<P> Saturated steam is advantageous in heat transfer due to the high latent heat of vaporization . It is a very efficient mode of heat transfer . In layman's terms, saturated steam is at it's dew point at the corresponding T and P . The typical latent heat of vaporization (or condensation) is 970 Btu / lb for saturated steam at atmospheric pressure . </P> <P> Superheated steam was widely used in main line steam locomotives . Saturated steam has three main disadvantages in a steam engine: it contains small droplets of water which have to be periodically drained from the cylinders; being precisely at the boiling point of water for the boiler pressure in use, it inevitably condenses to some extent in the steam pipes and cylinders outside the boiler, causing a disproportionate loss of steam volume as it does so; and it places a heavy demand on the boiler because a large amount of water has to be evaporated per unit volume of steam . </P> <P> Superheating the steam dries it effectively, raises its temperature to a point where condensation is much less likely and increases its volume significantly . Added together, these factors increase the power and economy of the locomotive . The main disadvantages are the added complexity and cost of the superheater tubing and the adverse effect that the "dry" steam has on lubrication of moving components such as the steam valves . Shunting locomotives did not generally use superheating . </P> <P> The normal arrangement involved taking steam after the regulator valve and passing it through long superheater tubes inside specially large firetubes of the boiler . The superheater tubes had a reverse ("torpedo") bend at the firebox end so that the steam had to pass the length of the boiler at least twice, picking up heat as it did so . </P>

The saturation temperature of steam with increase in pressure increases