Book - School of Science and Technology

306 Fuels, storage and handlingabcdef(a) Remote reading dial(b) Capillary(c) Anti-sludge unit(d) Tank bottom(e) Tank boss(f) Transmitter boxFigure 11.4 Oil tank contents gaugeHeaters. In the case of heavy oils, grades F and G, it is necessary to provide means ofmaintaining a suitable minimum temperature in storage, see Table 11.4, either by pipecoils or by electrical heaters. These are commonly of very simple construction andprovided with a coarse control of temperature.Outlet valve. For isolation, the outlet from each tank must be provided with a simple andreliable stop valve.HandlingThe treatment required to handle the flow of oil between storage and the point ofutilisation, and the associated equipment, varies greatly with the grade to be used.Necessary in all cases is an oil filter, which needs no further comment, and a fire valvemounted preferably externally, but always as near as possible, to the oil pipe entry to theboiler house.In its crudest form, a fire valve consists of a lever type isolator, heavily weighted, whichis kept open by a taut wire stretched across the boiler house and has a fusible link of lowmelting-point alloy over the oil burner with a hand operated release/test point at theboiler house door. Such devices are almost useless since they rely for operation upon theflexibility of the wire which, inevitably, becomes corroded or deformed where it passesover pulleys and, in any event, is rarely if ever tested for operation. It is current practice toprovide a much superior system where the weight-closed valve is kept open by a solenoidoperated catch, current to the circuit being maintained through a heat sensitive device(thermal fuse) mounted above the burner. Alarm bell or other contacts are easily added tosuch a circuit which inherently `fails safe'.