Valves friction

In order to calculate a relief flow area the two-phase mass flow rate per unit area, G, needs to be calculated. Since relief is to be via a safety valve, friction can be neglected and.the equilibrium rate model (ERM) can be used to calculate G (see 9.4.2) . ... 

Comparison of partial stroke curves from past tests can indicate the gradual degradation of valve components. Use of overlay graphics, identification of unhealthy shifts in servodrive, increases in valve friction, and changes in dynamic response provide information leading to a diagnosis of needed maintenance. 

Valve friction coefficient, C/ > (independent of travel for a globe valve) ... 

The method relies on characterizing the pipe and the subsonic valve by frictional losses in velocity heads. The valve frictional loss is given from equations (7.25) and (7.36) as... 

Type of Fitting or Valve Frictional Loss, Number of Velocity Heads, Frictional Loss, Equivalent Length of Straight Pipe in Pipei Diameters, LJD... 

For fittings and valves, frictional losses should be determined using Eq. (2.10-17) and values from Table 2.10-1. 

Valve friction Step response and hysteresis tests... 

Let us note that the fonnation of an apatitic layer in vivo is not desirable for ceramic applications other than for bone substitntes (cardiac valves, friction surfaces of joints). While choosing ceramics for snch apphcations, we have to take care to choose ceramics which do not favor nncleation of these crystals. It has been precisely shown that alpha alnmina is a very bad substrate for the nucleation of calcium phosphates. On the contrary, titaninm nitrides and carbides also proposed as friction strrfaces are qrrite good nncleators [ROY 93] arrd yet these can be questioned with respect to their ttse in friction conples for joirrt repair. 

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