Chemical storage tanks can be equipped with a number of different fittings and accessories to improve the safety, efficiency, or ease of filling and emptying the tank. One option is a fill line, which is a drop pipe that is affixed to the tank with a support and comes with a ball valve and quick cap to keep the line from transferring chemical when it is not in use. Fill lines are available in internal, external and combination versions. Another option is an anti-foam elbow, used as a substitution for an internal fill line.
About Fill Lines
Fill lines need proper support, whether they are internal, external or a combination. They need to be properly anchored to the tank - a proper support ensures that the line is durable and stable in the event a truck or piece of equipment inadvertently bumps the line. Lines can be made out of PVC or CPVC to ensure chemical compatibility. Let’s take a look at the different types of fill lines and their benefits, and when an anti-foam elbow might be a better choice.
Internal Fill Lines vs. Anti-Foam Elbows
Internal fill lines are supported on the tank’s interior and have a fitting on the top of the tank. The tank’s application and the customer’s specification will dictate what type of fitting is attached to the line, but a universal ball dome is standard. The pipe itself is attached to the fitting with a coupling, and the pipe reaches down into the tank almost to the bottom. The standard length is two inches from the tank’s bottom, although this can be adjusted according to the customer’s specifications. When a tank is filled with an internal fill line, splashing and foaming are reduced or eliminated. These pipes can also act as a means to drain the tank, eliminating the need for a sidewall fitting.
The potential drawback to an internal fill line is that, in certain circumstances, it can cause internal tank pressure on filling. The more dense the fluid, the more possibility for hydraulic hammering to occur. This can be caused if pneumatic air pressure pushes air bubbles to bottom of tank which already has several feet of head pressure from a partially filled tank. One alternative is an anti-foam elbow, which is a small elbow assembly that attaches to the top of the tank for filling. It comes down vertically and forms a 45 degree angle toward the sidewall of the tank. Picture pouring a carbonated beverage down the side of the glass instead of directly into it and you’ll see the difference between an internal fill line and an anti-foam elbow. In addition to reducing the pressure caused by an internal fill pipe, the anti-foam elbow is a more cost-effective option because it is a small, singular assembly.
External Fill Lines
Exterior fill lines are affixed to the tank’s sidewall via an external pipe support to provide stability. The pipe is affixed to the top of the tank via a fitting as required, though, like an internal line, the standard is a universal ball dome. There is no internal line that reaches into the tank. The end of the external pipe will be fitted with an elbow and short nipple so that trucks can connect their hoses to the line for easy filling. The line can also be connected to other pipes so that the tank system can extend from an indoor to an outdoor area, or across a warehouse so that access to the tank is more convenient.
Combination Fill Lines
With a combination fill line, you get the best of both worlds. It’s easy to fill the tank with an easy flow to reduce splashing and foaming, it is easy to suction with the drop pipe, just like the internal fill line. You also have the option of connecting to other components or providing access to a hard-to-reach tank like you get with the external fill line. That’s because of the marriage of the internal and external lines. In a combination fill line, a drop pipe extends into the tank almost to the tank bottom, is connected to a fitting (usually a universal ball dome), which is connected to a coupling to which the external pipe is joined. The combination fill line is supported inside and outside of the tank for maximum safety and stability.
Depending on your chemical application and the configuration and placement of your tank system, you may need one fill line rather than the other, or you might consider an anti-foam elbow.