During the nineteen-thirties the larger turbines from 35,000 to 60,000 kW at 1500 r.p.m. continued to be made, and also a growing number of self-contained units' both condensing and Pass-out types, for outputs from 250 to 6000 kW. A three-cylinder 105,000-kW 1500-r.p.m. turbine installed in the Battersea power station in 1935 is still famous as the largest single-axis unit ever built in Europe. This machine has a low pressure cylinder of the double flow type with a multiexhaust in each flow and is equipped with central-flow twin condensers and fivestage feed heating incorporating a single-effect evaporator.

The Battersea set represented, perhaps, the final development of the straightforward 1500-r.p.m. machine, and thereafter much work was devoted to increasing the output obtainable at 3000 r.p.m.

A range of modern sm^G cy{mdeT 3000-r.p.m. turbines was developed from two machines, a 6500-kW condensing unit and a 7500-kW pass-out unit, built in 1933. These turbines were subsequently made in outputs up to 24,000 kW for large industrial plants and for the smaller power stations at home and abroad.

For general power station practice a two-cylinder 3000-r.p.m. turbine with a double-flow low pressure cylinder was designed, and in 1934 four 33,000-kW units of this type were put in hand, three for the Klip power station in the Transvaal and one for Belfast. Since then more than forty turbines of the same type have been ordered. At Klip twelve similar sets were installed altogether, giving (with four 7000-kW house sets) an aggregate capacity of 424,000 kW; in 1940 no less than 2566 million units were sent out, considerably more than from any British station.

The use of double flow construction depends, however, on the conditions at the exhaust. For moderate vacuum and steam quantity it is possible to use a single-flow low pressure cylinder with a multi-exhaust, and after experience had been gained in rebuilding the two-cylinder sets at North Tees for 50-c/s operation three 30,750-kW 3000-r.p.m. turbines of this type were designed and installed at Manchester, and another at Croydon.

Steam conditions were to be notably changed as a result of pioneer work by Baumann, Guy, and their assistants on the economic benefits obtainable from higher steam pressures. Inlet steam conditions of 600 p.s.i.g. and 800-850°F had been the accepted practice, and the limiting factor was the maximum temperature that could be employed with the materials available; to advance pressures without a corresponding increase in temperature would have resulted in excessive condensation