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Heating Ventilating Air Conditioning Guide 1939 Overfeed Inclined Grate Stokers In general the combustion principle is similar to the flat grate stoker but this stoker (Fig. 3) is provided with rocking grates set on an incline to advance the fuel during combustion. Also this type is provided with an ash plate where ash is accumulated and from which it is dumped periodi cally. This type of stoker is suitable for all types of coking fuels but preferably for those of low volatile content. Its grate action has the tendency to keep the fuel bed well broken up thereby allowing for free .Chapter 11 Automatic Fuel Burning Equipment the volatile gases are released, are mixed with air, and pass through the fie where they are burned. The ash may be continuously discharged as the small stoker or may be accumulated on a dump plate and periodiin., discharged. This stoker requires no arch as it automatically pro vides for the combustion of the volatile gases. Fig. 3. Overfeed Inclined Grate Stoker passage of air. Because of its- agitating effect on the fuel it is not so desirable for badly clinkering coals. Furthermore, it should usually be provided with a front arch to care for the volatile gases. Underfeed Side Cleaning Stokers In this type (Fig. 4), the fuel is introduced at the front of the furnace to one or more retorts, is advanced away from the retort, as combustion progresses, while finally the ash is disposed of at the sides. This type of stoker is suitable for all coking coals while in the smaller sizes it is suitable for small sizes of anthracites. In this type of stoker the fuel is delivered to a retort beneath the fire and is raised into the fire. During this process 208 Underfeed Rear Cleaning Stokers This type of stoker accomplishes combustion in much the same manner as the side cleaning type, but consists of several retorts placed side by side and filling up the furnace width, while the ash disposal is at the rear. In principle, its operation is the same as, the side cleaning underfeed. Stokers also may be classified according to their size based upon coal med rates. The following classification has been made by the United States Department of Commerce in cooperation with the Stoker Manu facturers' Association. Class 1. Up to and including 60 lb of coal per hour. Class 2. 60 to 100 lb of- coal per hour. 209