Mechanical seal provides a sealing between a rotatable shaft and a housing. The seal has a stationary part for connection to the housing and a rotary part for rotation with the shaft. Mating sealing faces are carried by the stationary and rotary parts and the rotary parts are mounted on the drive shaft for rotation therewith. Each sealing face is held relatively stationary to their respective stationary or rotary part by means of at least one link member extending therebetween. The link member is arranged for at least limited longitudinal rotation.
A mechanical seal comprises a "floating" component which is mounted axially movably around the rotary shaft of, for example a pump and a "static" component which is axially fixed, typically being secured to a housing. The floating component has a flat annular end face, i.e. its seal face, directed towards a complementary seal face of the static component. The floating component is urged towards the static component to close the seal faces together to form a sliding face seal, usually by means of one or more springs. In use, one of the floating and static components rotates; this component is therefore referred to as the rotary component. The other of the floating and static components does not rotate and is referred to as the stationary component.
Those seals whose floating component is rotary are described as rotary seals. If the floating component is stationary, the seal is referred to as a stationary seal.
If the sliding seal between the rotary and stationary components are assembled and pre-set prior to despatch from the mechanical seal manufacturing premises, the industry terminology for this is "cartridge seal". If however the rotary and stationary components are despatched individually (unassembled) from the mechanical seal manufacturing premises, the industry terminology for this is "component seal".
Seal faces are generally held to their relevant stationary or rotary components by a mechanism that is called drive ring. One of the common mechanisms is the use of slots on the back of seal face and lugs on the drive ring or vice versa. FIG. 1 shows four slots on the seal face and four lugs on the drive ring. FIG. 2 shows two lugs on the seal face and two lugs on the drive ring. Rotation will be transferred from the seal faces to the drive ring at rotary faces or vice versa at the stationary faces.
Seal faces are mainly supplied from various grades of silicon carbide, tungsten carbide, ceramics and carbon. Carbon is categorised as a soft face.
The contact between the slots and lugs is mainly point contact. Under point contact, soft or brittle seal faces are more prone to failure than hard faces, especially in high pressure and large seal size applications. The failure may start by notch propagation around the contact point which gradually grows until it destroys the seal face.
Instead of having lugs on the drive ring, some designs employ drive pins that are pressed firmly into holes in the drive ring. These pins cannot move or rotate from their location. FIG. 3-2 illustrates the use of two pins to drive a lug on the seal face when the seal rotates either in clockwise or counter-clockwise direction. If the mechanical seal is designed to only rotate in one direction, one pin can be used for each lug. Alternatively, the pin may be square, cylindrical or any other shape
The pin's head may have different shapes which are related to the contact area at the slot. FIG. 6 illustrates a different shape for the head of the floating pin illustrates a different contact area between the floating pin and its relevant slot.
The type of drive can be switched for rotary and stationary faces according to application. Similarly, some pieces of equipment such as shaft and pin in FIG. 8 may be stationary and the other pin may be rotary. It should be understood that the invention may be used with metallic components as well as nonmetallic components.
Depending upon the application of the seal, a floating pin of the present invention may be located at any position or angle relative to the seal faces.It should be understood that the invention may be employed for either rotary or stationary seals and single or double mechanical seal, whether designed in a cartridge or component seal format.