The damper regulator will control the pressure of steam, closing the damper when the pressure is raised beyond the desired point and opening the damper when the pressure falls below that point. By removing the weight on the lever, different degrees of pressure can be kept up. The regulator should be allowed to control the drafts without interference. Examine the water glass often to see that the _water line_ is at the proper height. If lower than normal open the supply pipe until the water runs in and stands at the proper level. It is best when no water stands in the glass, nor shows at the bottom of the try-cock, to quickly dump the grate and do not put water into the boiler again until it is cooled off. If there is one or more shut-off valves on the main or return pipes, before starting a fire see that one line of piping at least (main and return) is open to circulate the steam. =To Control Radiators.=--When it is desired to shut off steam from any radiator (if the regular radiator valves are used), close the valve _tight_, and when it is turned on see that the valve is _wide open_. A valve partly turned off will cause the radiator to fill with water. This rule applies only to one-pipe heating systems. =The Air Valves.=--If little keyed air valves (sometimes called “pet-cocks”) are used, follow generally the same directions as outlined for hot-water radiators on page 49--only, of course, in releasing the air from the radiator open the valve with the key provided and close it just as soon as the steam unmixed with air comes through the nose of the valve. If “automatic” air valves are used they must be carefully adjusted by the steam-fitter and then left to operate without undue interference. =End of the Season.=--At the close of the heating season fill the steam boiler with water to the safety valve and let it thus stand through the summer. Also thoroughly clean all the fire and flue surfaces of the boiler and at the opening of the next season withdraw the water and refill with fresh water to the water line, starting the boiler as before. It is advisable to have a competent steam-fitter blow off the boiler under pressure and thus give the inside a thorough cleaning when the boiler is first set up and ready for fire. A low-pressure boiler, using good water, rarely needs blowing off after it is once cleaned at time of setting up. THE RIGHT CHIMNEY FLUE The area of the flue should never be less than 8 inches in diameter if round, or 8 by 8 inches if square--unless for a very small heating boiler or tank heater. Nine or 10 inches round, or 8 by 12 rectangular is a good average size. The flue should generally have a little more area than that of the connecting smoke pipes. Draft force depends very much on the height of the flue.