Reciprocating Safety Valve.
It must be sufficiently obvious that when the gas holder is full, and the distillation of the gas continues going on, that unless a provision is made for conveying away the surplus gas, it must escape by bubbling up from underneath the gas holder. And should the gas holder happen to be enclosed within walls, the gas may by chance accumulate, so as to give rise to serious accidents.
As a remedy for this evil the manufacturers of coal gas have until very lately contented themselves with what is called a safety tube, adapted to the gas holder, by which, all the superfluous gas was carried away into the open air; or by leaving large apertures in the roof or upper part of the building, for the ready escape of the gas. By either of these devices the danger from the accumulation of waste gas, was in part only avoided, and instances might be named where dangerous consequences ensued from an accumulation of gas, in a confined atmosphere, in the vicinity of the upper part of the gas holder.
In some instances, indeed, recourse was had to the establishment of a communication between all the reservoirs and an auxiliary gas holder or gas holders, by means of a pipe furnished with an hydraulic valve; but this was an expensive arrangement which required personal superintendance, and depended, of course, for its efficiency on the integrity and good conduct of the servant employed.
Mr. Clegg has now, however, invented what has been termed the Reciprocating Safety Valve, which has a self-acting operation, and by which an exit for the surplus gas of any number of gas holders that may be in action is provided to an unlimited extent. A communication is established between all the gas holders and a waste pipe, which communication opens or closes by the action of the gas, as occasion requires, and which may be extended to any number of gas holders at a trifling cost.
The apparatus has now been adopted at the greater number of gas light establishments, and has been uniformly found most efficient in its operation. Fig. 9, [plate VI.], presents a perpendicular section of the apparatus; h, h, h, h, is a small vessel made of sheet iron, about eighteen inches in diameter, and twenty inches deep, closed at top and open at bottom. It is inverted into an outer air tight vessel, i, i, i, i, of double the height and rather greater diameter, which is filled with water to a certain height; D, is a pipe communicating with the gas holders that are in action; this pipe branches upwards through the bottom of the outer vessel, i, i, i, i, and reaches a little above the surface of the water in the outer vessel. E, is a small pipe, the upper extremity of which is sealed by means of an inverted sheet iron cup G, the edge of which is submersed under the surface of the water in the outer vessel, i, i, i, i. This pipe conveys the waste gas into the upper part of any chimney.
For let us suppose that the gas holders become overcharged; the gas must then acquire an increased density before the wooden curb of the gas holder G, fig. 7, [plate VI.],[45] at the lower extremity of the overcharged gas holder can begin to rise out of the water. But when the elasticity of the gas is thus far increasing, and before the curb can wholly emerge out of the water, the small vessel h, h, h, h, of the reciprocating safety valve, ascends, and consequently establishes a communication between the overcharged gas holder and the pipe D, of the reciprocating safety valve. The surplus gas thus passes into the waste pipe E, E, which had been before sealed by the inverted cup G, and is hence conveyed into the upper part of the chimney where it terminates, so that no accumulation of gas can ever take place above, or in the vicinity of any gas holder.
[45] Every gas holder ought to have a wooden curb at the bottom.
It must be obvious on the other hand, that when the gas in any of the gas holders has recovered its original density, the reciprocating safety valve will again be closed by the descending of the cup G.