Rasmus Folsø
Senior Vice President - New Green Solutions
New DesFuel – Deepwell (RSL) Pump: the features to handle any alternative fuel
September 2025
What makes the DesFuel – Deepwell Pump ideally suited for any alternative fuel in shipping – now and in future? Read this article to discover the key technical features of our new deepwell fuel pump range, plus the benefits they give you. The new DesFuel – Deepwell (RSL) range of fuel pumps from DESMI helps you reduce emissions from ships by facilitating the use of alternative fuels including LNG, NH3, LPG/LEG, and MeOH. The pumps give you the flexibility to switch to different fuels in future.
Despite the extreme characteristics of these fuels, the technical features of the pumps ensure safe and economical handling whilst also making service and maintenance very easy for crews and service technicians. This article introduces you to these features and the benefits they provide.
High-performance pump from experienced manufacturer
The DesFuel – Deepwell pumps (RSL) are specially designed for alternative fuels on a wide range of ships. The pumps are designed according to the IGF and IGC code, complying with major marine class society rules and regulations. The design fulfils all requirements for installation in EX zones 0 (inside the tank) and 1 (outside the tank).
The pumps are manufactured from AISI304/304L stainless steel and offer a wide flow range, allowing operation at low flow rates. This helps reduce the need for fuel recirculation or throttling, ensuring efficient performance.
The DesFuel – Deepwell (RSL) pump is designed for 3,500 RPM but can handle pump speeds in excess of 4,000 RPM. Depending on the pump, it can reach heads above 450 mlc (metres of liquid column; 1476 feet of liquid column) with a true NPSHr value even below 0.5 mlc (1.64 feet of liquid column) depending on the point on the pump curve, which means it will start and run at low tank levels. The pump will work with tank pressures up to 20+ bar (290+ PSI).
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Tested with liquid nitrogen at -196°C (-320°F), the DesFuel – Deepwell Pump (RSL) is well suited for handling LNG at -165°C (-265°F) and other types of liquefied gas fuels. This makes the pump suitable for any alternative fuel. You can control pump speed using a VFD to adapt pump speed quickly and continuously to engine load changes. |
With more than 250,000 pumps in service around the globe, DESMI is a trusted and experienced manufacturer. The DesFuel – Deepwell (RSL) range is inspired by our DesCargo – Deepwell pumps that have proven their capability and reliability in the global marine industry since 1996. We manufacture the DesFuel pumps at our high-quality facilities in China, close to many of the world’s leading shipyards, reducing shipping cost, time, and risk and also lowers carbon emissions.
Service-friendly outside-the-tank solution
On a DesFuel - Deepwell (RSL) pump, the drive unit (2), coupling (3), and bearing housing (4) are located outside the tank, making service and maintenance significantly easier and more cost-effective. In addition, service intervals are long (25,000h MTBR), and no service work is foreseen between dockings. Technicians can easily carry out visual and auditive inspections and feel how the pump is running by detecting vibrations.
The multi-stage pump cylinder (6) and inducer (7) are located at the bottom of the fuel tank. The patented foot valve (8) at the bottom of the caisson pipe is designed in such a way that impurities in the fuel have no effect on the closing mechanism. The valve can therefore be sealed shut very effectively, allowing the pump to be retracted for inspection and repairs without gas freeing the tank; a process that would otherwise be very costly and time-consuming.
The easy access to the DesFuel pump contrasts with cryogenic submerged pump designs where the motor, coupling, and bearing are located at the bottom of the fuel tank.
The outside-the-tank design of a DesFuel - Deepwell (RSL) pump has been optimised for safe and efficient fuel handling. The top flange with balancing valves (5) ensures the pressure and liquid level of the caisson pipe is equal to that of the tank. And because the motor (1) is located outside the fuel tank, it transmits negligible energy to the fuel, thereby reducing boil-off gas.
Completely sealed with magnetic coupling
The DesFuel – Deepwell Pump (RSL) features a completely leakage-free design that ensures safe and efficient handling of challenging or hazardous alternative fuels. Instead of a traditional pump coupling and shaft seal, DesFuel pumps have a magnetic coupling that ensures a completely sealed fuel system. It segregates the tank gas phase from the surrounding environment whilst ensuring efficient transfer of power from the drive unit to the pump stages.
