Valve Gear Question-Combination Lever

Superheater · **Posted:** Mon Mar 31, 2003 1:02 am

Can anybody explain the purpose of the combination lever on (walshaert or other) valve gear?

I watched the linked animation and it appears to modify the valve events/motion but I can't tell how.

Valve Gear Animation
Superheater@rrmail.com

dave · **Posted:** Mon Mar 31, 2003 7:48 am

It allows for lead to be provided (in both directions) by using the position of the Xhead to alter the position of the valve from that provided by the valve gear.

Dave

Randall Hicks · **Posted:** Mon Mar 31, 2003 11:06 am

> Can anybody explain the purpose of the
> combination lever on (walshaert or other)
> valve gear?

OK, let me try.

The combination lever combines the motion of the valve gear, which is 90 degrees out of phase with the piston, with a small amount of the motion of the crosshead. This biases the actual motion of the valve in favor of forward travel, making the engine more efficient going forward, and presumably less efficient going backwards, but who cares? (Engines weren't designed for the type of service where the train runs out to the end of track in the middle of a cornfield, then backs up to the station again.) I believe that therefore on the cab forwards, which were designed to run in reverse, the combination lever is arranged opposite to the usual fashion. But I could be wrong.

Roger Mitchell · **Posted:** Mon Mar 31, 2003 6:19 pm

The combination lever has no effect on the direction a locomotive will travel or it's performance in either direction. The combination lever is also known as the lead and lap lever and it's job is to provide what is called lead or the opening of the inlet port to the cylinder slightly before top dead center and also compensate for another valve factor called lap which is the distance the valve travels between the opening of either exhaust port.
Roger Mitchell
Master Mechanic
Fort Collins Municipal Railway

http://www.fortnet.org/trolley
n0mcr@netzero.net

RaA · **Posted:** Mon Mar 31, 2003 7:19 pm

It also helps slow down the masses mowing in line with the pistons by letting steam into the cylinder just before the end of the stroke. This is important for the fast runners so their krankpin bearings keep going cold for many kilometers with a minimum of oilconsumption.( using Texaco Meropa 220 for running gear) This presteaminlet is the same in any position of the reverser. With bad walvesetting an locomotive whith a leaky regulator, free brakes and the reverser set at zero may mowe back and forth before it desides to drive in one direction. Demonstrating this for som wannabe firemans is just great fun! I belive they still are setting the Walschaerts gear.
Sorry about the strange spelling - just a norwegian steamlocomotive driver/mechanic.
Ragnar Andenaes