Before the increase in temperature, the pressure inside the vessel balances the installation static pressure. The nitrogen fills the whole vessel volume. The diaphragm remains stuck against the wall.
During the increase in temperature, the water volume in the system increases under the effect of expansion and compresses the diaphragm. The nitrogen volume decreases and the pressure in the installation increases. After the increase in temperature, the final pressure nears the calibration pressure of the safety valve.
When the boiler is shut down, the water in the system cools down and the installation pressure decreases. The water contained in the vessel returns to the system to restore the pressure and the water volume
In cooling and air-conditioning installations: • when the system cools down, the water volume decreases; the expansion vessel returns the water to the system to maintain the pressure. • upon shutdown, the water at ambient temperature expands, the increased volume of water enters the vessel and compresses the diaphragm.
• Direct pressure boosting A small vessel maintains the pressure in the installation when no delivery is required and protects the pressure controller against pressure variations and water expansion.
•Conventional pressure boosting A large vessel with a large useful water reserve covers the low deliveries required by the installation.
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