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### Poppet Seal Gasket O-ring Operating Life and Reliability Equations and Calculator

Poppet Seal Gasket Oring Operating Life and Reliability Equations and Calculator

The primary failure mode of a seal is leakage, and the following equation is a approach developed for evaluating a poppet valve design.

Poppet valve seal reliability equation:

Where:

λSE = Failure rate of seal, failures/million cycles
λSP,B = Base failure rate of seal, failures/million cycles
K1 = Constant = 3.27 x 10-4
P1 = System pressure, lb/in2
P2 = Standard atmospheric pressure or downstream pressure, lb/in2
Qf = Allowable leakage rate under conditions of usage, in3/min
?a = Absolute fluid viscosity, lb-min/in2
ri = Inside radius of circular interface, in
ro= Outside radius of circular interface, in
H = Conductance parameter (Meyer hardness M; contact pressure C; surface finish ƒ), in

The conductance parameter is a combination of Meyer hardness, contact pressure and surface finish per the following equation:

Where:

M = Meyer hardness (or Young's modulus) for rubber and resilient materials, lbs/in2
C = Contact stress, lbs/in2
ƒ = Surface finish, in

In the case of an O-ring seal, the failure rate will increase as a function of time because of gradual hardening of the rubber material. A typical failure rate curve for an O-ring is shown below:

References:

Handbook of Reliability Prediction Procedures for Machine Equipment

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