Modifications South African Class 5B 4-6-2

1 modifications

1.1 piston valves , smokebox
1.2 trofimoff piston valves
1.3 experimental chimney
1.4 split crossheads
1.5 watson standard boilers

modifications
piston valves , smokebox

in 1930s, a.g. watson, cme of sar @ time, endeavoured improve of older locomotive classes in various ways. class 5b fitted superheating, piston valves , redesigned smokebox arrangement resulted in exhaust has been described positively startling when regulator opened up. @ same time, running boards raised clear of coupled wheels. modification made as-built wheel fairings on running boards unnecessary , resulted in locomotive north american rather british appearance.

trofimoff piston valves

during september 1931, watson fitted engine no. 726 trofimoff type by-pass piston valves experiment. trofimoff valve claimed afford ideal conditions when drifting. on no. 726, experiment less successful and, after having covers blown off couple of times through sudden opening of regulator, trofimoff piston valves removed.

trofimoff valve, closed



trofimoff valve, open

the trofimoff piston valve consisted of 2 fixed discs secured valve spindle, , 2 junk rings, each carrying bull ring , 4 valve rings , both free move longitudinally on spindle. when regulator opened, steam forces loose valve bodies against respective fixed discs , act units, similar ordinary piston valves. when steam shut off, loose valve heads become detached respective discs , remain in idle positions near centre of steam chest, while valve spindle , fixed disks continue reciprocating motion spindle sliding freely through stationary loose valve heads, , steam , exhaust ports in communi­ca­tion. both ends of cylinders in communication, use of ordinary by-bass or snifting valves became unnecessary.

the first such experiment carried out on class 16c no. 851. further similar experiments carried out on class 16b no. 805 in july 1932, class 16da no. 876 in august 1932, class 15ca no. 2852 in march 1933 , on class 15a no. 1961. results of these extended tests did not prove entirely satisfactory , these engines gradually refitted standard piston valves , snifting valves.

experimental chimney

the same locomotive, no. 726, fitted experimental chimney designed watson. similar chimney, shape of earned nickname referred night bucket, tested on class 8d no. 1197. experiment did not result in further production.

split crossheads

in experiment, 1 of class fitted split crossheads. split on vertical centre line , 2 halves bolted on end of piston rod. end of piston rod , nesting inside crosshead halves grooved in arrangement similar nut , bolt, parallel grooves. experiment not success, since rods managed work loose. 1 of front cylinder covers blown off along parts of cylinder , idea abandoned.

watson standard boilers

in 1930s, many serving locomotives reboilered standard boiler type, designed watson part of standardisation policy. such watson standard reboilered locomotives reclassified adding r suffix classification.

only 1 of class 5b locomotives, no. 725, reboilered watson standard no. 1 boiler , reclassified class 5br. while original boiler fitted ramsbottom safety valves, watson standard boiler fitted pop safety valves.

the reboilering required extensive modifications frame under firebox. beatty-designed bridle casting removed , bar frames extended backwards under firebox rear drag box. frame modification turned out weak point in more powerful rebuilt engine, result never again favoured road work , spent of later service life more or less permanently confined culemborg carriage yard.