CHAPTER 3 - Pressurisation of Sealed Systems

Abstract

This chapter discusses the concept of pressurization of sealed systems. It discusses steam cushion in steam boiler, steam cushion and hot water boiler, pressurization by compressed air, and pump pressurization. Steam cushion in steam boiler is one of the original forms of high pressure hot water generation, its initiation dating back to 1923. It was used for many installations in the past and applied to most practiced design temperatures 130°C–180°C. The system features a high pressure steam boiler as hot water generator, whereby steam pressure is developed in accordance with desired water temperature and steam, thus, generated within the steam space of the boiler acts as cushion containing the expanding system water. Development of hot water generation using hot water boilers pressurized by own steam cushion created in a directly connected high level closed expansion header vessel was initiated around 1945, consequent upon functional and operational problems associated with the systems using the steam cushion and expansion space within steam boiler units. The aim was to create a safe and reliable, if possibly more expensive system, independent of critical conditions caused by direct interdependence of pressure and temperature of generation in steam boilers, and ensuring the least functional disturbance in case of emergencies resulting from the failures of combustion or of circulating pumps.