Setting valves

From Frank Williams, Locomotive Valve Setting, 1944:

Valve setting is a term generally applied to the work of making the final accurate adjustments to the valves and the valve gear of a locomotive before it is placed in service. These adjustments are made in order that the positions of the valves shall at all times bear their proper relation to the positions of the pistons. Valve setting follows the erection or hanging of the valve gear by the machinist.

Dead Center

From Frank Williams, Locomotive Valve Setting, 1944:

A locomotive is said to be on a dead center when the center of the main axle, the main crankpin, and the wristpin in the crosshead fall in one straight line. In a locomotive with two cylinders and the cranks set at right angles to each other, there are naturally four positions in which this condition is met. Then the dead centers, taken in order through one complete revolution of the main wheels, are the right front dead center, left front dead-center, right back dead center, and left back dead center.

Valve Formulas

From Larry Koehl, Live Steam Magazine, June 1976

The Throw of Eccentric formula, below, applies only to locomotives using Stephenson valve gear.

Larry suggests adding up to 0.002 inches to the Throw of Eccentric value for each pin in the valve gear (including the eccentric, too) because, even when new, there will be lost motion, possibly enough to eliminate the lead.

Larry also points out the fact that Cut-Off is always 75% when Lap equals Port Width, for all values of Port Width.

External Links

• "Steam Cutoff - Part 1 - Fun with Efficiency", PLS Gazette
• "Steam Cutoff - Part 2 - More Fun With Efficiency", PLS Gazette
• "Finding Locomotive Dead Centers", Jeffrey G. Hook
• "Steam Engine Steam Cutoff Explained"
• Locomotive Valves and Valve Gears, with a Special Treatise on Valve Setting
• Allen Models of Michigan catalog contains a write-up on how to set valves for an Stephenson Valve Gear.
• "The Company Notch", DiscoverLiveSteam.com