Trunnion Ball Valves – Pros and Cons
Trunnion ball valves are vital devices to control and shut-off the flow of fluid (gas, oil, steam, water, etc) at a petrochemical plant. The advantages are: valve is highly effective, efficient, flexible, easy to maintain and reliable; it is also highly flexible because it can be easily adapted to different operating environments: throttle controls the amount of fluid flow while maintaining constant pressure: this makes it easier to perform precise measurements on the amount of fluid to be shut off: it requires only one screw for adjusting the position of the throttle. The only downside is: it does not possess effective throttling and regulating capabilities. The disadvantages are as follows: valve is poorly regulating and throttling abilities; it is not suited for closed loop systems; when the valve is forced open (usually by high pressure), the partly exposed seat corrodes because of excessive heat: this can occur because the piston fails to fully cover the ring; the rotating movement of the ring will result in erosion of the ring surface. This can cause a gradual erosion of the ring material, causing a failure of the valve in future operations.
There are many types of ball valves available today; most of them can be fitted in the same manner: they are suitable for most applications, including pipeline shut-offs. It is important to determine which type of valve is best suited for the application before purchasing it.
A trunnion-type valve is a valve having two rotating plates that move parallel to each other while the stationary plate is fixed on top of the wall of the valve chamber. It is widely used in chemical processing. It is usually made from stainless steel, or a metal alloy of high hardness. Usually there is one ball or cylinder positioned above the other in the mechanism and it contains an o-ring to stop the movement of the plates if it slips.
Hydraulic ball valves are used for high volume applications. They are similar to a trunnion ball but the mechanism consists of an annular ring instead of rotating plates. The ring is fixed above the chamber wall and a hydraulic cylinder placed on its side. The ring pushes the piston down by pulling a lever or spring, causing the cylinder to move up and down.
The main disadvantage of this type of valve is that it is more prone to wear and tear, because the ring may wear out sooner than the piston. It can also be difficult to adjust the valve’s position to avoid the formation of erosion.
The ring piston is made from a special material such as brass or steel. The thickness and composition of this material depend on the size of the ring as well as on the pressure needed for the piston to operate smoothly. Some are designed with two chambers and some even have three chambers. The piston must be of appropriate size for the system because it needs to be inserted into the valve chamber at the same time. They are also designed so that the piston moves from side to side instead of going straight forward and back, which gives better flexibility. Some manufacturers use a mechanism that prevents the piston from sliding when the ring moves up or down, because this can damage the ring.