缸体执行机构
Cylinder Actuators
空气或燃气缸体执行机构包括单动或双动，由机械弹簧或气动力实现故障开启或关闭等各种类型。空气缸体执行机构的局限性在于机械弹簧的局限性和要求推力不超过75,000磅。空气缸体执行机构所采用的机械弹簧可以达到20,000磅的推力，及最大14英寸的冲程限制，主要取决于所需要的输出推力。
Air or gas cylinder actuators include single or
double acting, fail open or closed by mechanical spring or pneumatic force.
They can be manufactured to accommodate any length stroke. The limitations
of air cylinder actuators are mechanical spring limits and thrust requirements
in excess of 75,000 Ibs. Mechanical springs used with air cylinders can
be sized for up to 20,000 Ibs. of thrust and have a stroke limit of about
14" max. depending on thrust output required.
对于有些无法采用机械弹簧的应用场合，可以配置气动弹簧，以储备足够实现故障安全功能的气源压力。大于25,000磅的推力要求可以通过配置标准镗孔的缸体执行机构来实现，在此假定现场气源压力最小为80
PSIG。在25,000磅至75,000磅之间的推理要求可以通过对现场气源进行增压或加强，使其具有更高的工作压力来满足缸体执行机构的要求，并储存在当地的高压气罐内。
In applications where mechanical springs can not
be used, a pneumatic spring provided with stored air pressure is capable
of providing a fail safe mode. Thrust requirements up to 25,000 Ibs. can
be accommodated with standard bore size cylinders assuming minimum 80
PSIG field air supply. Thrust requirements between 25,000 Ibs. and 75,000
Ibs. can be accommodated by boosting or intensifying field air pressure
to a higher working pressure for the cylinder and stored locally in a
high pressure air tank.
对于超过75,000磅的推力要求，液动系统会更加适合，也更加经济。缸体执行机构可以配置针对紧急状态下的手动过载装置，阀门驱动，故障安全功能和其它附件。
Hydraulic systems are better suited and more economical
for thrust requirements over 75,000 Ibs. Cylinder actuators can be provided
with manual overrides for emergency valve actuation, fail safe mode and
other accessories.
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隔膜执行机构
Diaphragm Actuators
隔膜执行机构适用于：双动(气压开启或关闭)，直接作用(气压关闭，机械弹簧开启)或反向作用(机械弹簧关闭，气压开启)。
Diaphragm actuators available are: double acting
(air pressure required open or close), direct acting (air pressure required
to close, mechanical spring to open) or reverse acting (mechanical spring
to close, air pressure required to open).
这是一种很简单也很经济的执行机构，但是应用的局限性也比较大。第一种局限在于冲程，对于大多数制造商来说，4英寸就是最大的冲程。这种局限性使得隔膜执行机构只能适用于通径DN100以下的闸阀和更小通径的截止阀。第二种局限性在于输出推力，这是无法为我们的不平衡旋塞截止阀选择这种执行机构的主要原因。大多数制造商可以提供面积达到200平方英寸的隔膜，但是，可用于执行机构的最大气源压力却在递减。大多数主要制造商提供的大面积隔膜的最大气源压力小于45
PSIG，因此限制了推力的输出。作为选配件，可提供手动过载手轮。
This very simple and very economical actuator
has application limitations. The first limitation is stroke; a 4"
stroke is the longest available from most manufacturers. This limits adaptable
valve size to gate valves 4" and smaller and globe valves in smaller
sizes. The second limitation is output thrust, this is the major constraint
in selecting this type of actuator for use with our unbalanced plug globe
valves. Most manufacturers can provide diaphragm areas up to 200 square
inches, however, maximum air pressure allowed for actuation decreases.
Maximum air pressures are as low as 45 PSIG for large area diaphragms
available from most major manufacturers thus limiting thrust output. Manual
override handwheels are available as an option.
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