[5] Szlumper had a dual career as a railway engineer, laying out some of key lines linking the major routes to the wider countryside of Wales and the West.

When he took the job of Surveyor to the county of Cardiganshire, he also held the role of deputy engineer of the Manchester and Milford Railway, which never reached either of the locations in its title, being restricted to a line between Strata Florida and Pencader, Carmarthenshire.

[6] However, he became good friends with the line's manager James Cholmeley Russell, and resultantly later became civil engineer to the North Wales Narrow Gauge Railways and in 1906 became a director.

On 31 December 1868, Szlumper was appointed Chief Engineer of the Whitland & Taf Vale Railway (W&TVR), having been recommended by business partner and Member of Parliament David Davies.

The W&TVR was closely aligned to the Pembroke and Tenby Railway (P&TR), having a virtually common set of investors and board of directors.

The board felt Szlumper had not fulfilled his duties properly, particularly after incorrectly engineering the M&MR junction at Pencader which was investigated by the Railway Inspectorate.

1072,[11] his long-term friends included Mary of Teck, the Queen Consort of George V.[12] Szlumper died on 27 October 1926 and is buried in Richmond Cemetery (Section O, grave number 2414).