Blue Duda Solar Expansion tanks are constructed with a food grade EPDM diaphragm for potable water applications. These should be used for relieving pressure from building up in the domestic water tank as it heats from the solar loop. Use of an expansion tank helps regulate the pressure so that it does not get too high in the tank and cause water loss due to the T/P valve opening when the pressure of the water exceeds the limit.

Wattspotable Water Expansion tank

The difference in water density from cold (4°C) to near boiling (99°C) is approximately 4%. For maximum expansion capabilities, your expansion tank capacity should be 4% the size of your water heater. ie: A 300 liter tank should have a 12L expansion tank.

Potable water expansion tankpurpose

Note that the expansion tank will have an air charge in it which determines when the expansion tank should start relieving pressure. For this reason, not all of the tank's capacity will be available as some of it will be filled with air. For best results, choose a size 1 model larger than what you need.

Potable water expansion tankleaking

The size of the expansion tank needed depends on the total amount of fluid used in the closed loop (maximum possible volume). Some data regarding common fluid volumes in the solar systems is in the chart below.

Expansion tanks are also very useful in well pump applications. In order to avoid the pump turning off and on constantly, an expansion tank of adequate size should be placed in line to receive a hold water. When the tap is opened, the expansion tank will push out water using the pressure created by the air inside of it. The well pump will only need to turn back on when most of the expansion tank is empty and the water pressure has dropped below the minimum pressure threshold.

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Potable water expansion tankinstallation

Expansion tanks are essential for solar water heater systems. The Red expansion tank is used for relieving pressure build-up in the closed loop system. This helps keep the pressure consistent and relieve pressure from the piping as the working fluid increases in temperature. Should the solar system go into overheat mode and shut down the circulation pump, the expansion tank is essential for preventing the pressure valve from blowing out the working fluid. The Red Duda Solar expansion tank is fitted with a special high temperature EPDM membrane made in Italy which can withstand the high temperatures of the solar systems.

As an example, a standard 300 liter solar system has a 30 tube collector, 100 feet of 1/2" stainless steel tubing and a 300 liter tank (25m coil) for a total of ~7 liters of fluid volume, requiring at least an 8 Liter expansion tank.

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Duda Solar expansion tanks come pre-charged with some air from the manufacturer. This charge can be increased or decreased with a typical inflation valve. This air charge should match the pressure at which you want the working fluid to begin entering into the expansion tank (usually just above the normal working pressure). As fluid pressure increases, some fluid enters into the tank, pushing the air back and thus rising the pressure of the air. Eventually, the tank will become nearly full with fluid or reach the maximum working pressure for both the fluid/air. For system and tank protection, a safety valve must be installed in addition to the expansion tank.

Each expansion tank comes with a galvanized flange. For most applications, the galvanized flange is adequate. However, if your enviornment is prone to higher rates of corrosion, or if you intend to connect metal piping to the expansion tank which may accelerate the corrosion process, stainless steel flanges are available which can be swapped with the galvanized flange.