Heat exchange su are usually cleaned by circulating 10% hydrochloric acid solution. A pump is connected to the feed inlet to the evaporator and solution return is by gravity via the brine d into an open acid tank from which the pump draws the solution. The single effect vertical shown in Figure 3 is still in common use. It evaporator operates with a vapour pressure between 1.34 and 1.48 bar and steam for the heating coils is supplied directly from the boiler. The initial cost for such an evaporator is relatively low, it is also compact and thereby space saving. The shell and dome the evaporator is made of good-quality close-grained cast iron and the heating coils made of solid drawn copper Mountings provided are vapour outlet valve, are steam inlet, coil drain valve, feed check valve, low-down valve, brine ejector, safety valve, gauge glass with fittings, salinometer cock and a compound pressure gauge. In the diagram, a reducing orifice fitting is shown on the steam inlet. Its purpose is to reduce the pressure of steam entering an evaporator shell in the event of failure of a heating coil.