TANK VENT/OVERFLOW PIPE

Proper maintenance of the vent/overflow pipe is crucial to safe operation of the tank. Failure to maintain this pipe could lead to either rupturing or collapsing the tank.

A 4-inch pipe installed inside the tank serves as a vent/overflow pipe (Fig. 1). Both ends are open. Its top end is positioned just below the inside top head of the tank. Its bottom end turns outboard just above the heating coils, goes through the side of the tank and turns down. It ends several inches above the ground and is painted red for easy identification (Fig. 16).

Figure 16. Overflow pipe at bottom of tank.

It is extremely important to make sure that this pipe never gets stopped up or restricted in any way. If this pipe ever becomes restricted or stopped up, pumping asphalt into the tank leaves no way for air displaced by the incoming asphalt to escape. Consequently, air pressure inside the tank could build up and rupture the tank with disastrous consequences.

Conversely, pumping asphalt from the tank that has a stopped up vent could reduce the pressure inside the tank creating somewhat of a vacuum. Consequently, the reduced pressure could cause the walls of the tank to collapse.

Fumes from asphalt inside the tank sometimes have a tendency to build up a residue in the pipe, especially near the bottom end of the pipe where the pipe turns and comes out of the tank.

One clue to a clogged vent is the sound of air escaping the bottom end of the pipe when the tank is being filled with asphalt. A strong, steady stream of air escaping from an unclogged pipe as the tank is filled has a distinct sound. It is usually a good indication that the vent is clear. But if you detect changes in the usual sound or flow of air from the vent, it may be clogged or partially so.

You may be able to unclog the pipe without opening the tank or going inside the tank. If you suspect the vent may be clogged, remove the red elbow and short piece of red pipe from the bottom of the tank. Make sure these two items are clear of any obstructions. Then check the vent pipe still protruding from the tank and its elbow just inside the tank. You may need to use a short rod to prod the elbow to determine if it is okay.

MANHOLES

Vertical asphalt tanks normally have two manholes, one on top of the tank and another in the side of the tank, close to the ground. The manhole on top of the tank is a hinged cover plate that is secured with a quick-release locking lever (Fig. 17). The one at the bottom of the tank is secured with a cover plate and that is bolted into place. The manhole on top of the tank can be opened while there is liquid in the tank. However, the opening should only be used for looking inside the tank. It is not an entrance way and no ladder is provided. Anyone looking inside the tank while it contains liquid asphalt should keep their face well above the opening.

Figure 17. Gasket on manhole cover plate should provide air-tight seal.

Maintenance of this manhole consists of two checks. First, check the locking lever to make sure it is functional and free of damage. Second, check the gasket inside the cover plate to make sure it is not damaged and that it completely seals the opening so that no fumes escape when the cover plate is closed and the lever is locked in place (Fig. 18). You can be sure that the cover plate is not sealed if you find a lot of residue around the manhole.

Figure 18. Gasket on manhole cover plate should provide airtight seal.

The manhole near the bottom of the tank is sealed with a large steel cover that is bolted into place. Never remove this cover while there is hot asphalt inside the tank. After the tank has been emptied and is cold, this manhole can be used to enter the tank for maintenance or repair. All of the safety requirements set forth in OSHA regulations should be strictly followed before anyone enters the tank. A new gasket should be installed when the cover plate is re-installed.

Horizontal asphalt tanks normally have one manhole for each compartment. They have hinged cover plates with locking levers, the same as those on top of vertical tanks. Each opening should only be used for looking inside the tank when the tank compartment contains liquid asphalt. Again, anyone looking inside a tank compartment while it contains liquid asphalt should keep their face well above the opening. After all tank compartments have been emptied and are cold the manholes can be used to enter the compartments for maintenance or repair. All of the safety requirements set forth in OSHA regulations should be strictly followed before anyone enters the tank.

Maintenance of the manholes on horizontal tanks is the same as for those on top of vertical tanks as described above.