High Pressure Natural Circulation Steam Boiler The NUK-HP® is a high-pressure natural circulation boiler operating by the gravity circulation principle. Therefore circulating pumps are not required to operate the NUK-HP®. Boiler water is used as the heat carrier. The water is evaporated in this boiler within a hermetically sealed circuit. The steam flows to the heat exchanger and the condensate flows by gravity back to the boiler.	Application/Advantages Production/Equipment Technical Data P+I Diagram/Schema