The steam turbine driven propellant pump is the heart of the Walter 109 series motor. Powered by the oxidisation of one of the on-board propellants, the pump delivers the large masses of liquid which the rocket motor requires for operation.

The small size of the motor, and the large mass flow of propellant required an efficient yet compact unit, and the twin centrifugal pumps delivered the required performance. The centrifugal pumps were designed by Jaeger of Leipzig and the steam turbine which drives the unit by Brückner Kanis of Dresden, who were responsible for the production, assembly and testing of pumps. More correctly, the unit should be referred to as the "WK9 Pump" unit.

Pictured here is the Walter Fuel Pump on display in the Deutsches Museum in Munich. The WK9 bi-fuel pump consists of a single, continuous drive shaft carrying a central single-stage steam turbine, on each side of which is a centrifugal pump, each primed by a screw-type booster stage. The illustration shows the pump from the T-Stoff side, with the spline for the accessory gearbox drive nearest the left, and the steam turbine housing in the centre.

Both pumps are mounted in a series of aluminium castings which form the pump casing, sealed with a complex arrangement of seals to prevent the leakage of C-Stoff, T-Stoff and steam.

The illustration shown here is taken from a wartime report on the Walter motor - although the annotations have been enlarged to make them clearer. For a more detailed view, use the illustration below to see a higher resolution picture.

The turbine disc and shaft are formed from a single forging of high tensile steel. The overall diameter of the shaft is 8.8in and its maximum operating speed is 16,000 rpm.

There are 76 impulse blades and these have a dowel shaped root which is held in a groove in the turbine disc circumference. A cut away allows blades to be fitted by inserting them at this point and then sliding them around the groove. A master blade is last to be fitted into the insertion point, and is held in place by a pin. The turbine blade tips are held by a shroud ring.

During operation, steam from the steam generator is directed onto the turbine blades through a small nozzle. After passing through the blades, the steam is then turned back on itself by a series of six guide vanes and is directed back through the turbine blades at a later point around the circumference. By passing the steam back through the turbine in this way, some increase in efficiency is obtained by velocity compounding, and there is an additional benefit in that this will also tend towards balancing out the end loads on the turbine.

A higher efficiency for the steam turbine would have been obtained by adding a whole second stage turbine, but the steam consumption represents such a small portion of the total T-Stoff consumption of the motor that the additional complication of a two stage turbine was not considered justified.

Exhaust steam exiting the turbine chamber is passed overboard through a short pipe, which emerges on the underside of the Komet rear fuselage.

Both propellant pumps are centrifugal type impellers, fluids being drawn in at the face and driven outwards at pressure to the circumference. The pumps themselves are aluminium, double shrouded impellers, keyed onto the turbine shaft.

There are dimensional differences between the impellors of each pump, specifically in the diameter and outlet area. This is because the T-Stoff volume flow required is about twice that of C-Stoff although the delivery pressures are roughly the same, whilst the specific gravity of each propellant is different.

Shown here is the C-Stoff pump.

Keyed onto the turbine shaft immediately before each impellor is a helical booster stage which is designed to keep the propellant pumps primed with propellant. Centrifugal pumps have a poor suction characteristic and the helical booster induces a flow towards the pump. As each booster is at an opposing side of the turbine, the end thrust effect of one balances out that of the other so the effort required from the turbine thrust bearing is minimised.

In this picture of a preserved WK9, the C-Stoff pump is shown (see the impeller above), and the helical booster pump is clearly visible just at the C-Stoff inlet, as a double thread screw. This photograph is available as a higher resolution picture by clicking on it.

The WK9 is a compact, power efficient unit, as the single drive shaft simultaneously runs both propellant pumps. However, as both propellants are drawn into a common unit, the sealing arrangements for C-Stoff and T-Stoff pumps had to be very elaborate. Inadvertant mixing of the propellants at this point would be catastrophic. Not only that, the T-Stoff had to be kept from leaking towards the oil lubricants in the turbine shaft bearings, and the oil prevented from migrating towards the T-Stoff pump.

The high speeds and very low weight demanded of the engineering meant that the C-Stoff pump was not leak-proof, and indeed, leakage past the rubbing surfaces of the pump amounted to about 8% of the C-Stoff throughput. Leaked propellant was collected in a chamber in the casing and piped back to the fuel tanks. Although a complex system of cylinder jackets, ring seals and synthetic rubber diaphragms was used to prevent C-Stoff escaping, a residual leak was still present. This was drained to atmosphere and was acceptable at a level of below 0.045 pints per minute.

The T-Stoff pump is sealed in a similar fashion, with a similar 0.045 pints per minute residual leakage being channelled into the exhaust steam outlet.

Both oil from the bearings and residual steam from the turbine are sealed against leakage by various means. The leaking steam is collected in a chamber in the turbine housing, and channelled away to exhaust with the leaking T-Stoff (there is no problem about mixing steam with T-Stoff as the former is derived from the latter). Much greater care is taken not to allow steam to reach the nearby turbine shaft roller bearing, as there may be some residual T-Stoff in the steam, and upon contact with the oil in the bearing, the result would be an instantaneous explosive decomposition of the T-Stoff.

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