Expansion tanks are among the most critical auxiliary equipment in heating systems. Essentially, materials referred to as expansion tanks manage pressure control and provide water support. Categorized as a type of “installation equipment,” these products ensure high efficiency in heating systems. Depending on their capacity, operating principles, or models, there are different types of expansion tanks. They operate under very high temperature ranges, making them essential for areas such as heating or sanitary water installations.
Expansion tanks precisely control the expansion of water that occurs when the water in the system heats up. Water begins to expand significantly due to temperature, causing pressure to rise in heating systems. As pressure increases, it can damage the system, making pressure control critical. Otherwise, it becomes impossible to achieve efficiency in heating systems. Expansion tanks can function across a wide range of capacities, such as 50 liters or 500 liters.
Features of Closed Expansion Tanks
Closed expansion tanks, which hold a special place among expansion tanks, are extremely attractive in terms of lifespan and durability. Due to certain placement issues experienced with open expansion tanks, the popularity of closed expansion tanks has significantly increased in recent years. These products are fully compatible with membranes. In closed expansion tanks, water is contained directly inside the membrane and does not come into contact with the tank. For this reason, closed expansion tanks are used in heating, cooling, and sanitary water processes. When selecting closed expansion tanks, it is ideal to act according to capacity. For example, vertical-legged models may be preferable for a 200-liter tank, while smaller tanks are better suited for spherical, legless models.
The dimensions of closed expansion tanks may vary depending on their models. Similarly, their prices may differ based on size and performance potential. Choosing according to the usage area and needs is crucial for cost management. Closed expansion tanks prevent issues caused by excessive pressure in heating systems, improve system efficiency, and prevent potential breakdowns. Thanks to these benefits, closed expansion tanks attract considerable interest. Today, they are actively used in many areas, from washing systems to water and pressure systems.
The most well-known technical feature of closed expansion tanks is that the system water does not come into contact with the steel tank. Additionally, the membranes in these tanks are bellows-type. Tanks are coated with electrostatic powder paint. Nitrogen is used to provide the initial gas pressure in closed expansion tanks. During pressure adjustment, air can be used instead of nitrogen.
Maintenance of Closed Expansion Tanks
Periodic maintenance of closed expansion tanks should not be neglected and must be performed at regular intervals, as routine problems may occur due to air loss. On average, routine maintenance should be done every 2–3 months. This significantly increases the lifespan of the tank. Another maintenance issue is leakage. If there is no air in the closed expansion tank, water begins to accumulate, which may eventually lead to water leakage. Once the tank is punctured, it cannot be repaired; replacement is the only option, which can be costly.
Closed expansion tanks are a standard component not only in heating systems but also in booster pump installations, which contributes to their popularity. They are designed with diaphragm membranes and are used exclusively in closed-loop heating systems. Balloon-membrane closed expansion tanks are also available, in which water never touches the steel tank and always remains inside the membrane. A properly selected closed expansion tank prevents sudden pressure changes, significantly extending the lifespan of the pump.
Closed expansion tanks also prevent heat loss in pipes, ensure more balanced heating of radiators, reduce labor costs, and minimize corrosion.
Calculation Processes for Closed Expansion Tanks
Closed expansion tanks are notable not only for their benefits but also for their superior performance and efficiency. These tanks are highly sensitive equipment, so calculations must be approached carefully. Several criteria must be considered when calculating a closed expansion tank.
It is important to note that expansion tanks vary in size depending on the characteristics of the pump systems, ranging from 2 liters to 5,000 liters. Tanks can be horizontal, vertical, or spherical. Before calculation, the height of the installation area is a crucial factor, as it affects the tank’s resistance to pressure. In humid environments, stainless steel tanks should be preferred. Key parameters in calculations include pressure class, initial gas pressure, and volume. Pressure class and volume calculations require separate formulas. For example, water volume can be calculated using the formula:
Vs = Q × f
Where Vs represents the total water volume in the system in liters, and Vg represents the expanding water volume. O is the nominal heating level of the boiler, and f represents the heat emission force of the heaters. The volume of expanding water is calculated using:
Vg = Vs × n
Closed expansion tanks are vital for protecting the system. During peak periods when the tank is insufficient, a certain amount of water can be discharged to reduce system pressure. The tank compensates for volumetric changes in heating water, balancing flow variations.
In heating systems or certain installations, a well-chosen and properly calculated closed expansion tank ensures the longevity of other system components, including pumps. Closed systems also reduce corrosion by eliminating air contact and prevent water loss. Heat losses in pipes are significantly reduced with closed expansion tanks.
To calculate closed expansion tanks, the total water volume must first be determined, including water in boilers, heaters, and pipes. This information can also be obtained from manufacturers’ catalogs.
For tank volume calculation, the following formula is used:
Vgd,k = Vd + Vs × E × [(Ptü + 1) / (Ptü – Pgö)]
Where:
Vgd: Tank volume in liters
Vs: Water volume in the installation
E: Water expansion ratio
Ptü: Maximum operating pressure of the system
Pgö: Initial pressure of the tank
Vd: Water level in the tank when the system is cold
For nominal tank volume:
Vn = Vv + Ve
Accurate calculation of these parameters ensures smooth operation of the expansion tank.
During calculation, the operating pressure of components such as valves, radiators, and pumps must be at least 10% higher than the safety valve opening pressure. Minor water loss may occur initially due to trapped air, leakage, or small gaps.
In some European countries, solutions like pressure switches or solenoid valves are used to prevent water loss, but these are considered risky in Turkey due to frequent sudden water cuts in large cities.
The expanding water volume in the system can be calculated as:
Ve = n × Va / 100
Where Va is the water volume in the system, and n is the temperature-proportional expansion coefficient. The initial pressure of the closed expansion tank should be:
Po = Ps + Pd
Where Ps reflects static pressure, and Pd represents the effective pressure of water vapor.
There are two classical methods for calculating expansion tanks. The first involves calculating water levels in pipes or devices and multiplying by the expansion coefficient. The second estimates system needs and applies a safety factor. The first method is more precise for large systems, while the second is simpler for smaller ones.
Water level calculations, fixed-pressure and safety valve calculations, normal water volume, and normal expansion tank volume are all calculated using separate formulas. Closed expansion tank calculations must be performed professionally for accurate results.