the 34 fluid trapping region 48 34 the opposed field configuration also minimizes magnetic fields outside the device 10 and provides maximum resistance to weakening of the sealing gap fields by externally imposed magnetic fields a larger number of ring magnets can be used but two is a sufficient number if the energy in each is high enough when the device is assembled and end cap 34 is joined to housing 12 by an epoxy or other adhesive applied at interface 19 a measured amount of fluid not shown sufficient to fill a limited number of sealing gaps 50 is placed on the shaft in the 34 secondary sealing region 34 46 and the shaft is inserted into the pole piece when the fluid wetted section enters the pole piece the fluid spreads evenly around the shaft 16 filling the gaps and forming isolated pockets of trapped air in the sealing gaps or grooves 50 of the shaft a pressure differential is applied across the assembly vacuum pumping on the flanged end and some fluid is drawn further into the 34 primary sealing region 34 28 it has been determined that only a few e g four stages are required to support the full pressure differential 1 atmosphere provided the magnetic field strength is high enough in the 34 primary sealing region 34 the sealing gaps 44 in the 34 secondary sealing region 34 also provide some degree of sealing although these stages will be weaker than in the 34 primary sealing region 34 because the field strength in these gaps is less some gaps at the left side of the 34 primary sealing region 34 may never be filled with fluid in normal operation at the.