Steam-raising system

A steam-raising system comprising a boiler having (a) a passageway for water and/or steam, (b) an inlet to the passageway through which water is introduced continuously for given periods when the boiler is in use, (c) a heater to heat the passageway, and (d) an outlet from the passageway from which steam emerges continuously as water is introduced through the inlet, the system further comprising a pump connected by a flow-path to the said inlet to pump water thereto along the said flow-path and flow control means in the said flow-path, wherein the flow control means comprise a plurality of lines which constitute a part of the flow-path, which are connected between the pump and boiler in parallel with one another, and which are independently openable to enable the amount of water delivered to the boiler to be varied, each of the said lines comprises a shut-off valve and a flow regulator which maintains a constant flow through the line substantially independently of the pressures upstream of its inlet and downstream of its outlet, temperature monitoring means are provided downstream of the boiler to monitor the temperature of the steam output of the boiler, control means are connected to the temperature monitoring means and the shut-off valves to control operation of those valves in dependence upon an output from the temperature monitoring means, and the control means are such as to close each of the said lines at a predetermined temperature below that at which it opens that line, to provide a hysteresis range between the closing and opening temperatures.