The magnetic couplings are DESMI’s own mag-drive design that offers a wide torque range: Standard pumps provide up to 430 Nm at 40°C and 25 bar of pressure (317 ft-lbs at 104°F and 363 PSI), and customised solutions provide even more torque. This gives the pump sufficient power for handling heavy liquids or providing high flow rates and pump heads.
Long-life oil-lubricated bearings
DesFuel – Deepwell (RSL) pumps have a thrust bearing arrangement with double preloaded bearings that handle axial load in both directions: accommodating both the downward weight of the pump and the upward lifting force generated from below during operation.
The bearings are lubricated using oil, not the pumped fuel. This means you get consistent lubrication performance no matter which fuel is used, and it means the bearings are not exposed to excessive wear due to fuel impurities. Both of these benefits contribute to long service lifetime for the bearings and the pump. In addition, oil change intervals are long (5 years or 25,000 hours), and it is easy to fill lubrication oil.
The lubrication system in the DesFuel pump bearing housing has an industry-standard oil filter that can quickly and easily be replaced at sea, as can the lubrication oil itself. The bearing arrangement can easily be replaced if necessary, and the built-in impeller in the housing ensures uninterrupted oil circulation. You can monitor the state of the bearing using the PT100 temperature sensor and optional vibration sensor.
The DesFuel pump bearing housing can be fitted with an optional heater (EX design) which ensures that high-pressure fuels like LPG and NH3 do not condensate in the bearing area when temperatures run low. This also contributes to longer bearing life and improved pump performance.
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Easy and efficient sealing of components outside the tank
The entire pump base of a DesFuel - Deepwell (RSL) pump can be disassembled for repairs or replacement without gas freeing the tank first: The pump features a pneumatic static seal mounted below the bearing housing. The seal efficiently seals off the components above from the gas in the tank, allowing you to work on the drive unit, magnetic coupling, and bearing housing.
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Wide selection of discharge flanges
The DesFuel - Deepwell (RSL) pump is available with discharge flanges that comply with a wide selection of flange standards and are machined to different type standards.
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Revolutionary intermediate pipe design
The intermediate pipe of a DesFuel – Deepwell (RSL) pump includes a revolutionary design feature that takes deepwell fuel pumps to the next level: Our patented guide bearing supports pipe sections with a length up to 3,000 mm each as the bearings are not connected to the pipe flanges. This makes installation and service of the DesFuel pump significantly easier because fewer sections are needed to achieve the desired pipe length, and bearings can still be installed close to each other as per API 610 requirements.
Pipe sections are available in sizes down to 500 mm, making it easier to select section lengths that perfectly match your vessel: If the pump base is located in a tank connection space with limited height, shorter sections facilitate disassembly. By contrast, longer sections reduce pipe weight and the number of flanges in open-deck installations with no pipe length limitations.
New cylinder design with efficient inlet seal
At the bottom of the fuel tank, the pump cylinder of a DesFuel – Deepwell (RSL) pump features a new CFD-aided design, the inducer, and one to nine pump stages, depending on your performance requirements.
The patented foot valve at the bottom of the caisson pipe features a perforated plate that acts as a strainer, preventing larger items from reaching the pump. Smaller fuel impurities can be filtered out using a filter located outside the tank. The inlet can be closed easily, securely, and efficiently, enabling you to retrieve the pump cylinder from the tank for inspection and service without gas freeing the tank first.
Learn more about the future of alternative fuels
The technical features of the DesFuel – Deepwell (RSL) pump combine to maximise reliability and safety, even in challenging operating conditions, no matter which alternative fuel you are using – and no matter which alternative fuel you may decide to use in future. The pump offers long service intervals, with no planned service between dockings – a definite advantage for ships on long international voyages – and the whole pump can be serviced without gas freeing the tank.
Not only does the pump provide optimal fuel flexibility; it also supports easy installation and disassembly – and Nordan Marine, a DESMI company, is ready to support you globally with all necessary documentation, warranties, after-sales packages, and service agreements.
The DesFuel – Deepwell (RSL) Pump quite simply is the future of alternative fuel supply systems in shipping. Contact us to learn more!