A distilling plant cannot maintain its full out-put unless it is supplied with dry steam at the designed pressure. The orifices supplied are designed to pass the proper amount of steam to ensure designed plant output with a pressure of about 5 psig above the orifice. Orifices should be inspected annually. An orifice should be measured and the reading compared with the figure stamped on the plate. If necessary, the orifice should be renewed.

If the steam pressure above the orifice varies, the source of trouble should be located and cor-rected. First the weight-loaded regulating valve and then the pressure reducing valve (if installed) should be checked to determine whether or not each valve is operating properly. If they are func-tioning properly and the pressure cannot be main-tained above the orifice, you may assume that an insufficient amount of steam is being supplied to the plant.

The auxiliary exhaust steam supply for the distilling plants, after passing through the regulating valve, is usually slightly superheated because of the pressure drop through the reduc-ing valve and orifice plate. A small amount of superheat has little or no effect on the operation or the scale formation; however, when live steam must be used, the installed desuperheater spray connection should be used to control the superheat. The water for desuperheating must be taken from the boiler feed system, preferably from the first-effect tube nest drain pump. Water for desuperheating must never be taken directly from the freshwater distilled by the distilling plant. Fluctuations in the first effect generating steam pressure and temperature cause fluctuations of pressure and temperature throughout the entire plant. With increased salinity of the distillate, the fluctuations may cause priming, as well as erratic water levels in the shells. These fluc-tuations may be eliminated by proper operation of automatic pressure regulators in the steam supply line.