The diagram above shows the standard section of a rubber diaphragm seal. The shaft seal is provided by the rubber diaphragm which is squeezed onto the shaft by the drive ring. Once fitted, the rubber diaphragm will grip the shaft giving a strong static seal and very positive drive, via the drive ring, to the seal face.

As there is no relative movement between the shaft and the rubber diaphragm, shaft fretting, wear and hang-up hysteresis are eliminated and the seal can immediately accommodate some shaft run-out and misalignment.

Shaft axial movement and the movement required during the working life of the seal is handled by the elastomer rubber flexing at its junction point (Red Area on diagram). The seal head automatically adjusts to compensate for any face misalignment, usually caused by shaft end float / pump body misalignment.

The closing spring force and the seal pumping pressure force maintain the faces in full contact, whilst the rubber diaphragm acts as an elastomeric bellows providing sustained flexibility. The positive drive of the seal face is transmitted via the drive ring and retaining housing, and not via the spring, which merely provides some closing force to the mechanical seal faces. These seals can therefore be used to seal shafts rotating in either direction and in vacuum applications.