HEATEC TEC-NOTE. Portable fuel tanks. Volumes and Levels. Publication No Revised FIGURE 2. VOLUMES* (GALLONS)

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1 HEATEC TEC-NOTE SCOPE This document applies to portable fuel tanks currently manufactured by Heatec (Figure 1). It defines different types of tank volumes and enables users to convert levels to volume. VOLUME This is the amount of space available for use. Most of the space inside a fuel tank is used to store liquid fuel. Some of the space is reserved for expansion and overflow control. It is helpful to call different spaces by names that indicate their use. These names and definitions are presented below and shown in Figure 2. In this document, volume is expressed in gallons. This is the most common unit of measure used for storage of fuel at HMA plants in the U.S. NOMINAL VOLUME This is the approximate capacity of a fuel tank. This amount is usually a number rounded off in thousands of gallons. It is useful in classifying tank sizes, but is not an exact indication of how much fuel can be stored in a tank. GROSS VOLUME This is the total amount of space inside a fuel tank. It includes the amount of space reserved for expansion and overflow control. Therefore, gross volume is usually more than the amount of fuel that will be stored in the tank. NET VOLUME This is the maximum amount of fuel that can be be stored in a fuel tank with allowance for expansion. It is equal to the gross volume less the space for expansion and overflow control. It ignores other components such as vent/overflow piping, fill piping, internal fuel preheaters and mixer impellers because the space they occupy is not usually significant. Portable fuel tanks Volumes and Levels RESERVED SPACE This is empty space in the top of the tank reserved for overflow control. It also allows for thermal expansion of the fuel. This space normally extends downward several Figure 1. Heatec portable fuel tank. Revised FIGURE 2. VOLUMES* (S) PORTABLE FUEL S WITH SINGLE WALLS Nominal volume 10,000 Gross Volume 10,445 15,627 20,809 25,991 Reserved space volume** Net volume 10,263 15,355 20,447 25,539 PORTABLE FUEL S WITH DOUBLE WALLS Nominal volume 10,000 Gross Volume 10,649 16,524 22,399 28,274 Reserved space volume** Net volume 10,450 16,215 21,980 27,745 *The volumes shown here apply only to the current line of Heatec tanks. ** Equal to 6 inches from the crest of the tank. inches below the inside crest of the tank. This space varies. It is not included in net volumes shown in Figure 2.

2 Optional overflow controls set off an alarm when the fuel reaches a specified level. The alarm is usually a horn or a flashing light. On some tanks the control shuts off the fuel unloading pump. The amount of space reserved for overflow control depends on the devices used and how they are set up. On some tanks, overflow control is achieved using a float switch. On other tanks, overflow control employs a pressure transmitter and a Honeywell controller. The controller is set to alarm when the level is several inches from the crest, usually 6 inches. The reserved space in your tank may be different from the amount of space shown in Figure 2. 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 alarm is triggered. Then measure the vertical distance from the tank inside crest to the surface of the fuel. This is the amount of reserved space for your tank. CONVERTING LEVELS TO VOLUMES Figures 6 and 7 convert levels to volume or gallons of fuel thereby indicating how much fuel is stored in the tank. Figure 6 is for single-wall tanks. Figure 7 is for double-wall tanks. The internal dimensions of single-wall tanks differ from those of double-wall tanks as shown in Figure 4. It is important to understand that the levels shown in Figures 6 and 7 refer to the height of the liquid above the inside bottom of the tank. You should also be aware that levels indicated by a pressure transmitter is the height of the liquid above the transmitter not the bottom of the tank. The transmitter indicates zero when the fuel level is the same height as the transmitter. The transmitter is normally located 6 inches above the bottom of the tank. Thus, you must add 6 inches to the level indicated by the pressure transmitter to know the level above the bottom of the tank. Do not confuse the levels above the bottom of the tank with levels found by extending a measuring tape through the manway at the top of the tank until it touches the fuel. That is a measure of empty space in the top of the tank not how much fuel is in the tank. However, you can use your measuring tape or stick measurement of empty space to determine the amount of fuel in your tank (see Figure 3). To do so, subtract your measurement from the inside diameter of the tank. (All current portable tanks with single walls have an inside diameter of 126 inches. All current portable tanks with double walls have an inside diameter of 120 inches.) This will give you the level of the fuel above the bottom of the tank. You can now use this level with Figures 6 and 7 to determine the gallons of fuel stored in your tank. Note: When making your measurement it is difficult to measure directly from the inside top surface of the tank to the fuel surface. It is much easier to measure from the bottom edge of the manway to the surface of the fuel. If you do that, you will need to make a separate measurement to determine MANWAY FUEL SURFACE EMPTY SPACE (A PLUS B) FUEL LEVEL (ID MINUS EMPTY SPACE) ID OF SINGLE-WALL IS 126 ID OF DOUBLE WALL IS 120 Figure 3. Making measurements from manway. the distance from the edge of the manway to the topmost surface inside the tank. Then add the two measurements together. Figures 6 and 7 apply to various sizes of Heatec portable tanks. For your convenience, the first three columns show 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. Some people prefer to work with feet and inches, so the third column will eliminate the need to convert inches to feet and inches. Levels shown on the pressure transmitter and on the Honeywell controller are in feet and tenths of a foot, so the second column will be more convenient for readings from these devices. Note: Unlike vertical tanks, volumes in portable tanks are not in direct proportion to the levels. The volume increases or decreases at different rates for each change in level. REFILL VOLUME This is the amount of fuel you can add to a partially filled tank. It is the difference between the net volume (Figure 2) and the volume currently in the tank. It is also an indication of how many gallons have been used since the tank was last filled. This assumes that the net volume is accurate as discussed earlier. Moreover, it assumes that you are not actually using fuel from the tank while it is being refilled. The best way to verify how many gallons a supply truck has added to refill your tank is to record the levels before and after refilling. Then convert the two levels to gallons according to Figures 6 and 7. The difference between the two indicates how much the supply truck added. Again, you cannot make an accurate determination if you are using fuel from the tank at the same time it is being filled. A B ID Page 2

