This Feldbahn was ordered with a vacuum braking system, including the vacuum limiting valve, as part of the factory build so I expected it to work equally as well as the system that had been installed on the Stafford which I owned previously.  Although the vacuum brakes were being used on the Feldbahn's first run the ejector was somewhat ignored as all the drivers who had a go were preoccupied with trying to maintain enough steam pressure to keep the Feldbahn moving.  No matter what we did, or how much steam blower we used, it was impossible to get the boiler pressure about 85 psi.  Having owned the Stafford for four years and having driven it almost 700 miles the Feldbahn's performance was a real disappointment and so much steam blower was being used to maintain the 85 psi that the consumption of coal and water was almost double that of the Stafford.  The second run started out in the same fashion until I tried running without the vacuum brake system operating.  Instantly the Feldbahn came alive and the boiler pressure easily stabilised at almost 120 psi, in fact once on the move no steam blower was required and the firebox door had to be kept slightly open to stop the safety valve constantly blowing off.  After trying it for themselves several different drivers all came to the same conclusion as I had; the vacuum braking system was pressurising the smokebox and preventing the boiler from steaming properly.  I already knew that the ejector exhausted its steam directly through a gland in the side of the smokebox which was identical to the system that had worked so well on the Stafford, so why was this engine performing so differently ?  Obviously I was going to have to experiment to overcome the problem.

The first experiment was to direct the ejector exhaust up the funnel.  In this photo you can see where the ejector exhaust entered the smokebox via the dirty gland nut at the top left corner of the photo.  As supplied there was nothing attached to this gland so the exhaust steam just rushed into the smokebox (which was exactly the same as it had been on the Stafford).  I tried running the Feldbahn with the ejector exhaust steam fed through the new pipe shown in the photo, but not surprisingly it operated exactly the same as the steam blower did and the fire was now uncontrollable.   After a couple of laps of the Pinewood track with the safety valve blowing constantly despite the steam blower being turned off this experiment was deemed a failure.

The next experiment was to simply dump the ejector exhaust steam directly into the open air, so for this the pipe shown on the left was used to take the exhaust underneath the footplate.  The black painted bar at the bottom of the photo held the pipe firmly in place as it was retained by one of the existing cab side bolts.  This configuration made a significant improvement as the Feldbahn now steamed happily, and when compared to operating without the vacuum braking system in use only a small amount of additional steam blower was required to maintain the boiler pressure at 120 psi when running with the vacuum brakes operating.  The possible downside to this configuration was that a constant plume of steam was being noisly discharged from under the footplate as shown in the photo. The experiments had already shown that to maintain a vacuum of 15 in Hg the ejector required quite a lot of steam with the standard control valve having to be opened about 1/8 to 1/4 of a turn.  In contrast the ejector fitted to the Stafford had required much less steam, and because the steam valve had to be opened so little (it was almost impossible to adjust it for the minimum amount of steam required) I had actually fitted a fine control needle valve to the Stafford.  So far as I could tell the ejector fitted to the Feldbahn was using far more steam than that supplied with the Stafford, and presumably that was why it pressurised the smokebox and so severely limited the ability of the boiler to raise steam. This was as far as my experiments progressed in 2014.  I knew what was wrong with the vacuum braking system supplied by Station Road Steam but despite talking with them neither of us knew why it was so different to that which had operated faultlessly on the Stafford.

For the 2015 running season something had to be done.  So far as I could tell the problem was being caused by the ejector apparently requiring far more steam to operate than the ejector fitted to the Stafford had required.  PNP Railways manufacture an ejector which they claim has "a low steam consumption" and can operate at boiler pressures up to 120 psi so I decided to purchase one and see how that worked.  The photo on the left shows the Feldbahn vacuum brake ejector system as supplied by Station Road Steam.  The ejector (ringed in blue) is designed to work in the vertical plane so all the pipes connecting to it run either straight up or down.  The problem with the PNP ejector was that it required the vacuum pipe section (containing the non return valve) to be vertical but the other connections are then in the horizontal plane.  You can see this in the photo on the right where the ejector is again ringed in blue. The installation of this ejector required a lot of new pipes to be made, and as it was supposed to use less steam I decided to fit a small steam valve to give finer control of the steam supply to the ejector in the same way as I had on the Stafford.  Thankfully the steam manifold already had a spare port in it's end above the firebox door so the needle valve was fitted there and plumbed into the ejector steam pipe using a "T" piece connector. On test this PNP ejector was found to use less steam than the original Station Road Steam item, which wasn't surprising as inspection had shown that the hole in its steam cone was just under half the diameter of the original one.  Currently the large (original) steam valve is only used to create the initial vacuum in the train pipe and coaching stock.  Once the required 15 in Hg is achieved the large steam valve is completely closed and the needle valve is opened about 3/16 to 1/2 a turn depending on how much the coaching stocks vacuum system leaks.  This still gives quite a cloud of steam under the footplate but at least the sound of escaping steam is much less than it had been.  The obvious question is, could the ejector exhaust now be put back into the smokebox ?  Sadly at the moment I can't be bothered to find out as I'm busy with other projects but if I do ever get around to further experiments then this page will relate what happens.