The Class 19D was delivered with a Watson Standard no.
1A boiler, fitted with Ross Pop safety valves and set at 200 pounds per square inch (1,379 kilopascals) pressure.
The regulator was of the multiple-valve type, with the valves arranged on the saturated steam side of the superheater header in accordance with SAR practice.
The boiler was one of the range of standard type boilers which were designed by Day's predecessor as CME, A.G. Watson, as part of his standardisation policy.
The locomotive was also equipped with a Watson cab with its distinctive inclined front.

Despite the specifications, the first batch of Class 19D locomotives, built by Krupp and Borsig and delivered in 1937 and 1938, came in two variations.
The Krupp-built locomotives were delivered with domeless boilers, while the Borsig-built locomotives conformed to the specifications with domed boilers.

While the domeless boilers did not conform to the specified Watson Standard no.
1A boiler as far as the dome was concerned, they were accepted nevertheless, probably since all their other dimensions were identical to that of the Watson Standard boiler.
It appears that Krupp had decided on their own accord that a dome was not necessary since there was no regulator in the dome, but merely a standpipe.
Krupp substituted the dome with a manhole cover on which the two Pop safety valves were mounted, while the steam was collected through a battery of collecting pipes, situated high up in the boiler in a similar manner to that which was used in the Class 16E.
All the subsequent Class 19D orders were delivered with domed Watson Standard no.
1A boilers with the usual standpipe steam collector high up in the dome, from where steam was led to the multi-valve regulator in the smokebox.
Technically, whenever the loading gauge permitted the use of domes, their use was preferable to the domeless system which resulted in crowding multiple pipes into the boiler and other complications better left out of boilers.
Operationally, according to drivers, there was no apparent difference in locomotive performance between the two boiler types.

The Watson Standard boilers are interchangeable between locomotives.
In the process of locomotives undergoing major overhauls, these twenty Krupp-built domeless boilers migrated between engines during subsequent years.
As a result, locomotives from the other builders and even some Classes 19A and 19C locomotives eventually ended up with some of these domeless boilers.
The Class 19D was delivered with a Watson Standard no. 1A boiler, fitted with Ross Pop safety valves and set at 200 pounds per square inch (1,379 kilopascals) pressure. The regulator was of the multiple-valve type, with the valves arranged on the saturated steam side of the superheater header in accordance with SAR practice. The boiler was one of the range of standard type boilers which were designed by Day's predecessor as CME, A.G. Watson, as part of his standardisation policy. The locomotive was also equipped with a Watson cab with its distinctive inclined front.
Despite the specifications, the first batch of Class 19D locomotives, built by Krupp and Borsig and delivered in 1937 and 1938, came in two variations. The Krupp-built locomotives were delivered with domeless boilers, while the Borsig-built locomotives conformed to the specifications with domed boilers.
While the domeless boilers did not conform to the specified Watson Standard no. 1A boiler as far as the dome was concerned, they were accepted nevertheless, probably since all their other dimensions were identical to that of the Watson Standard boiler. It appears that Krupp had decided on their own accord that a dome was not necessary since there was no regulator in the dome, but merely a standpipe. Krupp substituted the dome with a manhole cover on which the two Pop safety valves were mounted, while the steam was collected through a battery of collecting pipes, situated high up in the boiler in a similar manner to that which was used in the Class 16E.
All the subsequent Class 19D orders were delivered with domed Watson Standard no. 1A boilers with the usual standpipe steam collector high up in the dome, from where steam was led to the multi-valve regulator in the smokebox. Technically, whenever the loading gauge permitted the use of domes, their use was preferable to the domeless system which resulted in crowding multiple pipes into the boiler and other complications better left out of boilers. Operationally, according to drivers, there was no apparent difference in locomotive performance between the two boiler types.
The Watson Standard boilers are interchangeable between locomotives. In the process of locomotives undergoing major overhauls, these twenty Krupp-built domeless boilers migrated between engines during subsequent years. As a result, locomotives from the other builders and even some Classes 19A and 19C locomotives eventually ended up with some of these domeless boilers.
South African Class 19D 4-8-2