Designed by LBSC, and described in his book "Shop Shed and Road", I've made two Everlasting blowdown valves for blowing down the boiler.
A normal needle valve could be sufficient, but because I have to mount them on the back of the boiler, it would be difficult to operate the valve. This design of an 'Everlasting' blow down valve overcomes this problem; it is operated by a lever. Everlasting does not say anything about the valve's lifespan (although it should be trouble-free for a long time according to LBSC); it is the name of an American company who makes (and still do) these valves, and on which LBSC's design was based.
I've made a slightly scaled up design, suitable for the 7¼" gauge loco. The actual valve opening is 4 mm in diameter. The main halves of the valve body are turned from bronze rod.
On the in-let part a M10 x 1 mm thread was cut out of center, with the aid of the 4 jaw chuck.
On the out-let part all the holes were bored and a thread was cut (M7 x 1) for the connection the blow down pipe. By doing this in one set-up, all the positions and orientations are according the drawing. I wonder how LBSC made this, without all the dimensions on his drawing and without the comfort of a digital read out on his milling machine.
On the CNC milling machine the outside contour was cut to size.
The difference between the cut and un-cut parts. That is the nice thing is about CNC milling that you can just watch how the part is made.
The milling program first cuts the contour in a spiral movement and finishes it, with a light cut of 0.5 mm down to the final dimension. This gives a smooth surface.
The parts were screwed on a temporary fixture with some M3 bolts
The in- and out-let halves of the valve body completed.
The valve arm, cut from solid brass and later parted off from this block with a saw cutting blade in the milling machine.
With a home made punch, the square hole was opened up. A small spindle will operate this valve arm.
The valve arm in position in the out-let halve of the valve body. Only a turn of about 30 degrees will quickly fully open the valve. Judging by what I've read in locomotive operating manuals, this valve enables the fireman to briefly blow down the loco boiler during the run or while waiting on a siding. This way the boiler could be cleared of scale and sediment which settles on the foundation ring, without having to blow down entirely.
The square ends milled on the spindle with a small dividing head.
The spindle, just before parting off from the stainless steel rod.
The spindle, valve arm and a Teflon valve seat. In the original description by LBSC, he used bronze or stainless steel for the valve seat. But in those days Teflon was not available.
A quick set-up for CNC milling the operating lever.
The two completed valves, the left one in opened position and the right one closed.
The final assembly with a small packing ring on the spindle and the remaining screws has to be still taken care off.
Completed with a small handle.
The position of the valves, just beneath the footplate.
