Careful examination should be made of the valves and pipe connections to see that they are efficient and properly applied. Many styles of valves are available, and only well known or well tested patterns should be allowed. Of air valves for steam radiators the simplest form is the "pet cock", a screw valve operated by hand (Fig. 61), but there are several forms of automatic valves on the market which will allow the escape of cold air from the pipes, but are instantly closed as soon as affected by the hot steam. This is done by the expansion of a metal part which closes the orifice. Radiators. The form of steam radiator in general use is the east iron radiator (Fig. 62). This consists of a series of loops connected at the bottom. The steam entering at one end forces the air out of the air valve placed about midway of the last section. The two end sections are of the same internal patterns as the others but are cast with legs.

Fig. 61. Air Valve.

Fig. 61. Air Valve.

Pipe radiators (Fig. 63) are often used and, where design is not an object, the use of circulation coils of piping may be permitted.