The several proportions are such that a slight over-pressure is maintained above the piston to give the valve, at all times, a tendency to close. This over-pressure should be but slight, and to regulate it at will there is (besides the leak around the piston) a separate steam admission above the piston, regulated by the plug, C.
Depending on the fit of the piston, this plug is opened more or less, or entirely closed, when valve is first put in operation, and then locked in that position.
Ordinarily the construction of this valve demands the application of a screw-spindle to actuate it; it is also made in angle form and can be placed with spindle upward or horizontal. In all positions, globe, inverted and angle valves, steam must always enter above the disc, viz., in the direction of the arrows.
Fig. 633.
The operation by lever is demanded when a valve is used as a quick emergency shut-off, either by hand or in connection with automatic appliance of governor, electrical cut-off or auxiliary, steam, air or hydraulic cylinder.
The valve itself is of the balanced form, except that in this valve the spindle carries at the bottom a small piston or sleeve, F, shown in the figure. The valve is locked open by moving hand lever up till the catch on same engages with the lever, G, supported on the upright bar.
The valve being then open, steam pressure acts on the area of the piston, F, with continuous downward force, which will cause the valve to close as soon as the latch is released. Thus, by connecting the rod on the outer end of lever, G, with a hand lever, at any desired location, the operation is had without effort and promptly.
A pressure reducing valve is shown in outline and a side view in Figs. [633] and [634]; this is in effect a (Mason) pump pressure regulator and it is applicable for fire, tank, elevator, air and water works pumps, or any class of pumping machinery where it is necessary to maintain a constant pressure. The regulator may be quickly adjusted to any pressure desired by turning the key as shown in Fig. [633].
The especial feature of this regulator is that the pressure chamber into which the water enters is entirely removed and separate from the steam and all working parts.