10 THE CALL BOARD NEWSLETTER OF THE MOHAWK & HUDSON CHAPTER, N.R.H.S.

The Walschaerts Valve GearBy Don Barbeau

In the early 1970's, the Mohawk & HudsonChapter sponsored outings on theCooperstown and Charlotte Valley Railroad.The featured attraction was CACV 0-6-0 No.2 (Aleo 1942), and because of the causalenvironment at Cooperstown, we were ableto observe her close up as she assembledher train. We saw the little engine proceedtoward us and stop. We then heard a whir-ring sound (the power reverse) and saw avalve gear component (one on each side)lift radially. Once the throttle valve wasagain opened, the little 0-6-0 backed awayfrom us, all because one valve gear compo-nent was realigned.

The particular valve gear on CACV No.2 is known as Walschaerts Valve Gear. Ourdiagram shows the gear in forward position,Typical of most later design steam locomo-tives, the valve gear is set "directly", whichmeans that, in forward, the radius rod andthe eccentric rod travel in the same direc-

tion. This is accomplished by utilizing thebottom half of the link for forward motion(the link being center pivoted).

Please note the components as shown inthe diagram. There is an eccentric crank setfast to the crank pin of the main drivingwheel. As the driving wheel rotates, the ec-centric rotation of the crank imparts travelto the link via the eccentric rod. The linkrocks back and forth once with each driv-ing wheel rortation. The action of the linkimparts travel via the radius rod to the steamdistribution valve in the steam chest.

Let us presume that the little 0-6-0, aftermoving forward, stopped with her near sidecylinder in mid-stroke, with the crank pinat its lowest position. The first cut-away dia-gram (above) shows the position of the pis-ton in the cylinder and the position of thespool valve in the chest. Note that while thepiston is in the center, the spool valve istoward the front of the steam chest. This is

due to the angle of the link. If steam is ad-mitted into the steam chest from the throttle(not shown), it will flow through the frontpassage into the cylinder, where it will actupon the front face of the piston. This willpush the piston toward the rear of the cylin-der and rotate the driving wheels so as tocause the locomotive to move forward.

Now let us presume that, instead of for-ward position, the radius rod was raised (bythe lifting lever) to the top of the link, whileall other components remained in the sameposition, as in the second cut-away. Nowthe angle of the link causes the spool valveto be at the rear of the steam chest. If steamis admitted, it will be channeled by the spoolvalve through the rear passage into the cyl-inder, where it will act against the rear faceof the piston and propel the engine back-wards.

If the crank pin were at its top position,with the radius rod in the down (forward)

In a previous time, CACV No.2 was Virginia Blue Ridge Railway No.8. Here she is at Piney River (Va.) in March 1960.But is she going backward or forward? Read our valve gear article and you'll know immediately. (Photo by DonBarbeau)

NEWSLETTER OF THE MOHAWK & HUDSON CHAPTER, N.R.H.S. THE CALL BOARD 11

- Wo./.scho.er+s Vo./ve Gear D;~ram -

L;t+;~ LeverLink

&<:drll.,.ic

S+eo.tn Che.s+1/1111 Ro.dius RocJ

C1l,'rld erCornbino.l,·o,., J.eve,.-

position, as in the third cut-away, the angleof the link would be reversed and the spoolvalve would be at the rear of the steam chest.The piston would then be pushed forward,driving the locomotive forward also, as itshould.

The other function of thecontrol the speed of the locomtrolling the four cylinder "evradius rod is raised part way("hooked up"), the amourr 0

raidus rod and spool valve is ret::ncee..directly affects (1) the amount ofseeara th,,-

is admitted to the cylinder; (_)which the steam flow is cut off: ellh"~nf1~at which the expanded steam is Irl!~~ asexhaust; and (4) the amount 0

steam that is retained in the cylinder for com-pression in order to cushion the piston as itnears the end of its stroke. (The more the

. gear is hooked up, the faster the locomotivecan run.)

Thus far we have neglected the functionof the combination lever. This device, some-times known as the "lap and lead" lever, isactivated by the crosshead through the unionlink. The combination lever imparts addi-ional travel to the spool valve, but unlike

zravel imparted by the link, this lever'se.; constant It is primarily responsible

for supplying the necessary valve "lead" thatthe steam to the cylinder an instant

ore the piston completes its previouse" This supplies an additional "kick" at

the outset of the return stroke.Since the right side driving wheels are a

quarter turn ahead of the left side wheels(relative to crank pin position), the valvegear on each side functions independently.Yet the lifting levers are fastened to a com-mon shaft to ensure identical settings on bothsides so as to avoid unequal power thrusts.

Regarding CACV No.2, whose valvegear we used for our explanation, she is onstatic display in Cooperstown at the railroadstation. If you're ever in that area, stop byand take a look at her and her valve gear.

P.S. Check the photo again. The radiusrod is up. The little locomotive was backingover the crossing.