Expansion vessel TerNWP

TerNWP – Expansion vessel for central heating system


Designed as a heating water system protection against excessive pressure due to change in medium temperature. Using the expansion vessels instead of the open tanks allows to cut off the air access and reduce system susceptibility to corrosion. Installed in the highest system point.


  • compensation of pressure increase due to temperature increase
  • compact design
  • replaceable diaphragm


The expansion vessel is designed as a cylindrical steel tank (1) with a rubber diaphragm (2). The diaphragm is connected to the water system with G1¼” port in the bottom cover (4).  The expansion tank is vented with an automatic air vent (10) installed in the top cover (3). The tank shell is fitted with a pressure gauge (5) and pneumatic valve (6) for filling the gas chamber. The bottom heat is fitted with a port (7) for checking diaphragm integrity. Compact design allows to install large capacity vessels in rooms with standard door openings. The expansion vessels can be dismantled to replace the diaphragm (2).

 Principle of operation

Chamber (A) is connected to the water system via G1¼” port. Chamber (B) is filled with gas to initial pressure of 3 or 5 bar. If the medium volume in the system increases due to increase in temperature, the diaphragm is filled with water in direct proportion to the increased volume. The system pressure increases to the value corresponding to the increase in gas pressure in chamber (B) corresponding to the reduction in gas chamber volume. By releasing or adding air with a pneumatic valve (6) the initial working pressure is adapted to the system requirements. The pressure in the gas chamber can be read on a pressure gauge (5). Chamber (A) is vented with an automatic air vent (10) installed on the top cover (3).


TerNWP vessels are CE marked .

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