HBG model high back pressure foam generators are used to expand foam solution even under counter pressure conditions i.e., increased length of discharge piping at downstream or liquid mass stored inside the tank when used with SSI semi sub surface injection systems to discharge expanded foam onto the liquid surface stored in the tank from low levels. These systems can only be used with fixed roof storage tanks and are not recommended to be used with floating or internal floating roof tanks. The sub-surface method should only be used on tanks containing standard hydrocarbon-based fuels such as: diesel, kerosene, gasoline, etc. It is not suitable for use on tanks that contain alcohol or polar solvent type liquids that are miscible in water. HBGs are equipment like Venturi inline mixers, used to aspirate air and mix it into the solution flow to create a forced expansion in the equipment. HBGs can handle a counter pressure up to 40% of the pressure entering the equipment. HBGs are supplied with factory calibrated primer orifice and Venturi combination to guarantee a precise flow rate at the desired pressure. The air suction port is equipped with a swing type check valve, to avoid foam solution loss caused by poor inlet pressure and it guarantees complete rupture of the separation discs at the discharge port of the HBGs. Carbon Steel and Stainless-Steel materials are available on request.