A motor comprising a frame for supporting a rotor assembly and a stator assembly, the frame comprising an inner wall and an outer wall and a plurality of diffuser vanes extending between the inner wall and outer wall; a rotor assembly comprising a shaft, a magnet, a bearing assembly and an impeller; and a stator assembly comprising a bobbin, a stator core and a winding wound round the bobbin; the impeller comprising a metal hub and an outer portion, the outer portion comprising a plurality of blades and being formed of plastic or carbon fibre composite.

A method for pressure and temperature control of fluid in a series of cryogenic compressors. An actual speed for each compressor and an actual inlet pressure and actual inlet temperature at entry are determined. The maximum speed for each compressor and a desired inlet pressure for the first compressor is provided. A speed index for each compressor is determined from the maximum speed and actual speed of each compressor. A proportional value is determined from the deviation of the actual and desired inlet pressure. A priority value is determined from the smaller of the proportional value and the smallest speed index. A desired inlet temperature for the first compressor and a desired speed for each compressor are determined from the priority value. The actual inlet temperature is adjusted to the determined desired inlet temperature and the actual speed for each compressor is adjusted to the determined desired speed.

A method for controlling speeds of compressors arranged in series for compressing a fluid. The desired inlet pressure is predefined and the actual inlet pressure is detected. The actual discharge pressure of the fluid is recorded and the actual total pressure ratio is recorded. A proportional integral value is determined from the deviation of the actual inlet pressure from the desired inlet pressure and a capacity factor is determined from the proportional integral value and the actual total pressure ratio. A model total pressure ratio is determined from the actual total pressure ratio and the capacity factor. A reduced desired speed for each compressor is determined as a function value of the control function associated with the respective compressor. The control function assigns a reduced desired speed to each value pair of capacity factor and model total pressure ratio and is used to adjust the speed of each compressor.

A flow control device for constraining fluid flow between axial flow turbomachines in series has a flow constrainer which constrains the fluid flow downstream of the first turbomachine in the series to the blades region of the second turbomachine, preventing fluid flow from impacting the hub or nosecone of the second turbomachine and providing more uniform fluid flow to the second turbomachine. The flow control device includes connective elements for positioning between the downstream region of the first turbomachine and the upstream region of the second turbomachine. The device may be equipped with stator vanes having a variety of optional configurations to further improve the uniformity of the fluid flow load on the second turbomachine.