Thermal Cycling In Mechanical Seals — Causes, Prediction, Prevention

Abstract

Thermal cycling in mechanical seals is the periodic variation of face temperature during operation. Periods have been observed from one to several seconds. Thermal cycling can cause increased leakage and accelerated wear.

Seal designers primary goal is for stable operation. However, at present, there is no useful theory, which allows designers to anticipate and design around thermal cycling. A recent attempt to model such a thermal instability in hydrostatic seals (Ref 5), predicted an extremely short oscillation period (a few milliseconds), which is considerably at odds with observations.

Tne present paper considers a more comprehensive seal interface model to solve the complete two dimensional transient heat transfer, resulting thermal distortions, and interface fluid and contact load supports in an interactive manner.

Given certain ranges of operating conditions and design parameters the model demonstrates a seal’s susceptibility to thermal cycling. The predicted frequency of cycling, and details of the response agree very closely with measurements of a seal operating in mineral oil.

The method presented here allows seal designers to design around thermal cycling and its damaging effects, to give the most consistent seal behaviour and hence improved reliability.