Now, the Parmelee sprinkler takes a considerable time to open - over two minutes usually - owing to the length of the solder seam, and the mass of metal near it; yet concerning it, Atkinson says: - " The Parmelee sprinkler is shown, by the tests made by Woodbury, to be about the least sensitive head on the list, and the least in capacity of discharge; and yet the whole eiperienco with the Parmelee sprinklers has been a success, the discharge of water has sufficed, and we hare no record of a fire getting away from
If such is the fact with the least sensitive sprinkler, what result may we not expect from the later forms of sensitive types of sprinklers? More than 160,000 of the Parmelee have been used in the States, and several mills have been fitted with them in England.
The sprinkler invented in 1881 by Frederick Grinnell showed a marked advance in many details, and soon superseded the Parmelee. Each sprinkler is calculated to supply an area of 100 it. The valve, a leaden disc affiled to the centre of a larger disc of brass, is held up against the valve orifice by a system of two curved levers, the lower of which is secured by fusible solder at its lowest point to a light metal frame (Figs. 40-43). The Take-seat is itself made elastic by the device of filing it in the centre of a diaphragm of thin, bard metal, perforated for that purpose; and the pressure of the water upon the diaphragm keeps it tight against the valve. The larger disc attached to the valve-disc serves as a deflector. When the solder is melted, the levers fly apart, and the valve and deflector drop about 1/2 in., leaving space for the water to escape. It dashes against the disc, which is notched, and slightly dished at its edges, and is then deflected upwards in spray towards the ceiling, whence it falls to the floor.
Grinnell sprinkler, open.
When the sprinkler has worked, it requires to be re-soldered. It seldom requires more than 15 seconds to elapse before the levers fly under the influence of a direct flame. With an ascending hot column of air, the sprinkler seldom waits for a whole minute before it works. In the very short time that has elapsed since this invention was introduced, it has entirely superseded the Parmelee. There are now more than 300,000 of these in the States, and more than 30,000 in Great Britain, chiefly in the Lancashire cotton district, but also in a number of factories and warehouses in London.
The success of the sealed Parmelee and the sensitive Grinnell sprinkler have been such as to arouse the emulation of inventors to produce other forms of sprinkler. In the States the sprinklers of Harris, Brown, Bishop, Burritt, Rutherburg, and Walworth are more or less known, though in less extensive use than either the Parmelee or Grinnell forms. In the Harris, Brown, and Burritt (sensitive) forms the valve is held up by a soldering which holds up the valve-stem somewhat as in Harrison's original plan. Jn Ruthenburg's sprinkler a pair of levers, clamped by a bit of fusible tube, hold up a rubber ball. In the Walworth sprinkler the valve-stem is held up by a cam worked by a lever which is either soldered to the body of the sprinkler, or else clamped by an oval link of fusible metal. This latter device is good in so far as it enables the sprinkler, after working, to be closed up again by merely slipping on another ring without the need for skilled labour or the removal of the sprinkler from the ceiling; but the oval ring of alloy is liable to distension and fracture, as the alloy is somewhat brittle, and will not stand much tensile stress.
Indeed, the question of alloys must be considered from several points of view, as the most fusible alloy does not necessarily possess the greatest tenacity or the most sharply defined melting point. A piece of Grinnell solder was found to fuse at 165° F.; it was tough and even flexible; whilst a Walworth link which melted at 161° F., was not nearly so tough. Professor Guthrie's "eutectic" alloy, which fuses at 159° F., was not found to be so tough or to have so sharply defined a melting point as some alloys of slightly higher melting point. Of course it is an advantage, from the point of view of sensitiveness, to work with an alloy that has a very low melting point; but it mast not be so low as to risk being melted with the ordinary temperatures at the ceiling of a gas-lit room. Obviously, an electrically-lighted mill may be fitted with sprinklers that are more sensitive than those which can be used in gas-lit 'mills. Conversely, in drying houses and store-rooms, special solders with higher melting points are preferred.
Grinnell sprinkler in position.
Progress in the perfection of the automatic sprinkler has not been confined to the other side of the Atlantic, and in addition to the American forms, there are several English forms well worthy of notice. In one of these, the invention of Sidney Smirke, architect, a valve is used resembling the valve of the Victor system presently to be explained, and the water when admitted by the valve is forced into the narrow annular space between two metal dishes, the upper one of which is capable of adjustment.
Ingenious sprinklers have been invented by Philip Jolin, engineer, of Bristol (Figs. 43, 44.) The form which promises best success has a lead-topped ball valve held up against the supply orifice by a pair of springy metal levers, which are clamped below by a fusible clamp. This clamp, which is readily replaced after the sprinkler has worked, is of an ingenious form, in which the solder is relieved of all direct tearing stress. It consists of a button, made in two parts, soldered at the edges right and left, and admitting the ends of the levers by an aperture which passes from top to bottom. This bottom is protected beneath a divided cone, which serves partly as a deflector for the water, partly as a protector to the clamping button, partly as a collector of the ascending hot air. When the lever opens, the valve ball drops a short distance and operates as a deflector. In another form (Fig. 44), a small truncated cone of alloy holds up the deflecting ball to its seat. In yet another form, the levers are held together by a double link of brass (Fig. 45), the two parte of which are prevented from parting by a wedge of alloy, subjected only to compressing and shearing stresses, not to tensile