Baker valve gear
Encyclopedia
Baker valve gear was the main competitor to Walschaerts valve gear for steam locomotive
s in the United States. Strictly speaking it was not a valve gear
but a variable expansion mechanism adapted to the Walschaerts layout replacing the expansion link and sliding die block. The Baker arrangement used more pivot bearings or pin joints, but avoided the die slip inherent to the expansion link, with the aim of lessening wear and the need for service; it could also facilitate longer valve travel.
and Franklin patterns were used on a few classes, but only the Baker pattern won more than limited acceptance.
The design originated in the A.D. Baker Company, of Swanton, Ohio
; a builder of steam traction engines. The idea came from an employee called Gifford but was developed by the Baker company with the first patents being issued in 1903.
The Baker Locomotive Valve Gear was produced by the Pilliod Co. of Swanton, Ohio. Subsequent versions were produced up to the end of steam service. It was particularly popular on the Norfolk and Western Railway
, and almost all later N&W engines used it (notably NW 611
). Other extensive users included the Chesapeake and Ohio Railroad and the Nickel Plate Road
. The New York Central Railroad
and the Baltimore and Ohio Railroad
also had large classes which used Baker gear. There was always heated debate about the claimed advantages of Baker gear, the main criticism being the number of pin joints and possible lost motion. Western United States and British railroads tended to prefer to continue with the Walschaerts pattern, as did the Pennsylvania Railroad
. In Britain Baker gear was popular amongst model engineers but in full-size practice the length of the yoke and the width of the assembly may have been difficult to accommodate within the restricted loading gauge.
The Baker mechanism consisted of the following parts:
The parts were arranged so that when the yoke was centered, the connection of the main link to the bellcrank was in a line with the two pivots on the yoke. At this point, the back and forth motion of the lower end of the main link left the top relatively motionless as main link swung back and forth on the swing links.
In forward motion, the yoke was pushed forward, so that its upper pivot was in front of the bell crank-main link connection. Moving the eccentric arm back and forth lowered and raised the top of the main link. This motion was translated by the bellcrank into back and forth motion of the radius rod. The angle of the yoke controlled the relative motion, and therefore the cutoff; tilting the yoke backwards reversed the motion of the radius rod.
Steam locomotive
A steam locomotive is a railway locomotive that produces its power through a steam engine. These locomotives are fueled by burning some combustible material, usually coal, wood or oil, to produce steam in a boiler, which drives the steam engine...
s in the United States. Strictly speaking it was not a valve gear
Valve gear
The valve gear of a steam engine is the mechanism that operates the inlet and exhaust valves to admit steam into the cylinder and allow exhaust steam to escape, respectively, at the correct points in the cycle...
but a variable expansion mechanism adapted to the Walschaerts layout replacing the expansion link and sliding die block. The Baker arrangement used more pivot bearings or pin joints, but avoided the die slip inherent to the expansion link, with the aim of lessening wear and the need for service; it could also facilitate longer valve travel.
History
In the very early 1900s there were many efforts to create a new valve gear to replace the by-then-standard Walschaerts valve gear. In the United States the Young, Southern, CaprottiCaprotti valve gear
The Caprotti valve gear is a type of steam engine valve gear invented in the early 1920's by Italian architect and engineer Arturo Caprotti. It uses camshafts and poppet valves rather than the piston valves used in other valve gear...
and Franklin patterns were used on a few classes, but only the Baker pattern won more than limited acceptance.
The design originated in the A.D. Baker Company, of Swanton, Ohio
Swanton, Ohio
Swanton is a village in Fulton and Lucas counties in the U.S. state of Ohio. The population was 3,690 at the 2010 census.-History:A.D. Baker, a steam engine inventor, ran a machine shop in Swanton from 1901 to 1953.-Geography:...
; a builder of steam traction engines. The idea came from an employee called Gifford but was developed by the Baker company with the first patents being issued in 1903.
The Baker Locomotive Valve Gear was produced by the Pilliod Co. of Swanton, Ohio. Subsequent versions were produced up to the end of steam service. It was particularly popular on the Norfolk and Western Railway
Norfolk and Western Railway
The Norfolk and Western Railway , a US class I railroad, was formed by more than 200 railroad mergers between 1838 and 1982. It had headquarters in Roanoke, Virginia for most of its 150 year existence....
