External balanced mechanical seal

The invention discloses an externally-mounted balanced mechanical seal which comprises a sealing assembly, the sealing assembly is arranged around a rotating shaft, the rotating shaft is fixedly sleeved with a shaft sleeve, an annular cavity is formed between the sealing assembly and the shaft sleeve and is of a necking-down type structure, and the outer end of the annular cavity is communicated with a pump head cavity. The outer end face of the sealing assembly and the shaft sleeve form an annular cavity, and a liquid filling cavity is formed between the inner end face of the sealing assembly and the shell. Due to the formation of the annular cavity, the impact force of a medium in the pump head on the sealing assembly is reduced, sealing failure is avoided, the flowing buffering area of the medium in the cavity of the pump head is increased, and the high pressure resistance of the pump is improved; even if the medium in the pump head cavity permeates into the pump body through the sealing mechanism, the med