Two-pass or three-pass hot water boilers are fully cylindrical, high-efficiency systems featuring a fire-tube (flame-smoke tube) design and substantial water volume capacity. Engineered for liquid fuels, these boilers are designed to burn Fuel Oil (No. 4 and No. 6) and Diesel with peak thermal performance.

In these installations, the burner is initially ignited using diesel. Once the hot water system reaches a specified operating pressure, the diesel feed can be deactivated, allowing the system to transition to fuel oil combustion.

The fuel storage infrastructure, comprising the main and daily fuel tanks, utilizes steam-heated serpentine coils. The fuel oil is preheated using steam generated during the initial diesel-firing phase. Once the fuel reaches an optimal temperature of 80°C, it is delivered to the burner via precision gear pumps to facilitate combustion.

The liquid fuel delivery system incorporates critical components such as the main storage tank, daily service tank, diesel tank, fuel heat exchangers, and a pot tank. This configuration ensures that the fuel reaches the burner at the required viscosity. Any unburned fuel is circulated back to the heating exchangers through a dedicated return line to maintain thermal consistency.