sentences:  Portable engines were very simple with no gearing connected to the road wheels, no tanks were fitted, water was drawn to the engine from a barrel placed alongside, and the majority had single cylinders; however compound versions were produced.Charles Burrell & Sons produced portables in a range of sizes, these were rated by the company in NHP.Around 670 portable engines were completed by the firm; however by the turn of the 20th century production of portables had slowed to a crawl as the company became more occupied with production of self-moving steam engines, and the final portable engine was sold in 1908.