The pressure vessel is used to provide a reserve of pressurised water to limit the number of starts of, and wear on, the pump. The pressure switch will cut in when the pressure drops below a preset point starting the pump and cuts out when the required pressure is achieved.
Pressure vessels are most often used in domestic waterworks applications. Their main function is to balance and maintain a constant pressure in the water distribution system. They serve as water tanks and protect your pump from frequent switching, which could lead to rapid wear. Pressure vessels are most often made of steel and can be purchased in various sizes and volumes.
There are two types of pressure vessels - horizontal and vertical. Due to the size, large tanks are constructed with legs, which prevents the installation of horizontal containers (for example) in a vertical position. Installation other than the recommended may result in damage to the tank and loss of functionality. They are designed to apply pressure from top to bottom, so that if the installation is inverted, the pressure will be applied in a different direction than for which it was designed, and your vessel will be damaged.