The UK's ‘Queen Elizabeth’ class aircraft carriers are the second-largest class of warships in the world. Fresh drinking water can be required for up to 2300 personnel.
The UK's ‘Queen Elizabeth’ class aircraft carriers are the second-largest class of warships in the world. Fresh drinking water can be required for up to 2300 personnel.

Aircraft carriers are hugely impressive in size and bring their own challenges. One being to keep their crew supplied with fresh water. This meant having an RO plant requiring minimal maintenance. Two Danfoss APP 8.2 pumps running in parallel, provided the solution with competitive capital costs, low operating costs and reliability.

Two new UK aircraft carriers, HMS Queen Elizabeth and HMS Prince of Wales, each rely on three seawater RO desalination plants for fresh water production. With a displacement of 65,000 tons and length of 280 meters, the Queen Elizabeth class aircraft carriers are the largest warships ever constructed for the UK’s Royal Navy, and the second-largest class of warships in the world. Fresh drinking water is a critical resource for the ship’s company of about 700, and for up to 1600 embarked personnel. It is also indispensable for showers, cooking, dishwashers and general ship husbandry. 

The new aircraft carrier class was designed from the bottom up for efficiency. In order to reduce running costs, the Aircraft Carrier Alliance and the Royal Navy placed great emphasis on maximizing crew productivity. The number of persons required to run each ship, 700, is exactly the same as their predecessor’s, the Invincible class, which measures just one third in size. Operating a ship three times larger with the same size crew required stringent attention to a vast spectrum of details, and resulted in an unprecedented use of automation and other technological innovations.

Minimal maintenance
For fresh water production, this meant the ship’s RO plant had to be designed for minimal maintenance. Like everything else on a ship, footprint and weight were also important criteria. Finally, total costs of ownership were highly scrutinized. Salt Separation Services, who provided the plant, turned to Danfoss APP technology for reliable low-maintenance performance and a minimal footprint

Salt Separation Services was an early adaptor of Danfoss APP technology, and knows the advantages of axial piston pump technology better than most. “As a company with deep roots in the marine and offshore segments, we took an early interest in the APP’s very compact footprint. We trialed some of the very first APP pumps as far back as 2002,” explains director Daniel Shackleton, “and we currently have APP pumps running in over one hundred RO plants for the Royal Navy alone. Their long service intervals, dependable reliability and overall cost competitiveness made them a natural for this new application. At the time of bidding, the APP 8.2 had the largest capacity in the Danfoss portfolio, so we designed each plant around two APP 8.2 pumps running in parallel.”

Operating costs
The competitive capital costs met the demands for low operating costs and reliability to win bid Salt Separation Services won the project, and Shackleton is convinced that the APPs played a key role in evaluations. “There’s no getting around the fact that fewer moving parts equates to less maintenance, reduced manpower hours and fewer worries,” he says.

 “The APP pumps require no belts, discharge pulsation dampeners or in-line suction dampeners and, importantly, there is no lubrication to schedule or contaminate. There’s just less upkeep involved.” With 8000-hour service intervals for the high-pressure pumps, automatic RO membrane flushing and advanced remote monitoring, and just one marine engineer takes care of the water plant for up to 1600 shipmates.” 

“The flexibility APPs provide for marine applications is another advantage,” adds Shackleton. “They’re compact and can be installed either vertically or horizontally and each pump weighs just half of a reciprocating pump of similar capacity, so they’re far easier to work with and ship.” •