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Our customer service department fields many questions that require technical assistance from our sales engineering department. We have compiled some of these and posted them here for easy access. If you do not find the answer to your specific question, or would like additional information, please contact us.

1. Question:

I have a Tiona-Betts PAF Style Manhole/Pressure Relief Valve (PRV) Assembly on an MC306 or DOT406 specification cargo tank that needs to be replaced. What must I do?


Answer: 49CFR178.345-5 requires that manholes on MC306 and DOT406 cargo tanks must be structurally capable of withstanding a 36 psig internal test pressure. Tiona-Betts PAF Manhole PRV assemblies legal for use on MC306 and/or DOT406 cargo tanks are marked as follows.

MEETS DOT 178.345-5

In addition to these markings, Tiona-Betts clamp rings must be stamped on the left bolt lug with "BETTS IND. INC." and on the right bolt lug with "WARREN, PA." If the clamp ring is not so marked, replace it with a new Tiona-Betts clamp ring. These markings must be present on any Tiona-Betts PAF Manhole/PRV Assembly for it to be used as a replacement on an existing tank or for new construction.

Tiona-Betts PAF Style Manhole/PRV Assemblies provide emergency (primary) pressure relief through the 10" Pressure Relief Valve. Insure that the replacement assembly provides adequate venting capacity to meet or exceed the minimum required flow capacity based on the exposed area of the cargo tank (compartment) as defined in 49CFR178.345-10(e).

49CFR180.405 requires that pressure relief devices must not leak more 1 liter of product when subjected to a dynamic surge pressure as defined in 49CFR178.345-10(b). This requirement must be met on both MC306 and DOT406 cargo tanks whenever a replacement PRV is installed. PRV's on MC306 and early DOT406 cargo tanks that do not meet the 1 liter leakage requirement, can remain in service indefinitely so long as they function properly.

All Tiona-Betts PAF406-98 and PAF306-98 meet the 1 liter surge requirement while providing the popular strongback and latch mechanism. Betts also offers a full line of Zero Leakage Manhole Assemblies that do not release any product when subjected to the defined surge. They are available in either a single wing nut openable design or a non-openable bolted design.




2. Question:

I have a Tiona-Betts normal vent (6496AL or 6238AL) that leaks during the annual cargo tank leakage test mandated in 49CFR180.407(h). What should I do?


Answer: 49CFR180.407(h)(1) requires the leakage test pressure to be at least 0.80 x cargo tank M.A.W.P. or tank design pressure. For MC306 tanks, the leakage test pressure is 2.4 psig, and for standard 3.3 psig M.A.W.P. DOT406 cargo tanks the leakage test pressure is 2.64 psig. Both of these pressures are greater than set pressures for either Tiona-Betts normal vents, so they must be removed or rendered inoperative during the leakage test, as required in 49CFR180.407(h)(1).



3. Question:

I have a Tiona-Betts normal vent that leaks during the DOT mandated bench test as part of the cargo tank pressure test. What should I do?



49CFR180.407(g)(1)(ii) requires normal vents and other reclosing pressure relief valves to be bench tested as part of the 5 year cargo tank pressure test. Refer to Engineering Bulletin 1-99 for detailed instructions on test procedures and pressure and vacuum settings for Tiona-Betts normal vents.

Inspect your test apparatus for leaks in fittings. Often times a small leak in the test apparatus will cause false set pressure readings. Generally, normal vents that do not pass the bench test can be brought into compliance by dismantling, cleaning and then assembling




4. Question:

How do I install a PAF style manhole assembly?


Answer: Place the manhole gasket on the top face of the weld collar in the tank. Open the strongback and latch mechanism to relieve pressure on the 7 gage manhole cover plate. Center manhole cover on top of gasket and install clamp ring around perimeter. Install clamp ring bolt, nut and washer and tighten until snug. While tightening, use a non-marking and non-sparking hammer to gently tap around perimeter of clamp ring insure a leak tight seal.



5. Question:

I have a PAF style manhole/pressure relief valve assembly in which the 10" pressure relief valve (often times called the fill cover) does not hold the proper set pressure. What should I do?


Answer: Open the 10" pressure relief valve (PRV) cover and inspect the gasket and seat area for damage, wear or foreign material. Clean gasket and seat. Replace PRV gasket if it is worn or shows signs of degradation.

Next, insure that the PRV is properly adjusted. Refer to Engineering Bulletin "Proper Adjustment of Pressure Relief Valve" for the adjustment procedure on PAF1000, PAF9000, PAF450 or PAF406-92 PRV's. For PAF406-96, PAF406-98 and PAF306-98 PRV's, refer to Engineering Bulletin 4-97 or maintenance manuals for your specific model.

If you are unable to obtain proper set pressure, reinstall manhole on collar following instructions in answer to FAQ #4 and then readjust set pressure.


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