What is California Cut-Off ?
Steam engines admit steam only during a portion of the stroke. As the steam expands, it converts the heat of the steam into work.
While starting the boat from rest, steam is admitted for 60 or 70 percent of the stroke. However when cruising, steam is admitted for as little as 15 or 20 percent of the stroke. This uses only a small amount of steam, and consequently provides great fuel economy.
Various valve gears were used on the Mississippi riverboats, these included the Sweeney, Rees, Stephenson and Walschaert. The most sophisticated was the California cut-off.
Most engines were fitted with pressure balanced poppet valves operated by four lifting beams. One intake and one exhaust valve at each end of the cylinder. As the beams were lifted by the gear, the valves were opened to admit steam or allow the steam to exhaust.
The California variable cut-off has a wedge fitted to the top of the intake beams. The position of the wedge controls the amount of steam admitted to the cylinder. The cut-off is infinitely adjustable and can be changed rapidly for different conditions.