The quantity of T-Stoff which is delivered to the steam generator for decomposition to drive the turbine of the propellant pump, is determined by the steam control valve, a unit which is fitted in the by-pass line between the main T-Stoff delivery pipe and the steam generator.

The steam control unit is easy to spot. It is positioned in Walter "A-1" and "A-2" series motors on the inside port face of the thrust plate. It is a rectangular, natural metal object, topped with two cylinders. The pilot's throttle is connected via a mechanical rod and linkage to a lever joined to the main control cylinder in the steam control valve. The unit has pipe inlets for T-Stoff and C-Stoff at pump pressure.

Most observed units have an external pointer moving against a graduated scale, inscribed in the body of the casting, or on an external plate. Although the exact purpose of this is as yet unknown, it is probably a means of monitoring adjustments or of calibration.

The steam control valve itself is an aluminium casting, the interior of which is anodised and coated with wax. This wax lining is to prevent any catalytic effect on the T-Stoff by impurities in the casting, and to prevent corrosion.

Along the bottom of the unit is a cylinder lined with a hardened steel sleeve, cut with slots. Within this is a hardened steel barrel, capable of rotating through 100^o, and connected to the pilot's throttle.

Two series of slots are milled into the barrel, corresponding to slots cut in to the fixed sleeve.

T-Stoff at pump pressure enters the cavity of the barrel and depending on the angle of rotation, exits through either the idling slots furthest from the inlet, or the main delivery slots.

Idling.

Above the idling slots, at ninety degrees to the main control barrel, is a cylinder. This cylinder also has a hardened steel liner, shrunk and pressed in, with holes in the circumference which lead into a common channel in the main body of the casting.

A hollow piston is free to move in this cylinder. It also has holes drilled in its circumference which correspond with the holes in the liner, allowing fluid to pass through from the centre of the piston, out to the common channel.

There is a lip at the top of the piston, which acts as a stop, such that when the piston is at its lowest position the holes are aligned opposite each other, fully open. The piston is loaded in the downward position by a spring, adjustable for tension with a nut.

As the liquid passes to the steam generator, the turbine accelerates and pressure of T-Stoff in the steam control valve increases. The piston, driven by the increasing propellant pressure, rises in the barrel cutting down the port area. The piston stop is adjusted so that with the rotating barrel opened 20^o the piston travel is limited to give a propellant pump delivery pressure of 25 atmospheres.

Main delivery.

The liquid which passes through the main slots of the rotating barrel enters the main body of the casting, into the common channel. However, it can only exit the steam control valve by passing through another cylinder, set parallel to the idling cylinder.

This cylinder also has a liner and moveable piston. The exit port for the T-Stoff is aligned with the common channel, and the piston in this cylinder is narrowed at the waist, leaving a gap for the free flow of liquid to the T-Stoff delivery line.

The piston is spring-loaded at the top, and on the bottom face has a small diameter cup. This covers a hole bored in the bottom of the cylinder which is connected to T-Stoff at pressure. If the pressure of T-Stoff increases, the piston will be raised off its seat. At this point, the surface area upon which the T-Stoff acts will be increased, and the upward force on the piston will rise very suddenly - this will snap the piston rapidly upwards, raising the waisted section beyond the common channel, quickly shutting off the propellant flow.

The piston is held held onto its seating by means of a spring and a mechanical stop. At the other end of the stop is a synthetic rubber diaphragm fitted into a dome section on the top of the valve body.

C-Stoff at pump pressure is fed to the chamber at the top of the diaphragm, with a similar pipe acting as drain, leading back to pump inlet line. This means that the piston is fed at its lower end with T-Stoff at pressure, and on the top face by a function of the C-Stoff pressure.

Now it can be seen that if T-Stoff flow fails, the steam generator will be starved of propellant and the system will halt. If there is a failure in C-Stoff flow, pressure on the top of the main delivery steam control valve piston will be lowered. This piston will then lift under T-Stoff pressure and snap closed, shutting off the main T-Stoff flow and preventing any overspeeding of the turbine.

Shown here on the left, is the Steam Control Valve from the 109-509.A-2 at the Museum of Flight, East Fortune in Scotland.

The springs which operate the pistons in the control valve act through push rods working in synthetic rubber seals. This is a precaution against T-Stoff leaking past the adjusting screw of the idling valve to atmosphere; or in the case of the quick acting valve, of coming into contact with the C-Stoff side. Any leakage past the valves is channelled through the casting body into a propellant drain which leads to the turbine exhaust pipe.

In the T-Stoff delivery outlet line of the steam control unit, is a non-return valve. This is required during starting, when propellant pressure has not had time to build up in the line. If there was no valve, steam pressure in the steam generator would pass back along the T-Stoff line.

In the body of the non-return valve is a throttling orifice. This is set to control the flow of fluid, and thus the maximum speed of the turbine pumps. This fixes the upper limit of the thrust of which the motor is capable.

The maximum flow could be set by adjusting the size of the slots in the rotating barrel, but the orifice has proved to be a much more convenient and satisfactory method.

Two views of the Steam Control Valve on the Washington Walter show the control rod and linkage. It also shows the T-Stoff output line curving up from the inboard side of the valve over and into the top of the Steam Generator.

These two views of the same Steam Control Valve (on the Shuttleworth Walter) also show the control rod and linkage. In close-up is the plate, marked in levels;
0, 1, 5, 10, 15, 18, 21.

As a contrast, this is the Steam Control Valve on the Walter 109-509.C motor currently on display in the RAF Museum, Cosford. It shows that there are obviously two sections served by control rods: an upper and a lower section.

The method of operation is discussed in the section on the USAF HWK 109-509.B-1.

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