Parker Hannifin high-pressure duplex filters are now specified for the Controllable Pitch Propeller (CPP) systems on four Royal Navy Type 22 Broadsword Class frigates. Late in 1999, the Royal Navy identified a need for improved filtration on the main steering systems of its Batch 3 Type 22 Broadsword Class frigates. The filters fitted when the ships were built were single filters, assembled with check valves and large changeover valves, into a duplex arrangement. This configuration proved to be cumbersome and difficult to use. In addition, support for the products was subsequently withdrawn by the supplier. Discussions with engineers from Parker Filtration and distributor, Rotec Hydraulics, resulted in the Royal Navy commissioning a full minor trial of replacement Parker filter products. This involved the fitting of two Parker Filtration 32PD duplex filters to the CPP systems on HMS Campbeltown. The successful trial improved levels of cleanliness which helps to ensure the long term reliability of the ship. The Parker 32PD high pressure duplex filters operate within the CPP systems at a pressure of 50 bar and flow of 225 litre/min. The fluid is OM33 mineral oil.