2. Mark this center peg at a point 6 inches from the top) and drive it down in the grade to this mark.

3. Use a wooden straightedge with a carpenter's level attached to set grade stakes about 10 feet apart. Note that, set in this manner, they will protrude 6 inches above the earthen grade.

4. Distribute sand over the whole grade, using shovels and rakes. When the sand just covers the top of each of the stakes and the center peg, the proper level has been reached.

5. Drive the stakes and the center peg all the way down into the earth under the sand. When the tank is filled, the sand will compact, and if the stakes are not driven down, they may cause leaks. Mark the position of the center peg with a temporary pin so that you will be able to position the center of the tank bottom later.

6. To make the surface smooth, use a sweep with a carpenter's level attached. Pin the sweep to the center peg and drag it over the sand, filling in any hollows and smoothing out humps. The sand pad should be at least 4 inches thick and should have a crown of about 1 inch in 10 feet of tank radius; however, the crown should not exceed 6 inches.

When a foundation is properly prepared, many unnecessary problems do not occur during construction of the tank. Just imagine the problems that might occur, both in erection and in subsequent maintenance of a tank, if the foundation were to settle unevenly, throwing the steel plates on one side of the tank slightly out of line. Remember that the walls of the tank-consisting merely of steel plates bolted together-must act as bearing walls to support the roof. So, make sure you have a good foundation before starting to assemble a tank.

in the tank bottom. The vertical seams have one row of bolt holes.

Figure 9-1.-100-barrel capacity, vertical, bolted steel tank.

BOLTED STEEL TANK ASSEMBLIES

Tanks are assembled by sections, consisting of pieces of various sizes and shapes that combine to form cylindrical structures. Among the most common are the bolted steel tanks, having a capacity of 100, 250, or 500 barrels of liquid Many tank sections serve the same function regardless of tank capacity. However, the number of sections used in each assembly will vary according to capacity. The procedures for assembling and erecting these tanks are similar.

100-Barrel Tank

The 100-barrel tank shown in figure 9-1 is the smallest bolted steel tank. It has a holding capacity of 4,200 gallons of liquid and is made up of preformed and punched metal sections, fastened together with l/2-inch-diameter bolts. The tank bottom (fig. 9-2) consists of two semicircular halves, bolted together at a lap joint along the center of the tank bottom. This vertical, bolted steel tank has a 9 foot 2 3/4-inch-inside diameter and is 8 feet 1/2 inch high at the sidewall.

SIDE STAVES.-The side staves consist of six curved, vertical sections, arranged in a single ring. The staves are chimed (flanged) at the top and bottom of each section with the left end of each chime offset so the vertical seams overlap. The bottom chime bolt holes are patterned to match the outer edge bolt holes.

Figure 9-2.-Tank bottom.