Model 820 PAF 406-98, 20″Offset Manhole, DOT 406 Pressure Relief Device

Betts PAF manhole with integral 406-98 Surge Suppression Pressure Relief Valve is the proven leader for cargo tank longevity, protection and safety.

The 406-98 incorporates a 10” (254mm) reclosing pressure relief valve (PRV) that satisfies primary pressure relief for specification US DOT406 and TC406 cargo tanks.  The PRV meets the dynamic pressure surge requirements of 49CFR§178.345-10(b)(3)(ii) with less than one-liter leakage as tested per TTMA RP No. 81.  The PRV cover also serves as a quick-open inspection hatch that incorporates a secondary safety catch. PPVL models include a 6496 P/V normal vent.

The offset 20” (508 mm) clamp ring style manhole has provisions for mounting a bolted style vapor recovery valve and liquid level sensor. Manhole and clamp ring are certified and marked in accordance with 49CFR178.345-5 with a test pressure of 36 psig.

PAF 406-98 is also available in a self-latch model by designating part number L863 in place of L820. On self-latch models, a stop bracket holds the PRV at a 91° position; if the cover is inadvertently left open, movement of the tank will cause PRV cover to drop and catch to a semi-closed position.

PAF 406-98 PRV must not exceed a maximum temperature of 212°F (100°C).  Stainless versions of the PRV are available using prefix “PPSS”.  For replacement on MC306 cargo tanks, see Betts’ line of PAF306 surge manholes.


Product Details

Part #Manhole CoverStrongback and LatchPRV CoverNormal VentWeight
PPVL820AX*AluminumSteel Zinc-platedE-Coated Aluminum6496AL Aluminum22.6 lbs [10.3 kg]
PPVL820BX*Steel Zinc-platedSteel Zinc-platedE-Coated Aluminum6496AL Aluminum30.2 lbs [13.7 kg]
PPVL820CX*304 Stainless304 StainlessE-Coated Aluminum6496AL Aluminum30.2 lbs [13.7 kg]
PPVL820DX*316 Stainless304 StainlessE-Coated Aluminum6496AL Aluminum30.2 lbs [13.7 kg]
* Last letter of part number designates seal material. See gasket material table.

  • Use part number PPVL863 for self-latch unit.

  • Suffix "059" option for padlock loop installed in strongback.

  • Prefix "PSA" for both 6496 normal vent & 6234AL inbreathing vent included.

  • Suffix "092" option with stainless hardware (strongback and latch).

  • Weld Collar NOT included with assembly. 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.

LetterGasket Material
BNitrile (Buna-N)
VFKM Type A (Viton™ A)
TPTFE (w/ Nitrile or Silicone Core)
WWhite Hypalon
See catalog page S80P0A for full list.
Technical Specifications
PAF 406-98 Pressure Relief Valve
Set Pressure (PRV Designed for 3.3 psig MAWP tank)Min. 3.63 psig [25.0 kPa]Max. 4.55 psig [31.4 kPa]
Rated Air Flow Capacity494,084 SCFH @ 6.25 psig [13,992 SCMH @ 43.1 kPa]
294,985 SCFH @ 5psig [8,353 SCMH @ 34.5 kPa]
Liquid Flow Capacity1,335 gpm @ 5.0 psig [5,053 lpm @ 34.5 kPa]
6496AL Normal Vent (P/V Vent)
PressureSet 1.0 psig [6.9 kPa]Flow Capacity 1,200 SCFH @ 3 psig [34 SCMH @ 20.7 kPa]
VacuumSet Max .375 psig [Max 2.6 kPa]Flow Capacityv 3,350 SCFH @ 1 psig [95 SCMH @ 6.9 kPa]

Repair Kits and Accessories

Weld Collar and Gasket options

Installation & Maintenance

PAF 406-98 Maintenance Manual

Engineering Bulletins

EB-01-08: Installation of Tiona Betts Clamp Ring Style Manhole Assemblies.

EB-01-18: Regulatory Instructions: Replacement of Pressure Relief Valves on MC306 Tanks.


Clamp-ring Style Manhole Installation Video #MV-PRV001