590 



GAS, COAL 



fluid which is condensed in the gas-pipo b, and in its prolongation from the gasholder, 

 runs off into the vessel A; and therefore the latter must bo laid so low that tin- siid 

 tube may have the requisite declivity. A straight stopcock may also be attached to 

 the side over the bottom, to draw off any sediment. 



1050 



The governor Although the gasholder is, to a certain extent, a regulator of 

 pressure, yet it is difficult, by its action alone, to maintain a pressure so steady and 

 uniform as that required for the supply of gas 

 consumers. It would be difficult, if not impossible, 

 to alter the pressure upon the mains frequently 

 during a single night, as is now usually done in 

 towns with a large number of street lamps, with- 

 out the intervention of an apparatus termed a 

 governor. The governor, which occupies a position 

 'between the gasholder and supply mains, is a 

 miniature gasholder A (see Jigs. 1052, 1053, and 

 1054, which represent Mr. Wright's improved 

 governor), the interior of which, however, is nearly 

 filled by the concentric inlet and outlet pipes B 

 and c. Immediately over the mouth of the inlet 

 pipe, and depending from tho roof of the inn'-r 

 cylinder, is a parabolic piston i>, which hang.s 

 within the contracted mouth of the inlet pipe c. 

 The interior cylinder is counterpoised by tho lover 

 and weights E E. Now, when tho pressure of tfas 

 in this small holder increases that is, when the flow of gas through tho inlet pipe 

 exceeds that escaping from the outlet the inner cylinder rises ; but, in doing so, it 

 carries with it the parabolic piston D, and thus contracts the orifice of tho inkt. ami 

 consequently diminishes tho ingress of gas. In this way, by adjusting the wiuhts 

 attached to the lever of the governor, and by always maintaining a pressure in tho 

 gasholder greater than is required in tho mains, the gas can bo delivered from tho 

 governor at any required pressure. In hilly towns, such as Bristol, Bath, Edinburgh, 

 &c., it is necessary to employ governors at different stages of elevation in order to 

 produce a tolerably uniform pressure in the different districts. Tho necessity for this 

 will be obvious when it is stated that a difference of level of 30 feet affects the pressure 

 of the gas in the mains to tho extent of ^ths of an inch of water. 



The gaa mains. The pressure by which tho motion of tho gas is maintained in tho 



