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A set of three photographs shows a needle valve in the fully-closed, mid-open, and fully-open positions (left-to-right): Needle valves are very common as manually-actuated valves used to control low flow rates of air or oil.
![valve stem tool valve stem tool](http://prfactorystore.com/wp-content/uploads/RKcvgOKg.jpg)
For this reason, this particular style of globe valve is called a stem-guided globe valve.Ī variation on the stem-guided globe valve design is the needle valve, where the plug is extremely small in diameter and usually fits well into the seat hole rather than merely sitting on top of it. The left-hand photo shows the valve body in the fully closed position, while the middle photo shows the valve half-open, and the right-hand photo shows the valve fully open:Īs you can see from these photographs, the valve plug is guided by the stem to maintain alignment with the centerline of the seat. A photograph of a small (2 inch) globe valve body appears here:Ī set of three photographs showing a cut-away Masoneilan model 21000 globe valve body illustrates just how the moving plug and stationary seat work together to throttle flow in a direct-acting globe valve. The globe valve design is one of the most popular sliding-stem valve designs used in throttling service. Fluid flows through a hole in the center of the seat, and is more or less restricted by the plug’s proximity to that hole. Globe valves restrict the flow of fluid by altering the distance between a movable plug and a stationary seat (in some cases, a pair of plugs and matching seats). Of course, a reverse-acting valve body would behave just the opposite: opening up as the stem is pushed in and closing off as the stem is drawn out. Conversely, a direct-acting valve shuts off (closes) when the stem is pushed into the body. Most sliding-stem control valves are direct acting, which means the valve opens up wider as the stem is drawn out of the body. Some examples of sliding-stem valve body designs are shown here:
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A sliding-stem valve body is one where the moving parts slide with a linear motion.