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Description: |
| Abstract:
I have attained all that is desirable in an equilibrium-valve Without introducing any new defects or materially increasing the cost of manufacture of the valve or of the engine to which it is to be applied.
My balanced valve is peculiarly adapted for ready compensation for wear, and does not require any peculiar adaptation of the cylinder or steam-chest, and hence can be applied to engines already in use.
There are two principal classes of balanced slide-valves: First, pressure-plate valves-flat slides in which the pressure of the steam is taken of the back of the valve by means of the steam-chest cover or some special rigid plate or hood introduced in the steam-chest for the purpose; and, second, piston valves, Where the valve, usually cylindrical for convenience of manufacture, but which may be theoretically of any shape, moves steam-tight in a casing, as a piston moves in a cylinder, and the steam, being forbidden access to its sides, and acting in opposite directions against its ends, causes a balance of pressures.
A common defect of valves of the first class is that they make no provision for balancing pressure from the cylinder due to steam already admitted, or to compression after exhaust closure, acting outward on the area of the valve which covers the port, and which varies in intensity from that of the exhaust up to or even above that in the boiler. They cannot lift off their seats to relieve pressure from such source, being held down by the pressure-plate or hood. Excessive pressure from this cause, due to water entrapped within the cylinder by the closing of the valve, is liable to cause destructive accident. Sometimes the pressure plate or hood is not fastened to the valve-seat, the object of leaving it loose being to allow it to rise with the valve and so relieve pressure from within; but the area of the back of the plate or hood is necessarily many times greater than the area of the port through which the internal pressure acts, so that it is practically immovable, and the provision for allowing it to rise fails to accomplish any good result. It simply renders the parts more liable to become displaced.
Valves of the second class-piston-valves have the ports extended quite around, so that any pressure from any source is certainly balanced g but to secure sufficient portage the valve must be made very large relatively to a flat slide of equal opening, involving increased friction, weight, wear, etc., and as the valve wears smaller While its casing wears larger it rapidly grows leaky and must be replaced.
Piston valves are peculiarly subject to objection in case of water in the cylinder. Such valves cannot possibly leave their seats.
I have combined the advantages of valves of the two classes-hooded slide-valves and piston-valves-and have eliminated their defects. While having the general form of a hooded Valve, my valve is really a piston valve, made in such shape as to secure large port opening Without excessive Weight, While the form is easy to refit in case of leakage from Wear. I combine with it a special provision for relieving back pressure.
Claims:
1. The flat cylinder-face A, balanced slide valve B, having flat faces and beveled edges, a corresponding hood, C, and an inclosing steam chest, allowing the steam to apply on the exterior of the hood, all combined and arranged to serve as herein specified.
2. The plane cylinder-face A, having ports, the hood C, having plane interior surfaces, beveled, as shown, and provided with grooves c, and also with ports for relief-openings through into the steam-chest, in combination with the flat valve B, having beveled edges, and with relief-valves E, all arranged for ljoint operation, as and for the purpose herein specified.
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