Used in the fuel system of ships, KRAL screw spindle pumps with magnetic coupling offer essential advantages. Among them are reduced lifecycle costs and noticeably higher operational safety.

Normally, fuel oils that power ships are diesel fuel or heating oil EL and heavy oil. They have to be prepared in on-board facilities, referred to as fuel modules, where particles are filtered; condensation water is separated and the viscosity of the fuel is conditioned by heating systems.

Safe Feeding Process

The fuels must be conveyed from the storage tanks to the day tanks and further on to the fuel modules from where they are finally fed into the engine’s fuel injection pumps. KRAL screw spindle pumps, conceived as self-priming displacement pumps, can feed oil safely – even from deeper lying tanks. This is very important for allowing any conden-sation water contained in the fuel to be centrifuged in the separators. The behavior of the pumps in varying viscosity is a further advantage when fuel viscosity changes occur due to climate or operations-related temperature fluctuations.

Advantages of Magnetic Coupling Pumps

When a pump fails, it is frequently due to sealing trouble. Conventional pump sealing, such as mechanical seals, have the disadvantage of friction at the sealing area. To re-duce friction, the faces of the mechanical seal rely upon the pumped fluid for lubrication. The pumped fluid comes in contact with the atmosphere as it moves across the sealing faces. The result is often leakage at the seal.

For a long time now, hermetically sealed magnetic coupling pumps only have fixed sealing elements; the actual sealing element is the stationary stainless steel can, installed inside. Operating entirely without friction, the torque is transmitted from the motor to the pump shaft. Magnetic couplings operate practically wear-free so the operational safety of the pump is considerably raised.

In pumps with axial face mechanical seals, the ball bearing must constantly be lubricated with leakage. If the flow of leakage is increased and if the medium reacts with air, it will settle in front of the ball bearing. Consequently, the residue will damage the ball bearing, the elastomer insert will melt and the coupling will get damaged. With the hermetically sealed can of the magnetically coupled pumps, no feeding medium will escape into the atmosphere and the pump area will stay clean.

The heavy fuel oil is generated from oil refinery residuals. In order for the highly viscous fuel – up to 500mm²/s – to obtain a sufficiently low injection viscosity required for burn-ing, they have to be preheated to 180°C. Installed axial face mechanical seals, how-ever, can be damaged at temperatures above 150°C, leading to pump failures and en-gine shut down. Ships become unable to be maneuvered and there is a maximum risk of grounding that may endanger lives and the environment. Where temperatures approach 250°C, KRAL magnetic coupling is the right choice.

Higher Safety at Lower Costs

The lifecycle costs of a pump with magnetic coupling are much lower than that of a pump with conventional sealing. A case of malfunction makes this fact clear: a single seal replacement on a pump with conventional sealing more than offsets the added purchase costs for a magnetic coupling pump and any out-of-service costs or docking fees have not even been taken into consideration at this point.

A robust and compact design rounds off the pump profile. KRAL is the specialist for maritime applications. KRAL magnetic coupling screw spindle pumps are used on ships as feed and circulation pumps for fuel, lubrication, hydraulic and separator pumps.