Abstract: A dry gas seal has a housing with an annularly-shaped channel disposed concentric with the drive shaft, and an inlet to introduce pressurized buffer gas into the housing interior. An annularly-shaped shutdown piston is slidably received in the housing channel for axial shifting, and includes a circumferential seal between its inside and outside surfaces, and an end seal. A biasing member resiliently urges the shutdown piston toward an open position, such that during compressor operation, the forces generated by the biasing member combined with the pressure of the buffer gas acting on the piston's interior face retain the shutdown piston in the open position.

Abstract: A dry gas seal has a housing with an annularly-shaped channel disposed concentric with the drive shaft, and an inlet to introduce pressurized buffer gas into the housing interior. An annularly-shaped shutdown piston is slidably received in the housing channel for axial shifting, and includes a circumferential seal between its inside and outside surfaces, and an end seal. A biasing member resiliently urges the shutdown piston toward an open position, such that during compressor operation, the forces generated by the biasing member combined with the pressure of the buffer gas acting on the piston's interior face retain the shutdown piston in the open position. During compressor shutdown, when the pressure of the buffer gas drops, the pressure of the process gas acting on the piston's exterior face overcomes the combined forces of the biasing member and the buffer gas to shift the shutdown piston to a closed position against an adjacent sealing surface to prevent contaminates from entering the housing interior.