The pressure double end mechanical seal (i. e. Face-to-Face double end face mechanical seal) has two pairs of friction pairs, complex structure, need external sealing fluid system, the sealing cavity into the isolation fluid (0.5-1.5) x105Pa higher than the medium pressure, plugging, lubrication and other functions. The isolation fluid lubricates the inside seal.

　　No pressure double end mechanical sealing (Face-to-back series mechanical seal) has two friction, complex structure, need external sealing liquid system, sealing buffer in the cavity is not pressurized, the process medium lubrication inside sealing, no pressure double end mechanical sealing, use rise year after year, this seal can be widely used for vinyl chloride, carbon monoxide, light hydrocarbon and other drugs volatile and dangerous medium.

　　No pressure double end sealing mechanical sealing inside sealing "the first seal" is the main seal, equivalent to a single end surface packing seal, the lubrication fluid is borne by the sealed medium, the sealing cavity is filled with liquid from the sealing tank, not pressurized, inside sealing seal failure lead to the pressure of the sealing chamber increase, can by the pressure gauge, record or the alarm, while the external seal can seal and hold the leaking liquid before repair.