The space reserved for overflow control in current tanks equipped with either radar sensors or gauge boards extends 18-5/8 inches below the inside top bulkhead. This space is equal to 1088 gallons of asphalt. In the past different amounts of empty space have been reserved.
The best way to make sure how much reserved space is used for overflow control in your tank is to fill the tank until the overflow control shuts off the unloading pump. Then measure the vertical distance from the bulkhead inside the tank to the surface of the liquid asphalt. Each inch of height is equivalent to 58.8 gallons of asphalt. So multiply the measured distance by 58.8 to determine the actual volume of the reserved space. If the volume determined from your measurement is different from that shown in Figure 2, go by yours instead. You should also adjust the net volume shown in Figure 2 based on your findings.
The amount of space reserved for overflow control depends on the devices used for high-level control and how they are setup. Gauge boards have a high level switch near the bottom of the gauge board. When activated the switch shuts off the unloading pump to prevent overflowing the tank. It is activated by the bulls eye that travels up and down the gauge board to indicate levels. The exact location of the switch on the gauge board governs shutoff level. Changing its location changes the shutoff level.
Radar sensors also shutoff unloading pumps at a specific level, usually the same level as the shutoff on the gauge board. This level is governed by the settings made on the Honeywell controller used with the sensor to indicate asphalt levels. The settings can be changed to change the shutoff level.
A high-level float switch is built into all vertical tanks to serve as a backup to the gauge board and radar sensor. It shuts off the unloading pumps at a slightly higher level than either the gauge board high level switch or the radar high level control.
CONVERTING LEVELS TO VOLUMES
Figure 5 converts levels to volume or gallons of asphalt thereby indicating how much asphalt is stored in the tank.
It is important to understand that the levels shown in Figure 5 refer to the height of the liquid above the inside bottom of the tank. You should also be aware that levels indicated by radar sensors and gauge boards also refer to the height of the liquid above the inside bottom of the tank.
Do not confuse these levels with the distance found by extending a measuring tape through the manway at the top of the tank until it touches the asphalt. That is a measure of empty space in the top of the tank—not how much asphalt is in the tank.
However, you can use your measuring tape or “stick” measurement of empty space to determine the amount of asphalt in your tank (see Figure 3). To do so, note the inside height of your tank as listed in Figure 4. Subtract your measurement from that height. This gives you the level of the asphalt above the bottom of the tank. You can now use this level with Figure 5 to determine the gallons of asphalt stored in your tank.
Figure 3. Making measurements from manway.
Note: When making your measurement it is difficult to measure directly from the inside top surface of the tank to the asphalt surface. It is much easier to measure from the bottom edge of the manway to the surface of the asphalt. If you do that you will need to make a separate measurement to determine the distance from the edge of the manway to the topmost surface inside the tank. Then you should add the two measurements together.
Figure 5 applies to all sizes of Heatec vertical tanks. For your convenience, the first three columns shows each level three different ways. The first column shows only inches. The second column shows feet and tenths of a foot. The third column shows feet and inches.
Note that the third column shows feet as a whole number and inches as a fraction of twelve. This is the way our computer program handles feet and inches. It makes perfect sense even though it may not be the way you are used to seeing feet and inches written. The fourth column shows gallons for each level.
Levels for the radar sensor are shown in tenths of a foot, so the second column will be more convenient for its levels. But gauge boards show levels in feet and inches, so the third column would be more convenient for them.
The amount of space or volume displaced by the heating coils has not been deducted from the gallons shown in column 4. So, if you need to know exactly how much asphalt is in your tank, be sure to deduct the volume displaced by the coils.
The volumes displaced by the heating coils are shown in Figure 2. When the asphalt level totally covers the coils, deduct the full amount of the amount shown in the Figure. When levels are below the tops of the coils, you may wish to deduct a smaller amount based on your best estimate.
Note, unlike horizontal tanks, volumes in vertical tanks are in direct proportion to the levels. The volume increases or decreases 58.8 gallons for each inch of change in level.
