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A-7 Troubleshooting Techniques

How to verify compartment is empty before loading

Tap on the compartment with a non-metal object and listen for the sound/vibration change. Open belly-valves and check sight glass on each loading head for evidence of product in loading tubes. Climb up on top of tank and open dome lids and visually inspect for product.

No green or permit light at terminal before loading, or losing permit light during loading

Check cord connection. Check for probe lights on loading control box on trailer. Check air pressure reading on gauge in fitting box – should be above 60 PSI. Check brake interlock on rear vapor the make sure it is pushed in far enough to activate permit system.

​​Air Pressure FAQs
How much air pressure is required on the gauge in the fitting box before you are permitted to load? – 60 PSI. What is the optimum pressure you should see on the gauge in fitting box before starting loading process? - Over 100 PSI. 

How to build air pressure back up on trailer

Unhook all loading arms and vapor hose. Drop loading bar down so brakes can be released on trailer. Start tractor and push in red valve to release trailer brakes, rev engine up to 1500rpms and allow trailer pressure to build back, brake tanks must build up to over 80psi before air will start building in the loading service tank, after 2-3 minutes pull red valve back out and check gauge in fitting box, if not over 100psi repeat the air building steps.

Brakes will not unlock after loading/unloading

Check interlock valves on rear vapor connection and loading bar. NOTE: Brakes will not unlock, or trailer will not build air if interlocks or bar valve is still activated.

How to manually operate air or cable-style belly valves

If the cable is broken or slipped, a rachet strap can be connected to the belly valve arm at the belly valve and it can be manually opened by ratchetting the valve arm in the direction the cable is pulling.

Air operated belly valves can be opened by using an Allen wrench to remove the bypass bolt from the belly valve and removing the access plug from the side of the belly valve, screw in the bypass bolt into the access plug hole and it will manually open the valve.

Product flow stopped during unloading

NOTE: The following steps apply when there is product in compartment or storage tank fills up while delivery hoses are securely and properly connected.

Check air pressure on gauge in fitting box, make sure it's above 60 PSI. If not, follow pressure-building techniques for trailer system. Shut off unloading valve and belly valve, place spill pads around spill week to catch product if pushes out of the spill bucket. Climb up on top of tank and stick compartment to assess how many inches of product remain in the compartment. Contact dispatch so they can verify with tank charts how much product remains and where they want it delivered. Correct your delivery gallons on your trip ticket to represent the correct amount you are delivering to that location and make notes of where the retained amount is going and how much will be delivered to the 2nd location. Open one ear on the delivery hose at the unloading head slightly until you hear a vacuum sound, and you see product draining into the tank through the sight glass on your drop fitting. If product begins to push out when you crack open the hose ear (cam lock), close it back and wait 5 minutes for pressure to settle. Once you hear a vacuum sound, open the cam-locks on the hose coupling, disconnect and drain the hose, and remove the fitting from the delivery tube.

Tanker Trailer Components

DOT 406 Design

Tanker trailers designed for petroleum transport are not "high pressure" vessels, but they are equipped to safely contain and haul flammable liquids in bulk quantities. As such, the safeguards and key components are worth noting as they relate to potential troubleshooting of air pressure, electrical, and product flow issues. (Shown is a Civacon equipped tanker trailer for example of how many specialized components there are on a DOT 406 rated trailer.)