, and almost all later N&W engines used it (notably NW 611
Norfolk and Western 611
Norfolk and Western Railway's J class steam locomotives were a class of 4-8-4 locomotives built by the Norfolk and Western Railway's East End Shops in Roanoke, Virginia, between 1941 and 1950 Norfolk and Western Railway. The first batch, numbered 600 to 604, were built in 1941–42 and were delivered...
). Other extensive users included the Chesapeake and Ohio Railroad and the Nickel Plate Road
New York, Chicago and St. Louis Railroad
The New York, Chicago and St. Louis Railroad , abbreviated NYC&St.L, was a railroad that operated in the mid-central United States. Commonly referred to as the Nickel Plate Road, the railroad served a large area, including trackage in the states of New York, Pennsylvania, Ohio, Indiana, and Illinois...
. The New York Central Railroad
New York Central Railroad
The New York Central Railroad , known simply as the New York Central in its publicity, was a railroad operating in the Northeastern United States...
and the Baltimore and Ohio Railroad
Baltimore and Ohio Railroad
The Baltimore and Ohio Railroad was one of the oldest railroads in the United States and the first common carrier railroad. It came into being mostly because the city of Baltimore wanted to compete with the newly constructed Erie Canal and another canal being proposed by Pennsylvania, which...
also had large classes which used Baker gear. There was always heated debate about the claimed advantages of Baker gear, the main criticism being the number of pin joints and possible lost motion. Western United States and British railroads tended to prefer to continue with the Walschaerts pattern, as did the Pennsylvania Railroad
Pennsylvania Railroad
The Pennsylvania Railroad was an American Class I railroad, founded in 1846. Commonly referred to as the "Pennsy", the PRR was headquartered in Philadelphia, Pennsylvania....
. In Britain Baker gear was popular amongst model engineers but in full-size practice the length of the yoke and the width of the assembly may have been difficult to accommodate within the restricted loading gauge.
Operation
The Baker valve gear replaces the expansion link of the Walschaerts gear with an assembly of levers and links which produces the same effect of allowing continuous variation valve travel. The remainder of the gear is the same, so that the return crank and combination lever take the same form, although the proportions are usually modified. The Pilliod Co. sold the gear as a single assembly which was mounted on the frame in the location ordinarily occupied by the Walschaerts expansion link.The Baker mechanism consisted of the following parts:
- A frame which replaced the mounting for the expansion link. It came in two basic forms, depending upon whether it was attached to the locomotive frame at both ends or only at the front. In either case it had two pivots: one forward and at the top of the frame, and one below and to the rear.
- A U-shaped reversing yoke which tilted back and forth to control reversing and cutoff. The ends of the yoke's arms pivoted on the rear frame mount, and there was also another pivot mounted near the base of the arm. The yoke was connected at the top to the reach rod leading to the reverser.
- A pair of swing links which hung from the upper pivot on the yoke.
- A main link which pivoted in the middle from the lower end of the swing links and whose lower end was connected to the eccentric rod (which in turn connects to the return crank on the driver, as in the Walschaert gear). This link had a characteristic "J"-shape.
- A bellcrank whose center pivot was the upper, forward mount on the frame, and whose ends were attached to the top of the main link and the radius rod (the connection to the combination arm and thence to the valve).
The parts were arranged so that when the yoke was centered, the connection of the main link to the bellcrank was in a line with the two pivots on the yoke. At this point, the back and forth motion of the lower end of the main link left the top relatively motionless as main link swung back and forth on the swing links.
In forward motion, the yoke was pushed forward, so that its upper pivot was in front of the bell crank-main link connection. Moving the eccentric arm back and forth lowered and raised the top of the main link. This motion was translated by the bellcrank into back and forth motion of the radius rod. The angle of the yoke controlled the relative motion, and therefore the cutoff; tilting the yoke backwards reversed the motion of the radius rod.
External links
- Spare parts brochure from the Pilliod Co. showing the gear mounted on a locomotive and the various models available