by Bradypus Nick

Al long title for a simple little device.

In my page on 'Bodging a body for Lawley' I mentioned that I had added a draincock simluator and promised to add a few details when I fitted one to Wrekin, so here they are, only 11 months later!

The main objective was to avoid the shower of oily water which splattered everywhere when the loco starts from cold, so the exhaust from the cylinders is closed off completely and sent downwards to two pipes posing as draincocks.

Think of the Thames Barrier...

The heart of the device is a rotary gate valve. Like the Thames Flood Barrier, it has a rotating segment which is used to block the  path to different ports. In our case, the exhaust and a pair of drain pipes. Diagrammatically, it looks like this:


The shaded segment is part of a rotating bar through the centre of the valve, actuated by a servo.

In the flesh it looks like:


The body is 1/2in brass hexagon soldered to a 1/8in thick base which is a close fit over the Accuscraft exhaust stub and steam inlet stub. The latter keeps it located squarely. One vertical hole through carries the exhaust, while two closely spaced holes in the front flat lead to the drain.

A hole is drilled lengthwise through the body to take the rotary part which is 1/4in brass bar. the bar is relieved in the middle to make the segment shown in the diagram and squared off at one end to take the actuating lever.

Similar metals working together is not usually recommended but there is plenty of wet steam around and there isn't much movement. Anyway, brass is easier to file to shape than anything harder.

The Accuraft exhaust pipe is truncated and screwed into the top while two 3/32 dia. copper drain pipes soldered to the body point downwards and forwards either side of the reverse valve. As the valve lives in the bottom of the smokebox, all the joints are silver soldered.

The whole thing is placed over the Accucraft reverse valve block and gooed in place with a dab of silicone sealer.

In position it looks like:

Yes it is at a slight angle- the base moved while I was soldering it!

Although it blocks part of the burner exhaust slot in the base of the smokebox it doesn't seem to have any effect on the performance of the burner.

Having diverted the water downwards and sideways, it only remains to provide the draincock effect. Underneath we have some more copper pipes, soft soldered to some simple brass brackets and coupled to the valve by some rather violent coloured, but fortunately hidden, silicone tube:


The plate under the reverse valve is a mk.1 clamp for the divert valve, since deleted. (And, by the way- the brass lump behind the bufferbeam is only the whistle.)

Outside, the effect is completed:


The upper pipe projecting from under the cylinder is the 3/32in. dia drainpipe which, hopefully, looks as though it comes from the front draincock while the lower pipe is a dummy 1/16in. dia pipe simulating the rear draincock.  A smear of black paint rubbed on and polished off helps to disguise the fact that they are different diameters. In use, it is dificult to tell which pipe the steam comes out of!

Finally, the lever on the valve is linked to a cheap micro servo in the tank. There is very little pressure on the valve so any small servo will do.  I have linked mine to channel 5 on a Planet 2.4GHz set, so the valve is either "on" or "off" (fully open or fully closed). This means that there is no exhaust when the 'draincocks' are open but does keep all the oily water off the paintwork so the main objective is achieved! Moving to a channel with proportional control or providing a bleed passage in the valve would allow some 'chuff' while draining the bulk of the water away.