Model Walschaert's Valve Gear

The Walschaerts motion is of the radial type, and it employs link which is trunnioned at its middle point. The link is rocked by means of eccentric rod whose motion is usually driven from a return crank, secured to the main crank pin. The movement of the link is transmitted to the valve stem by a radius rod, whose length is equal to the link radius. This radius rod is pinned to the sliding link block and can be raised or lowered by the reverse lever. When the block is above the link centre, the engine runs in one direction, and when below, the centre, in the opposite direction, the direction of movement being determined by conditions subsequently explained. The return crank on the main pin, known as the eccentric crank, is so set that when the piston is at the extreme end of its stroke, the link stands in the middle position , and it is evident that if the radius rod were attached directly to the valve stem, the valve would also be in its middle position. When, however, the piston is at the end of its stroke, the valve should be displaced from its middle position by an amount equal to the steam lap plus the lead. In the Walschaerts valve gear the valve is given lead by a combining lever which is attached to both the valve stem and the radius rod, and is also connected through a suitable link to the crosshead. This combination lever is so proportioned that if the point of its connection to the radius rod be kept at a stationary fulcrum, and the piston moved, a distance equal to the stroke, the valve will be moved a distance equal to twice the lap plus the lead, therefore, when the piston is at the end if its stroke, the valve is displaced from its middle position, a distance equal to the lap plus the lead, and the correct steam distribution is secured. The Walschaert is a radial valve gear with all motions on the outside of the Loco, this is an advantage in some respects as it can be oiled, examined and repaired more quickly. This gear is often damaged or broken by logs or earth fouling the line.

Category:

Science & Technology

Tags:

• Model
• Walschaert's
• Valve
• Gear

[thebluetrain57]

@robertgift That's right! WTF only 6 secs.?

[robertgift]

Why only 6 seconds?

[mainliner1240]

@Polybun It's very definatly Walschaerts you only need to look at the expansion link

[Polybun]

Looks more like baker gear to me.