This subclass covers general aspects of, or methods for, preheating or accumulating feed water. All devices in a power plant or a steam boiler for heating water in liquid form, like economisers or water preheaters and accumulating water for preheating purposes, controlling and regulating the water level in said water accumulators, feed-water supply like automatic water feeding and controlling methods are covered. Furthermore safety feed water supply and arrangements of feed water pumps are also covered.

Water heaters in general are classified in F24H. Generation of steam or vapour is classified in F22B, devices and methods for superheating steam in F22G. Steam engine plants where engine aspects predominate are classified in F01K, domestic central heating systems using steam are classified in F24D, heat exchange or heat transfer in general is classified in F28.

General aspects and constructional features of devices or heat exchangers for heating water normally beyond the boiling point in order to improve the boiler's efficiency arranged in a flow path up stream of an evaporator. This group covers also economisers and preheaters with water tube arranged in the boiler furnace, in fire tubes or in flue ways, with water tubes arranged outside the boiler furnace and heated for example in a separate heat exchanger. Furthermore also water and air preheating systems, combinations of exhaust-steam and smoke-gas water preheater and preheaters incorporating thermal de-aeration are covered.

Heat exchangers and types thereof are classified in F28C and F28D, details of heat-exchange and heat-transfer apparatus are classified in F28F.

Accumulators and storage vessels for water which is heated in an economiser arranged within the combustion chamber or combined with steam accumulators and thereby heated by steam or connected directly to boilers by water conduits. Water accumulators with preheated water specially adapted for locomotives and control devices are also covered by this group.

Devices and methods for controlling the supply of feed water and the feed water level using intermediate compartments, pivoting buckets, receptacles outside of the boiler and devices with float actuated valves, responsive to thermal expansion and contraction, with electric switches. Also regulators with varying the speed or delivery pressure of feed pumps and automatic feed-control systems are covered by said group.

Documents concerning measuring volume, volume flow, mass flow or liquid level are classified in G01F and documents concerning level control in general in G05D 9/00.

Devices in for promoting or enhancing water circulation like saddles, deflecting plates, Venturi arrangements, injectors for water or steam, rotary devices like for example pumps, said devices also specially adapted for locomotive boilers. Control devises of said devices are also covered by said group.

Pumps in general are classified in F04B, F04C, F04D and F04F

All other aspects of feed water supply, which are not covered by the other main groups, like for example emergency feed water supply, arrangements of feed water cleaning, when the water is cleaned between condenser and boiler and arrangements of feed water pumps

Pumps in general are classified in F04B, F04C, F04D and F04F

Only feed water supply devices and methods for which there is no entry in the main group F22D 7/00 are to be classified in F22D 11/00.