Of late years these have attracted some attention among market growers, and many are now using them. The chief advantages appear to be that a boiler can be added to if necessary if more work is required from it. Each section is independent and can be bolted on to the others or taken away. They are considered to be very economical in fuel, they are easy to stoke and keep clean, and the cost of brickwork is saved in the setting. Being made of cast iron they are less liable to rust than the wrought-iron boilers are when fixed in a damp stokehole; and in the case of a section giving way, it can be easily replaced instead of the whole boiler being rendered useless as would be the case with a wrought-iron boiler. There are several kinds of sectional boilers now on the market, one of the best known being the "Robin Hood"of Messrs. Foster & Pearson (fig. 177), of which there are several patterns. Other makes are the "Mona" and "Anglian". The illustration (fig. 178) shows a type having a Sylphon automatic regulator by means of which the draught can be regulated. Automatic regulators, however, are not recommended for damp stokeholes, as the rust soon causes the working-parts to be out of repair.