plug. The outlet pipe is concentric to the inlet pipe and rises some distance above the level of the water. The holder is provided with an annular float of such buoyancy that when the tank is charged to the proper water-line it rises, carrying with it the suspended parabolic plug, and, supposing all the weights on the top of the holder to be removed, the holder would ascend to its full limit, and in so doing would cause the parabolic plug to completely fill the orifice in the inlet pipe, and would thus shut off the

supply of gas, when, of course, the governor would not give any pressure; but supposing we required to give a. certain pressure on the district, say, fifteen tenths; then on placing weights equivalent to that amount on the top of the holder, the holder would descend, and with it the conical plug which would open the orifice at the top of the inlet main to the extent requisite to allow sufficient gas to give the pressure required to escape, and no matter what variations may take place in the pressure at the works, or the amount of gas consumed on the district, the same pressure is rigidly maintained by the governor at its outlet; for in the event, say, of a sudden draught on the main owing to an increased consumption, the pressure in the main would be reduced, and as the governor and holder communicate by means of the outlet pipe with the district main, this reduced pressure would cause the governor holder to descend; in so doing the parabolic plug would also descend and open the gas-way more, thus causing more gas to pass through the valve opening, and in this way maintain the pressure at that originally intended; on the other hand, should the

FIG. 40.

consumption on the district slacken, then the pressure in the main would increase and back up as far as the governor, where it would lift up the holder, which would at the same time lift up the suspended plug higher into its seating, thus reducing the gas-way, and consequently the pressure on the district. Of course, the governor is not intended to control the initial pressure which is required for supplying the district, the pressure required at any particular time being regulated by the addition or taking off weights from the crown of the holder.

As previously remarked, the holder is buoyed up by means of an annular float, the same result can be attained by attaching a chain to the crown of the holder on the outside; the chain passes over one or two pulleys, and terminates in a rod which carries weights sufficient to counterbalance the holder, and by taking weights off this rod, the latter operate in the same manner as if they were placed on the top of the holder.

The valve which increases or decreases the area of the gas aperture is made in the form of a parabola, on account of the latter form of valve producing the effect desired within a shorter range, and also by reason of its being more delicate and reliable in its action.

66

The parabola should be made twice its diameter in length, and of weight sufficient to resist, without oscillation or blinking, whatever pressure may be exerted against it by the inflowing gas" (Newbigging).

66

be

Now all forms of governors of the kind just described, and which are classed as cone valve governors," possess one great disadvantage, viz., they are all liable to oscillate when variations occur in the inlet pressure, which may caused either by the bringing into action gas-holders of different weights, or by the cupping and uncupping of telescopic holders. The variations of the inlet pressure acting upon the base of the valve sets the latter moving,

N

this is communicated to the bell of the governor, with the consequence that "blinking" ensues, which is very annoying. Another cause of governors not being steady is by having the gas communications of a much larger area than is really required. In order to overcome these defects various devices have been designed, one of the most successful being that of reducing the size of the pipe communicating with the holder, and which, in the majority of cases, need not be more than about an inch in diameter,

FIG. 41.

and also by arranging that the inlet pressure acting on the valve is balanced by a similar pressure acting on the other side of the valve. In the governor patented by Messrs. J. and J. Braddock the last-mentioned result is arrived at in the following manner, fig. 41 :

"The gas enters the base of the governor, passing over the valve and downwards into the valve chamber to the outlet. Fixed. to the centre of the crown of the holder is a chamber like an inverted canister with the cover removed, which is always sealed in the water in the tank, and does not communicate in any. way with the governor holder, and is of exactly the same sectional area as the base of the valve. This compensating chamber communicates directly with the inlet por-tion of the governor, and is subjected to the same pressure as the valve. Now supposing the inlet pressure is suddenly increased, this acting upon the valve tends to. push it downwards, and so increase the gas-way, but as the same pressure exerts itself upon the same extent of area against the crown of the holder inside the com

pensating chamber, and tends to raise it, a state of equilibrium is produced, and the position of the valve kept constant" (Herring).

Mr. C. Hunt, the late Examiner in Gas Manufacture to the City Guilds of London Institute, has invented a governor which works on a different principle to those just described, by adapting the ordinary throttle

valve to the purpose of a gover

nor.

This method possesses the advantage that a gas-holder scarcely larger than the main is only required.

The construction of the appa ratus is as follows, fig. 42:

Within the supply main leading from the works to the district, a disc or throttle is accurately balanced on two small steel centres, the lever by which the disc is moved being also inside the main, and attached to the centre of the disc. A small vertical pipe places the holder in communication with the main, and serves to inclose the lever which is attached to the disc and to the crown of the holder, and also conveys the gas into the latter.

FIG. 42.

The governor of Messrs. W. and B. Cowan, shown in fig. 43, possesses many distinguishing features. In place of the parabolic valve of the ordinary cone governor a hollow cylindrical valve is employed, which is closed at the bottom but open at the top. Around the sides of this valve a series of conical ports are formed, and this arrange

ment permits the governor to be in perfect action while only passing an extremely small volume of gas.

A further advantage with this form of valve is, that by reason of its being accurately fitted in its surrounding seating it is only capable of a free vertical motion, whereas the parabolic valve, being suspended, is free to move sideways. In order to counteract the influence of the inlet pressure on the base of the valve the following arrangement is employed:

On the crown of the governor holder an annular tank is fixed, and into this latter a bell or holder, suspended from, and fixed to, the cross-bar of the governor guides, dips. The diameter of this bell corresponds with the diameter of the valve below, and forms, with the annular tank, a water lute, which incloses an area equal to that of the valve base. The hollow rod which suspends the valve also conveys the gas from below the valve base, or from the inlet side of the governor, to the interior of the chamber inclosed by the water lute, and exerts the same pressure above the bell of the governor. In this way the inlet pressure is exactly, equalized on each side of the valve. The gas is supplied to the governor bell from the outlet side by means of the centre tube, which terminates a little above the water-line, and through which the valve rod passes.

In addition to improving the construction of the governor itself, Messrs. Cowan have made a decided advance in the method of working the same, i.e., by the employment of water in place of weights for the purpose of putting on and taking off the pressure; by this arrangement the pressure is imperceptibly changed, whereas in the old way of regulation, by weights, even when carefully performed by increasing and decreasing the pressure very gradually, the change of pressure was frequently observable on the district. The water-loading apparatus for increasing the pressure, and Cowan's patent stationary syphon for the removal of