| 摘要 |
<p>A proportional flow control valve comprises a directional control valve having a valve spool, a servo actuator or servo means for operating said directional control valve, and manual override means for operating the valve spool. The servo means comprises a movable ram or piston for moving the valve spool to thereby operate the directional control valve and the ram has a pair of equally sized piston areas connected thereto. The servo actuator also comprises a pilot valve having a null position and is selectively operable to apply fluid alternately to either of said piston areas to effect ram and valve spool movement in one direction or another from a null position. Means including a proportional electromagnetic device such as a proportional solenoid or force motor are provided for selectively operating the pilot valve. Feedback means are connected between the ram and the pilot valve to maintain the ram and the valve spool in a position wherein they are moved. Orifice means are connected between the pilot valve and the piston areas for relieving fluid pressure on one piston area when fluid pressure is being applied to the other piston area. The orifice means also serve to relieve the fluid pressure on both piston areas whenever the signal to the proportional solenoid is zero and the pilot valve is in null position to thereby prevent ram movement. Biasing means are provided on the valve spool for maintaining the ram and the valve spool in null position whenever the proportional solenoid signal is zero. The biasing means exert a force on the valve spool which is less than the force exerted by fluid being applied to a ram area whenever an electric signal is applied to the proportional solenoid. The override means are manually operable to move the valve spool by means of a mechanical linkage to effect manual operation of the directional control valve.</p> |
