Model PAF 306-98, 20″ Offset Manhole, MC306 Replacement Pressure Relief Device

  • REPLACEMENT FOR PAF9000 MODELS
  • INTEGRAL 10” FILL/PRESSURE RELIEF
  • VALVE WITH MC306 SET PRESSURE
  • LESS THAN 1 LITER LEAKAGE
  • SECONDARY SAFETY LATCH

Pressure Relief Valve setting 3.0 psig
Rated Pressure Actuated Emergency Venting:
250,000 cu. ft. free air per hour @ 5.0 psig
Rated Liquid Flow Capacity 1012 gpm @ 5.0 psig

PAF manholes with integral latch style surge suppression relief valves are designed for use as a replacement for PAF9000 model manhole assemblies on MC306 tanks. Manholes are certified and marked in accordance with 49CFR178.345-5 with a test pressure of 36 psig. Manhole covers are 7 gage steel or stainless and are secured to the tank weld collar with a clamp ring and bolt which can be easily removed to provide access into the tank.

The integral 10” relief valve provides emergency pressure relief and meets the 1 liter surge leakage limit imposed by 49CFR178.345-10(b)(3)(ii). The relief valve also serves as a 10” latch style fill which can be easily opened to provide access for filling the tank or for inspection. Relief valves contain an adjustment feature to allow for fine-tuning of set pressure in the field. Other standard features include a heavy duty clamp ring, secondary safety latch and model 6238ALB pressure-vacuum vent mounted in the 10” relief valve cover.

Manholes are available with a self-latching feature that allows the 10” relief valve/fill cover to drop and securely latch upon movement of the tank if the cover is inadvertently left open. For self-latching model substitute R563 for R520 in assembly number.

Parts List

Product Details

NOTE: 3 1/2″ Vent and Liquid Level Switch not included in assembly.

Assembly No.Cover PlateRelief ValveClamping Ring, Bolt, Washer, Strongback, & LatchClamping Ring NutNormal VentWt. (lb.)
FVAR520BXBSteel Zinc Plt.Alum.Steel Zinc Plt.BrassAlum.29.7
FVAR520CXBStnls 304Alum.Stnls 304Stnls 304Alum.30.2
FVAR520DXBStnls 316Alum.Stnls 304Stnls 304Alum.30.2
Note: Manhole assemblies, as listed above, have Buna-N gaskets (suffix "B"). For variation in gasketing change last letter of assembly number as follows:

Suffix "V" indicates Viton collar gasket & Viton 10" fill gasket
Suffix "W" indicates White Hypalon collar gasket & White Hypalon 10" fill gasket
Suffix "T" indicates Teflon envelope collar gasket & Tef-Sil 10" fill o-ring

Manhole collars are available in aluminum, steel, and stainless steel. Please see parts page for correct numbers.
When welding collars to tank, care should be exercised to insure collar remains flat and round.

Engineering Bulletins

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