In August 1926, the London, Midland and Scottish Railway equipped four-cylinder 4-6-0 locomotive no. 5908 of the Claughton Class with Caprotti valve gear and poppet valves. Following trials, nine more were rebuilt in 1928 with Caprotti valve gear, poppet valves and larger boilers, and also in 1928 ten others of the same class were given the larger boiler but retained the Walschaerts valve gear and piston valves with which this class was originally fitted, to enable comparisons to be made between the two types of valve gear. Later that year, no. 5908 was also given a larger boiler. It was found that the Caprotti-fitted locomotives were more economical on coal and water than those with Walschaerts valve gear, but it was later found that some of the losses of the Walschaerts locomotives was due to leakage of steam past the valve heads, where a single wide ring was used. New piston valves having several narrow rings were fitted to one locomotive, and it was then found that the Walschaerts valve gear could be just as economical as the Caprotti, but with considerably less cost of fitment. No more Claughtons were fitted with Caprotti valve gear, and the ten locomotives were withdrawn in 1935–36.
On the London and North Eastern Railway (LNER), two 4-6-0 locomotives of LNER Class B3 were rebuilt with Caprotti valve gear in 1929, followed by a further two in 1938–39. These locomotives also had four cylinders, and the poppet valves were mounted vertically, two at each end of each cylinder. One of the first pair of locomotives was rebuilt again with Walschaerts valve gear in 1943, but the other three ran with Caprotti valve gear until withdrawal in 1946–47.
Although more expensive to manufacture than its rivals, this improved Caprotti valve gear is considerably more efficient than any other. Benefits include much of the mechanism being enclosed thus leading to reduced wear and tear from the harsh steam locomotive environment and completely independent control of admission and exhaust. The restored Duke of Gloucester, with its flaws eliminated, has proved the concept.