(under subclass 397) Devices in which water is caused to pass from the surface of the boiler through the conduits.
SEE OR SEARCH THIS CLASS, SUBCLASS:
91, and 202, for a water tube circuit with sediment trap.
389, for "skimmers".
399, for combination of surface and bottom outlets to a trapped circuit.
415, for surface exit circulating circuits without a trap in the circuit, but having a forced circulation by means of a mechanical pump, with feed water introduced into the circuit.
