Moel Tryfan and her sister engine Snowdon Ranger were 0-6-4 side tank locomotives constructed by the Vulcan Foundry Ltd in 1875 (builder's numbers 738 and 739 respectively).
They were built for the North Wales Narrow Gauge Railways, and were of the Single Fairlie type, nominally designed by C.E. Spooner.
In 1917, Snowdon Ranger's frames were placed under Moel Tryfan to provide one good locomotive from the two. However, the North Wales Narrow Gauge Railways closed later that year.
When the Welsh Highland Railway opened in 1923, Moel Tryfan was cut down to enable it to work over the Ffestiniog Railway (the Ffestiniog Railway's loading gauge is much more restrictive than the Welsh Highland's).
In 1937, Moel Tryfan was at Boston Lodge for boiler and firebox repairs and remained there until 1954. Having survived until the dawning of the era of preservation, Moel Tryfan (almost certainly the only remaining Single Fairlie left in this country) was borken up for scrap by the Ffestiniog Railway, who at the time were desperately short of funds.
The bogie frame, one side tank sheet, the pony truck wheels, and the air receiver are all that remains of Moel Tryfan. Although Russell had worked on the N.W.N.G.R., it was in fact owned by the Portmadoc, Beddgelert and South Snowdon Railway Co. Therefore these few remaining items are all that is left of the once-proud N.W.N.G.R. locomotive stud. The pony truck wheels are under Linda and Blanche, on the Ffestiniog Railway.