3 DrumsLoads of steam

Design

Possibly the best Stuart boiler for larger engines, indications are that it is based on the Cheddar models Pegasus boiler. The design, similar to the Yarrow design is called a Blackstaff,The main difference is the use of straight connecting pipes in the Yarrow and coiled pipes in the Blackstaff. The Yarrow is more common in full size use where the many straight tube allow for fast water circulation, for models the curved tube design allow for many less tubes tu get a similar effect. It consists of 3 drums mounted 1 at the top above the heat and one each side. The top drum is connected to both the lower drums in an inverted V formation. There are several pipes connecting the drums, each is coiled to increase surface area. The extensive surface are in contact with the flame results in very fast run up to pressure. Water is heated in the coiled tubes and rises into the head drum, this suck water down to the feeder drums via the straight pipes. This means that strong circulating currents form, ensuring that all the water is subjected to the heat in the coiled pipes. Heat source for the Mendip was by a choice of 3 methods, a gas burner was available as well as a grate for use with wood or coal. A small dome is fitted to the top for drier steam.