Mechanical Seals 机械式密封教程.pptVIP

DUAL SEALS Since the outside or secondary seal runs in a non-pressurized clean lubricating liquid, it will generally last for an extended period of time. When the inside or primary seal fails, the leakage through the faces will be contained by the secondary seal until the pump can be shut down for seal replacement. Failure indication and shutdown devices can be attached to the buffer supply so that the pump operators know when the primary seal has failed. DUAL SEALS When pumping volatile liquids, hazardous, corrosive, abrasive, etc. it is sometimes necessary to insure that the process liquid does not enter the atmosphere or the artificial environment created for the seal or even the seal faces. Pressurizing the artificial environment, 20 to 30 psi. above the pump stuffing box pressure will prevent process liquid from crossing the primary seal faces. Instead, boundary layer film liquid is supplied to the primary seal by the artificial environment or “Barrier”. The arrangement of seals can be the same as a non-pressurized in most cases. The difference is in how the seals perform. In a pressurized dual seal, the outboard or secondary has the tougher job of the two. It operates sealing high barrier pressure while the inboard or primary seal has clean lubricating liquid applied at differential pressure of only 20 to 30 psi. Now let’s look at the environmental controls for operating dual seals. Pressurized Dual Seal Artificial Environment “Barrier” System Non-Pressurized Dual Seal Artificial Environment “Buffer” System TO FLARE / RECOVERY SYSTEM DISCHARGE SUCTION NON-PRESSURIZEDBUFFER FLUIDPLAN 52 / 7352 PRESSURIZED BARRIER FLUIDPLAN 53 / 7353 PRESSURIZED GAS IN DISCHARGE SUCTION DUAL SEALS There are many more types of environmental control arrangements that are discussed in other programs. This presentation simply covers the basics. For more detailed information on this topic, contact your supervisor or a Sealing Technologies Representative. SPLIT SEALS Some types