Frequently Asked Questions - Tanks
Is the U.L. approved paint okay for inside of my potable water tank?
The Rust-Oleum W9200 Potable Water Epoxy paint is certified by Underwriters Laboratories for use in potable water tanks over 1,000 gallon minimum in accordance with ANSI/NSF Standard 61. Underwriters Laboratories is an approved lab for testing and certifying products for compliance with this standard. USA BlueBook recommends that you check with your local regulatory agency for their approval before purchasing this product.
What applications are not suitable for linear polyethylene tanks?
| • | Holding liquids with temperatures in excess of 150 degrees Fahrenheit. |
| • | Exposure to liquids such as aromatic hydrocarbons (gasoline, diesel fuel) and halogenated solvents (carbon tetrachloride) |
| • | Mixed use, using tank for alternately holding non-compatible chemicals (eg. sodium hydroxide and sulfuric acid) |
| • | Pressurized tank applications (designed for atmospheric use only). |
Do all polyethylene tanks meet NSF Standard 61 for potable water use?
| No. To meet NSF Standard 61, the tank manufacturer must have their products tested and approved by NSF as meeting or exceeding Standard 61 criteria. NSF Standard 61 states that tanks must not leach potential contaminants from the resins used in manufacturing the tank into the stored liquid, or that any leaching that does occur must not exceed acceptable public health levels. | ||||||
| However, NSF Standard 61 is relatively new. Linear polyethylene tanks without NSF Standard 61 approval have been used to store potable water for years. The materials used in manufacturing these tanks comply with the U.S. Food and Drug Administration Regulation 117.1520. The criteria used in Regulation 117.1520 is very similar to that used in NSF Standard 61. Some states are now specifying that tanks must meet the actual NSF Standard 61 for potable water storage. Before purchasing a tank used for potable water storage, verify with your local regulatory agency which standard/regulation is accepted in your area. | ||||||
| In addition, please note the following: | ||||||
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How heavy of a material can I store in a polyethylene tank?
A tank with a specific gravity of 1.5 can hold a liquid up to 12.5 pounds per gallon at 100 degrees F. A tank with a specific gravity of 1.9 can hold a liquid up to 15.75 pounds per gallon at 73 degrees F. Please note that an increase in liquid temperature will substantially decrease the specific gravity rating. Also, certain chemicals have environmental stress cracking agents in them so higher specific gravity tanks are needed to compensate even though the weight of the chemical may be lower.
What is the maximum temperature that your tanks will withstand?
Linear polyethylene (HDLPE) storage tanks have a maximum storage temperature of 130 degrees F. Cross-linked polyethylene (XLPE) storage tanks have a maximum storage temperature of 140 degrees F.
I need to provide containment for my solution tank. How do I select the proper containment basin for my tank?
To select a proper containment basin, the basin should be 10% greater than the largest tank in containment.
If I order a horizontal tank, do I need bands with that tank? Why?
Yes, because they keep the form of the tank. Over time the weight of the solution in the tank tend to bulge the outer side walls of the tank.
Why do I need a flexible connector?
During filling and emptying, a polyethylene tank wall will flex. If the tank is connecting to ridge pipe, it can cause the tank or fittings to fail.
What is a bulkhead fitting?
A bulkhead fitting is a two part fitting that is placed on each side of a hole cut into a tank. There is a gasket between the tank wall and the fitting to prevent leakage. Care should be given to select a gasket that is compatible with the chemical in the tank.
What is a hydro-pneumatic tank used for?
| These tanks store water prior to distribution in a water supply system, working with the pumps to maintain a stable water system pressure. The system pressure is controlled by a pressure switch set for minimum and maximum pressures — giving you a cut-in and a cut-out pressure for the pumps. When the pumps cut-out or stop running, water demand is met by the water volume in the piping and the tank. As water is drawn down, the system pressure starts to drop. When it reaches the minimum system pressure, the pump cuts back in and runs until the system pressure reaches the normal maximum pressure. |
| Any vessel that contains both water and air under pressure can be called a hydropneumatic tank. The two most common applications are in well water systems, or as buffer tanks to absorb water hammer shocks in large capacity pumping systems. In both cases, the captive compressed air acts as a cushion which can exert or absorb pressure as required. |
| Large hydropneumatic tanks are usually horizontal and 2000 gallons or more. The size is determined by the needs of the system, and is approximately the drawdown gallons times four. A small air compressor can be included to replenish the air volume periodically as it is absorbed into the water. Sensors monitor the water level and pressure and automatically control compressor operation as required. These vessels are usually lined to prevent corrosion and have a design working pressure from 100 to 150# ASME. |
| Tanks that include an internal bladder are usually smaller, and sometimes called captive air or bag tanks. There are styles that are designed to replace the expansion tank in a domestic hot water system. All bladder tanks are usually a standard vertical design. On larger versions, the bladder is often replaceable through a flange, which can be either on the top or bottom of the tank depending on the application. |