| 摘要 |
<p>A valve includes a device for reducing the force required beyond cracking, thereby reducing the size of actuating equipment. A balance chamber includes two effective diameters. A smaller diameter is operative during cracking, in order to maintain positive control of the valve. Later, a larger balance diameter is effective, in order to reduce the actuation forces required beyond the cracking position. A pilot valve is opened during initial actuation. Once the pilot valve is fully opened, a main valve is opened. A dual-diameter balance chamber is effective, during initial opening of the main valve, to require substantial opening forces. Then, when the main valve reaches a predetermined distance from its seat, the second effective diameter increases the balance area to reduce the valve actuating forces required.</p> |
