上工牌通用截止阀用途 Purpose of general globe valve

【上海精工阀门厂 技术资讯】
截止阀的启闭件是塞形的阀瓣。密封面圼平面或锥面。阀瓣沿流体的中心线作直线运动。阀杆的运动形式，有升降杆式（阀杆升降， 手轮不升降），也有升降旋转杆式（手轮与阀杆一起旋转升降，螺母设有阀体上）。截止只适用于全开和全关，不允许作调节和节流。

截止阀属于强制密封式阀门，所以在阀门关闭时，必须向阀瓣施加压力，以强制密封面不泄漏。当介质由阀瓣7、方进入阀门时， 操作力所需克服的阻力，是阀杆和填料的摩擦力由介质的压力所产生的推力，关阀门的力比开阀门的力大，所以阀杆的直径要大，否 则会产生阀杆顶弯的故障。近年来，从自密封的阀门出现以后，截止阀的介质流向就改由阀瓣上方进入阀腔，这时，在介质压力的作 用下，关阀门的力小，而开阀门的力大，阀杆的直径可以相应减小。同时，在介质作用下，这种形式的阀门也比较严密。我国阀门 的“三化组”曾规定，截止阀的流向，一律采用自上而下。

截止阀开启时。阀瓣的开启高度，为公称直径25%-30%时，流量已达到最大，表示阀门已达全开位置。所以截止阀的全开位置， 应由阀瓣的行程来决定。

The opening & closing part of stop valve is the piug-shape valve disc, its seal surface is plane or conical surface, and the valve disc moves in straight line around the center of liquid. The valvestem is divided into rising stem type （the stem lifts, but the handwheel doesni-t）and rising & rotary stem type（both the handwheel and the stem lift and rotate, and the valve body is equipped with the nuts）。 The valve is only applied to open and close fully, but not to adjust the flux.

The stop valve belongs to the compulsive seal valve, so when close the valve, must force on the valve disc to compulsively make the seal surface no leakage. When the medium flows into the valve form the lower part of valve disc, the resistance the operation must overcome is just the friction force of stem and packing, and the pushing force caused by the pressure of medium, and because the closing needs bigger force than the opening, the diameter of valve stem is bigger, or a bended trouble probably happens to the valve stem Recently, since the presence of self-seal valve, the medium of stop valve flows into the valve cavity form the upper part of disc instead of the past flow direction, and then, under the pressure of medium, the closing needs less force than the opening, so the diameter of stem is reduced accordingly. At the same time, the valve is quite sealed under the pressure of medium. It is ever stipulated by the valve three chemical-industry organizations in our nation that the flow direction of stop valve must be from up to down.

When the stop valve is opened, and the lift height of disc is 25% -30% as much as nominal diameter, the flux reaches the max, which shows that the valve is already opened fully. So the full-open position of stop valve should be decided by the stroke of disc.