H17 Left: H17-206 was built in 1925 by Henschel, on the Schmidt high pressure system. 4-6-0 Boiler Pressure: 1000 psi (60 kp/cm2) Coal-fired. Compound. HP cyl diam 290 mm LP cyl diam 500 mm The H17-206 was not repeated.

H17 Left: Side elevation of the H17 The long HP steam drum is above the firebox.

H02	H stands for Hochdruck- German for high pressure.

After the failure of the H17, you might be surprised that another German high-pressure loco was attempted. There was a good reason. Conventional locos were at the limit of the power that could be generated within the German loading gauge; wheels and boilers had reached maximum possible size.

Above: the high-pressure locomotive H02-1001, built in 1929. Note the small diameter of the outside cylinders. The chimney is set well back from the front of the boiler; smoke can be seen emerging in line with the front driving wheel.

The designers of this beauty meant business; steam was delivered at no less than 1750 lb/sqin (105 kp/cm) to the two very small outside cylinders of 220mm diameter, compounded with a single 600mm LP inside cylinder. Wheel arrangement was 4-6-2.
It was delivered in 1930 by Schwarzkopff, built to the design of Dr L Löffler. Schwarzkopff were brave enough to guarantee in the purchase contract a coal saving of 42% over a standard 01 design; in fact DRG never bought the loco.

Above: The steam circuit of H02. The firebox tubes carried steam only.

A Injector	K pump lockoff valve	S rotary pump	1 Air preheater
B,C setback valves (?)	L throttle valve	T heat exchanger	2 hot air duct
D HP regulator	M LP regulator	U oil separator	3 LP feed heater
E changeover valve	N HP cylinders	V condensate reservoir	4 feed pump
F security valve	O LP cylinder	W steam generator
G lockoff valve (?)	P LP superheater	X steam introduction
H overflow valve	Q HP superheater	Y saturated steam withdrawal
I blowoff valve	R HP feedheater	Z external steam inlet

The plumbing of H02 was complex, and one begins to get some idea of why maintenance costs were high. Briefly, this is how it worked...
The Schmidt system avoided scaling in the HP boiler by transferring the firebox heat through a distilled-water ultra-HP circuit. The Schwarzkopff-Löffler instead used steam alone to transfer the heat; steam cannot of course deposit scale.
Saturated steam from steam generator W was pumped through the HP superheater tubes Q which lined the firebox. There it was superheated to about 900 degF and the pressure raised to 1700 psi. Only a quarter of this was fed to the HP cylinders; the rest was returned to the steam generator to evaporate more water and continue the cycle.
The HP cylinder exhaust passed through the oil separator U, the LP feed heater 3, and then the tubes of the LP boiler T; this latter is roughly equivalent to the LP boiler in the Schmidt system, but is not heated by combustion gases. Steam was raised at here 225 psi, fed to the LP superheater, and then fed via the LP regulator M to the LP cylinder. The LP exhaust feeds the blastpipe in the smokebox.
The HP exhaust condensed in the LP boiler heating tubes was pumped back to the steam generator W.

This is all very ingenious, but contains a hidden snag... it is impossible to raise steam in this loco unless you already have steam available from somewhere else. Since the firebox tubes are cooled by steam and not water, the minimum pressure in the steam generator before the fire could be lit was 70 psi. Steam could be introduced from another locomotive by via the external steam inlet Z.

Another point is that you are absolutely dependant on the steam pump to keep going. This is probably why two were fitted, but it doesn't seem to have helped reliability much.

Above: H02-1001 on a turntable.

As with other high-pressure experiments, after extensive trials it was found that the increase in efficiency was small compared with the greatly increased costs. H02-1001 was also hopelessly unreliable. No more were built.

H02 Left: Another view of H02, without its tender. The headlight also seems to be missing.