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The upper part of the valve stem, within the rocker box, is lubricated by oil. If this oil travels unchecked along the valve stem, engine HC emissions will become excessive. To control this, an elastomeric seal is fitted over the top of the valve guide. These may wear or stiffen with age, so are usually replaced whenever valves are removed for ...
The third cylinder and Gresley gear are visible below the smokebox of this 4-12-2. Gresley conjugated valve gear was used by the American Locomotive Company under license for the 4-12-2 locomotives, the Union Pacific 9000 class, built for the Union Pacific Railroad between 1926 and 1930. These were the largest locomotives to use this valve gear.
These enable a 3-cylinder or 4-cylinder locomotive to be built with only two sets of valve gear. The best known is Gresley conjugated valve gear, used on 3-cylinder locomotives. Walschaerts gear is usually used for the two outside cylinders. Two levers connected to the outside cylinder valve rods drive the valve for the inside cylinder.
Valve seats are often formed by first press-fitting an approximately cylindrical piece of a hardened metal alloy, such as Stellite, into a cast depression in a cylinder head above each eventual valve stem position, [1] and then machining a conical-section surface into the valve seat that will mate with a corresponding conical section of the ...
A crossflow head gives better performance than a Reverse-flow cylinder head (though not as good as a uniflow), but the popular explanation put forward for this — that the gases do not have to change direction and hence are moved into and out of the cylinder more efficiently — is a simplification since there is no continuous flow because of valve opening and closing.
Schematic indicator diagram of pressure in a steam locomotive cylinder. The pressure in the cylinder declines after cutoff as the steam pushes the piston down its bore. Cutoff is one of the four valve events. Early cutoff is used to increase the efficiency of the engine by allowing the steam to expand for the rest of the power stroke, yielding ...
However, these generally have the roller at the point where the cam lobe contacts the rocker, rather than at the point where the rocker contacts the valve stem. Friction may be reduced at the point of contact with the valve stem by a roller tip. A similar arrangement transfers the motion via another roller tip to a second rocker arm.
The poppet valves are controlled by the rotating camshaft at the top. High pressure steam enters, red, and exhausts, yellow. The uniflow type of steam engine uses steam that flows in one direction only in each half of the cylinder. Thermal efficiency is increased by having a temperature gradient along the cylinder. Steam always enters at the ...