Model PAF450, 20″ Offset Manhole, Non-DOT Pressure Relief Device


Model PAF450 incorporates a 10” (254mm) reclosing pressure relief valve (PRV) mounted to an offset 20” (508mm) clamp ring style manhole. It includes a P/V normal vent as well as provisions for mounting a bolted style vapor recovery valve and liquid level sensor. The PRV cover also serves as a quick open inspection hatch that incorporates a secondary safety catch. The manhole and clamp ring are certified and marked in accordance with 49CFR178.345-5 with a test pressure of 36 psig.

The PAF450 was legal for installation on US DOT MC306 cargo tanks prior to August 31, 1998. Per 49CFR180.405(h)(2), a properly functioning PAF450 can be repaired and maintained but if the entire assembly needs to be replaced, it must be a PRV that meets the less-than 1 liter surge leakage requirement of 49CFR178.345(b)(3)(ii). Therefore, Model PAF450 is NOT permitted as a replacement on MC306 or DOT406 cargo tanks but can be installed on non-specification tanks or on tanks built and operated in countries where regulations permit. See Betts’ complete line of PAF406 and PAF306 PRV’s that meet requirements of less-than 1 liter surge leakage.

PAF450 is also available in a self-latch model by designating part number 9863 in place of 9820. On self-latch models, stop bracket holds the PRV at a 91° position; if cover is inadvertently left open, movement of the tank will cause PRV cover to drop and catch to a semi-closed position. Standard model can be converted to a self-latching model with addition of 6807SL-KIT1.

Manuals & Tech Info

The following is a list of available maintenance and installation manuals, technical and engineering bulletins, and specification sheets for this product line.  If you cannot find what you are looking for, please contact one of Betts’ Customer Service Representatives for further assistance.

Maintenance Manual MM-PRV003 (7.11MB)

Installation of Tiona Betts Clamp Ring Style Manhole Assemblies EB1-08.pdf


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 “008” – Includes two normal vents.

Suffix “045” – Includes 6234 in-breathing vent.

Suffix “059” – With padlock loop.