This leakage is arrested by O-Ring or gasket.Īlthough the main closing force on primary seal faces is normally provided by the pressure in the stuffing box, some force is required to keep them closed during startup and shutdown and to take care of the shaft movement. If shaft sleeve is used, one more static leakage path will be there between shaft and shaft sleeve. These leakage paths are sealed by elastomers, PTFE, gasket, etc. The last two are jointly referred to as the “Tertiary Seal”, and both are fairly simple seals as there is no relative motion between the two parts involved. Metallic bellows are used for high temperature application. Leakage at secondary seal is arrested by a dynamic O-Ring, sliding wedge or a bellow (elastomeric, PTFE or metallic). There is always invisible leakage in vapour form between the faces.īetween the Rotating Face and the Shaft (Secondary Seal),īetween the Stationary Face and the Gland, and Thus mechanical seal is not a zero leakage seal. These vapours keep on escaping to the atmosphere. Since both the surfaces are continuously moving with respect to each other, there is heat generation which keeps on evaporating the liquid film and new liquid film is formed. This leakage path is sealed by providing absolutely flat mating surfaces perpendicular to rotating shaft centre line where they come in contact and maintaining healthy lubrication film between the two mating faces. This is the first and most important of the four possible leak paths (Primary Seal). The rotating face is secured to the pump shaft while the stationary face is held in the gland. It has two flat faces running against each other. In this blog, information is given on working of a mechanical seal, types of mechanical seals, methods of environment control, equipment parameters, installation instructions, start-up procedure and check list for identifying causes of seal leakage.Ī basic mechanical seal is a simple device. Because of the absence of visible leakage, environment is clean and hazard free when mechanical seals are used. However the power consumed, maintenance and downtime spent in renewing or tightening the compression packing overweigh the initial cost of a mechanical seal, which works unattended for a long time. The initial cost of a mechanical seal is high as compared to compression packing. Compression packing works on the principle of controlled leakage whereas mechanical seal tend to seal with no visible leakage. Modern process equipment with rotating shafts (such as pumps and compressors) are equipped with compression packing or mechanical seal to minimize emission of the process fluid into the atmosphere.

Mechanical stuffing boxes