What are the effects of pressure reversal on magnetic seals?
The standard MAGSEAL designs are limited to maximum pressure reversal of 2 PSID because it is primarily designed to seal pressure in one direction. The MAGSEAL magnet and seal case are a clearance fit into the housing bore and onto the shaft diameter. They are secured to these surfaces by the secondary o-ring seal. When the external pressure is greater than the internal pressure, the magnet and seal case act as a piston and move inboard. The seal faces will then separate when the internal pressure is greater than the external pressure because the resulting force acting on the magnet is greater than the force acting on the seal case. The MAGSEAL design can be configured to operate with pressure reversals up to 30 PSID. This is accomplished by restraining the magnet with a non-magnetic retaining ring in the housing and by using a special seal case design that becomes positively loaded against the seal face when pressure is applied from either direction.
