TourTourBearing performance of a mechanical seal with tapered film
 
 Diameter 2R0   10-3 m
 Diameter 2R1   10-3 m
 Film thickness h0   10-6 m
 Film thickness h1   10-6 m
 Supply pressure pS   106 Pa
 Ambient pressure pA   106 Pa
 Viscosity η   Pas
 
ISO 724 Load capacity F'=F/(A(pS-pA))  
 Flow rate Q'  
 Stiffness S'  
 Load capacity F   N
 Flow rate Q   10-6 l/min
 Inherent stiffness S=-dF/dh   106 N/m
 
In mechanical seal technology the dimensionless load F' is called the pressure gradient factor k1. With parallel film k1=0.5 and S=0. A tapered film shows axial bearing stiffness and can be considered as a hydrostatic collar bearing.

Face seal patterns for liquid and gas seals are applied to obtain full film lubrication even with parallel film. Spiral grooved seals are applicable only for one direction of rotation. A variety of alternative patterns are suitable for two directions of rotation (Figure 10.8). Gas seals require relative high surface speeds or large seal areas to separate the seal faces because of the low viscosity of gases. It is why in some gas handling machines a more compact liquid seal with lubricant system is constructed.

 
Pressure distribution in a "U-groove" gas seal (left) and in a "U-groove" liquid seal (right). Full film lubrication is obtained by the compressibility of the gas and by cavitation in the liquid respectively.

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