,350 CFH @ 1 psi2.5 lbs.
* Replace with letter code to designate seal material.
** Proper maintenance is required to ensure effective performance of normal vent. Dust, dirt, or residue will reduce the ability of the vent to hold required set-pressure.
Letter CodeMaterialTemperature Range***
BBuna-N-40°F to +220°F
VFKM Type A (Viton®)-20°F to +400°F
VBFKM Type B-20°F to +400°F
FSFluorosilcone-50°F to +300°F
EPEPDM (Black)-40°F to +260°F
WEEPDM (White FDA)-40°F to +260°F
*** Values shown are test values. Actual values may vary due to service conditions

Additional Options

Betts prides itself in being able to provide products that meet a customer’s specific needs. As a result we do offer modifications to our product standards. While not every request is always feasible, we do our best to meet your specific needs. In many cases this modification is noted by adding a suffix to the end of the standard part number. The following is a non-inclusive list of common options that are available for this product line . If the options listed below do not meet your requirements please contact one of Betts’ Customer Service Representatives for further assistance. Please note that some product modifications may result in extended lead times.

Commonly Requested Options:

Suffix “277” – Normal vent with 35x35x.012 screen. Image 6496AL_277

Engineering Bulletins

EB-01-22: Breather Vent Overturn Protection ADR/EN Requirement and Compliance