3 ACCURACY Some errors are unavoidable when measuring levels and converting them to gallons of fuel in the tank. Several factors affect the accuracy of determining exactly how many gallons of fuel are in your tank. One factor is the amount of error in the level measurement. Another is manufacturing tolerances related to tank dimensions. Level measurements are made several ways. One way is to simply use a measuring tape. Another way is by installing a pressure transmitter and Honeywell controller. Mechanical clock style gauges with floats are sometimes installed. In any case measurements may have errors of an inch or so. Converting less-than-perfect level measurements to gallons provides a reasonably accurate, but un-verified, number of gallons. The actual dimensions of your tank may vary from its design diameter and length due to manufacturing tolerances. Portable tanks are currently designed with an inside diameter of 126 inches (120 inches for double wall tanks) and the lengths listed in Figure 4. These are the dimensions used to calculate the gallons shown in Figures 6 and 7. Variances in diameter and length due to normal manufacturing tolerances may cause the actual number of gallons to differ slightly from the number of gallons shown in Figures 6 and 7 for a specific level. In the past not all Heatec portable tanks were designed with the dimensions mentioned above. If your tank was designed with different dimensions, you should not attempt to use Figures 6 and 7. The gallons shown in these figures will be significantly different than your actual gallons. In that case, please contact Heatec for a custom-made levels vs. volume table applicable to your tank. CHECKING YOUR PRESSURE TRANSMITTER You should periodically verify the accuracy of the levels indicated by your pressure transmitter. The usual way of checking that your pressure transmitter is accurate is with a measuring tape. As explained earlier, measure the distance from the inside top of the tank to the surface of the fuel. Then subtract this distance from the inside diameter of the tank (126 or 120 inches as applicable). Subtract 0.5 feet or 6 inches from the level indication shown on the transmitter. The resulting numbers should closely agree. FIGURE 4. INSIDE DIMENSIONS PORTABLE S WITH SINGLE WALLS Nominal volume (gallons) 10,000 Length (inches) Diameter (inches) PORTABLE S WITH DOUBLE WALLS Nominal volume (gallons) 10,000 Length (inches) Diameter (inches) *The dimensions shown here apply only to the current line of Heatec tanks. EFFECTS OF TEMPERATURE The information in this document is based on fuel at a temperature of 60 degrees F. The volume of fuel in your tank will change when the fuel expands or contracts as a result of temperature variations. Temperature of the fuel will vary with the ambient temperature. Its temperature can also change if a fuel pre-heater is used and heated fuel is returned to the tank. You should make allowances for changes in volume due to temperature, especially when filling the tank. Figure 2 shows the net volume for Heatec fuel tanks with an allowance of 6 inches of reserve space for expansion and an extra margin of safety. Most ambient temperature fluctuations during a 24 hour period will have very little effect on a full tank of fuel. The temperature of the fuel will probably remain close to an average of the ambient temperatures over 24 hours. However, fuel temperatures are apt to change to a greater extent over several weeks or months, when the weather changes from one season to another. Figure 5 shows how changes in fuel temperature affect its volume. The volumes shown for 60 degrees F correspond to the capacities of standard Heatec tanks. The temperatures should be regarded as average temperatures over a period of 24 hours. Figure 5. How fuel volumes (gallons) vary with temperature 30 Deg F 40 Deg F 50 Deg F 60 Deg F 70 Deg F 80 Deg F 90 Deg F 100 Deg F , , , , Heatec, Inc Wilson Road Chattanooga, Tennessee (423) (800) Fax (423) Heatec, Inc. Page 3

4 FIGURE 6. SINGLE WALL S LEVELS VS. GROSS VOLUMES (S) (PART 1 OF 3 PARTS) Feet/ Feet/ Tenths Page

5 FIGURE 6. SINGLE WALL S LEVELS VS. GROSS VOLUMES (S) (PART 2 OF 3 PARTS) Feet/ Feet/ Tenths Page

6 FIGURE 6. SINGLE WALL S LEVELS VS. GROSS VOLUMES (S) (PART 3 OF 3 PARTS) Feet/ Feet/ Tenths Page

7 FIGURE 7. DOUBLE WALL S LEVELS VS. GROSS VOLUMES (S) (PART 1 OF 3 PARTS) Feet/ Feet/ Tenths Page 7

8 FIGURE 7. DOUBLE WALL S LEVELS VS. GROSS VOLUMES (S) (PART 2 OF 3 PARTS) Feet/ Feet/ Tenths Page 8

9 FIGURE 7. DOUBLE WALL S LEVELS VS. GROSS VOLUMES (S) (PART 3 OF 3 PARTS) Feet/ Feet/ Tenths Page 9