Model PAF450, 16″ Offset Manhole, Non-DOT Pressure Relief Device

Model PAF450 incorporates a 10” (254mm) reclosing pressure relief valve (PRV) mounted to an offset 16” (406mm) clamp ring style manhole. It includes a P/V normal vent as well as provisions for mounting a 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 9842 in place of 9816. 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.

Parts List

Product Details

Material of Construction

Part #Manhole CoverStrongback and LatchPRV CoverNormal VentWeight
FVA9816BX*Steel Zinc PlatedSteel Zinc PlatedAluminum6238AL Aluminum22.6 lbs. (13.5 kg)
FVA9816CX*304 Stainless304 StainlessAluminum6238AL Aluminum22.6 lbs. (13.5 kg)
FVA9816DX*316 Stainless304 StainlessAluminum6238AL Aluminum22.6 lbs. (13.5 kg)
* Last letter of part number designates seal material. See gasket material table.

LetterGasket Material
BNitrile (Buna-N)
WWhite Hypalon
TPTFE (w/ Nitrile or Silicone Core)
VFKM Type A

  • Use part number FVA9842 for self-latch.
  • Suffix “059” option for padlock loop installed in strongback.
  • Prefix “FSA” for both 6238AL normal vent & 6234AL inbreathing vent included.
  • Weld Collar NOT included with assembly, but available separately as shown in part list. Collar material should correspond with tank shell material. When welding collars to tank, care should be taken to insure collar remains flat and round with use of a welding fixture if necessary.

Technical Specifications

PAF450 Pressure Relief Valve6238AL Normal Vent (P/V Vent)
Set PressureRelated Air Flow Capacity
(Cubic feet per hour)
Pressure SetPressure Rated Flow CapacityVacuum SetVacuum Flow Capacity
Min 3.0 psig
(Min 20.7 kPa)
375,000 SCFH @ 5 psig
(10.618 SCMH @ 34.5 kPa)
Max 1.0 psig
(max 6.8 kPa)
1,750 SCFH @ 3 psig
(49 SCMH @ 20.7 kPa)
Max .375 psig
(Max 2.5 kPa)
3,350 SCFH @ 1 psig
(95 SCMH @ 6.8 kPa)

Engineering Bulletins

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