What is expansion tank for boiler?
Expansion tank for boiler, is a kind of
expansion tank when the water loss pressure is reduced when the gas pressure inside the expansion tank is greater than the pressure of the water, then the gas expansion will be the water inside the gas bag extrusion to the system.
Expansion tank is widely used in central air conditioning, boilers, water heaters, variable frequency, constant pressure water supply equipment, its buffer system pressure fluctuations, eliminate water hammer to play the role of pressure stabilization and unloading, in the system when the water pressure changes slightly, the automatic expansion contraction of the expansion tank air bag will have a certain buffer effect on the change in water pressure, to ensure that the system's water pressure stability, the pump will not change due to the pressure and frequent opening. As the name implies, different from the traditional diaphragm type expansion tank, air bag type expansion tank in the body of the tank with an air bag.
Working principle of expansion tank for boiler
When the external pressure of water into the expansion tank gas bag, sealed in the tank of nitrogen gas is compressed. According to Boyle's gas law, the gas is compressed by the volume becomes smaller pressure increases, until the expansion tank gas pressure and water pressure to reach the same time to stop the water. When the water loss pressure decreases, the gas pressure inside the expansion tank is greater than the water pressure, then the gas expansion will be the water inside the gas bag to squeeze out to the system.
When the boiler system expansion tank is used in the system, because the system pressure than the pressure of the pre-charged gas, so there will be part of the working medium into the bladder (for the diaphragm type is into the tank body) until a new equilibrium is reached. When the system pressure rises again, the system pressure is again greater than the pressure of the pre-charged gas, and some of the medium will enter the bladder, compressing the gas between the bladder and the tank, and the gas is compressed and the pressure rises. When the pressure rises to the same level as the system pressure, the medium stops entering; conversely, when the system pressure falls, the medium pressure in the system is lower than the gas pressure between the capsule and the tank, the water inside the capsule will be squeezed out by the gas to replenish the system, so that the system pressure rises until the system working medium pressure is equal to the gas pressure between the capsule and the tank, and the water inside the capsule is no longer replenished outside the system to maintain the dynamic balance.
Type of expansion tank for boiler
Expansion vessel boiler is divided into two types of air bag type and diaphragm type.
Diaphragm type pressure tank
Diaphragm type pressure tank completely realize the separation of gas and water, water on one side of the rubber diaphragm, the other side is pre-filled with air, this pressure tank does not have the problem of gas soluble and water loss, can be inflated once, long-term use. Therefore, save investment, simplify the system, expand the scope of use, commonly used in high-rise secondary water supply.
Diaphragm type expansion tank shell is in direct contact with water, the shell are sprayed rust-proof layer. The tank is welded between the interface and the shell. During the welding process, the high temperature will oxidize the anti-rust coating. The original silver-white coating appears black after welding. Small black particles can be felt when touched by hand. These seemingly insignificant oxidation points work for a long time in contact with water, slowly rust and gradually expand, until the corrosion of the entire tank.
Diaphragm expansion tank membrane is fixed in the middle of the carbon steel of the two half shells of the expansion tank by hot rolling, this process if not handled well, will leave tiny pores between the membrane and carbon steel, these tiny pores will be pre-charged gas leaks out, expansion tank if leaking gas, 90% is leaking from here. This leaky expansion tank with a period of time if not timely replenishment of gas will not be able to play a fixed pressure unloading role. In addition, due to the expansion tank wall thickness is generally about 1mm, the interface directly welded together with the tank, this coupling can withstand the torque is quite small. The installation of the tank can only hold the shell rotation, if too much force or too hard, the interface will be spun off. This situation is most common in the production process of air conditioning.
Boiler expansion tank full of water
Airbag pressure tank gas and water separate, water in the rubber bladder inside, the gap between the outside and the tank pre-filled with air, this pressure tank no gas and water loss problems, can be once inflated, long-term use (requires regular maintenance).
The airbag type expansion tank has an integral airbag inside, and the water only enters the airbag when working, not in contact with the shell. The interface is connected with a flange. This structure avoids the rusting problem caused by the welding process. In addition, the air bladder of this structure of the expansion tank can be replaced. Likewise, because it is flanged connection, so its interface will be able to withstand a large torsional force, and there is no fear that the interface will be twisted during installation.
Application of expansion tank for boiler
Expansion tank is used in thermal systems (boilers, air conditioners, heat pumps, water heaters, etc.), is mainly used to absorb the working medium due to temperature changes in that part of the volume; expansion tank applied to the water supply system is mainly used to absorb the system due to valves, pumps and other open and closed caused by water hammer impact, as well as a small amount of water replenishment at night, so that the main pump of the water supply system dormant so as to reduce electricity consumption and extend the life of the pump.
Installation of expansion tank for boiler
a. Expansion tank in thermal systems such as air conditioners, boilers, heat pumps, etc. are generally installed in the return end of the system.
b. Expansion tank in the water supply system is generally installed at the outlet of the pump.
c. Expansion tanks are generally installed near the inlet of the pump in solar pressure-bearing circulation systems.
d. It is recommended to install in the system water temperature relatively low point of the return end or the cold water into the end of the hot water storage tank. 24L or less can be directly connected to the system piping. Avoid the expansion tank in the work of the water and self-weight on the system piping to produce a large load, more than 24L expansion tank with its own triangular bracket, you can use a metal hose to connect the expansion tank to the system, buried screws fixed expansion tube legs, to ensure the smooth use of the process.
Use of expansion tank for boiler
a. If the expansion tank is placed in a special occasion, the supplier should be informed so that there is a relevant membrane body corresponding to the use.
b. Expansion tank work medium is generally water or a mixture of water and antifreeze (the proportion of water should not be less than 50%), other media need to consult professionals after use.
c. Strictly according to the formula to calculate the size of the required expansion tank. The expansion tank is too small to cause frequent tripping of the safety valve and frequent replenishment of the automatic replenishment valve.
d. The maximum working pressure of the expansion tank corresponds to the pre-charge pressure marked on the tank, if the pre-charge pressure is changed due to the use of the need, the maximum working pressure will change, basically following the rule below, the pre-charge pressure decreases, the maximum working pressure decreases, the specific reduction to how much to calculate, the pre-charge pressure increases the maximum working pressure remains unchanged.
e. It is recommended to test the expansion tank air bag directly with water pressure test, it is strictly prohibited to use sharp devices to touch the air bag.
f. Expansion tank should be checked once a year for its pre-charge pressure, if found that the pressure drop should be timely replenishment of gas, so as not to affect its normal use.
g. The working temperature and maximum working pressure are indicated on the label of the tank, it is strictly forbidden to use beyond this range, if necessary, please contact the manufacturer.
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