In 1876, the two pits were merged under the combined Bwlfa and Merthyr Dare Coal Company. After a series of accidents criticised by the
HM Inspectorate of Mines, seeking new investment the company reformed as the Bwllfa and Merthyr Dare Steam Collieries (1891) Ltd., allowing opening of the Gorllwyn level in 1891. By 1896, No.1 pit employed 1,128, while renamed Nantmelyn now Bwllfa No.2 employed an additional 231. In 1907, the company took over the mineral rights to the old Powell's pit (also known as Pwll Troedrhiwllech and Cwmdare Pit), opened By Thomas Powell 1851, which it reopened as Bwllfa No.3. Like many mines, the company lost some of its workforce during
World War I, but by the end of 1918 this had recovered to: 1,054 at No.1; 931 at No.2/new drift No.4; 423 at No.3. Due to its ease of access, in 1922 the first electric powered coal cutting machines to be used in the
South Wales coalfield were installed at Bwllfa No.3. By 1923, producing both
ironstone and
steam coal: • No.1: employed 1,166 men producing from the Gorllwyn, Two Feet Nine, Four, Six and Nine Feet, Four Feet Upper and Lower, Yard and Seven Feet seams • No.2: employed 388 producing from the Yard, Gellideg and the New seams. A further 147 men were employed on the surface, shared with No.4 • No.3: employed 690 producing from Seven Feet, Lower Yard, Gellideg and the New seams • No.4: employed 202 producing on the New drift, and 139 producing on the Gorllwyn level Taken over by the Bwllfa and Cwmaman Coal Co. in 1928, part of Welsh Associated Collieries, in 1935 WAC merged its mining investments with those of
Powell Duffryn. The new company decided to cease production from No.3, which became a ventilation shaft. Post
World War II, by the time of nationalisation under the
National Coal Board, Powell Duffryn had also ceased production at No.1, equipping it as a ventilation shaft and pumping station. Coal was now only raised from No.2 and No.4, with a total below and above ground workforce of 572. ==Housing and amenities==