Design Analysis of Lifting Stem Ball Valve/track Ball Valve

The valve body of a Special Valve is the main pressure-bearing part of the valve and houses the closing element. The flow passage in the Special Valve is designed to have a smooth arc inner wall without sharp corners and sharp edges, which can provide a smooth process flow without abnormal turbulence and noise. The flow passage itself must have a constant area to avoid any additional pressure loss and excessive flow rate. Special Valve have wide end connections, so the valve body can be adapted to almost every end connection, although its face-to-face dimension is too long to accommodate flangeless structures (bolting the valve body between two pipeline flanges, which is common in rotary valves). For Special Valve, mismatched end connections are also possible.

The valve plug of a Special Valve is a closing element larger than the exact position (because the Throttle Valve is larger than the position of just opening or closing, but the valve plug is more like a regulating element), which allows the valve to change the flow rate according to the flow characteristics and the position of the valve. The typical valve plug consists of two key parts: the valve plug, which is the male part of the regulating element; and the valve seat ring, which is the female part. The part of the valve plug that is inserted into the seat ring is called the valve plug head, while the part that protrudes through the top of the Special Valve is called the valve plug stem. The top of the valve plug stem is threaded to cooperate with the first wheel mechanism. The main advantage of the monotonic seat valve plug is its tight closing possibility (in some cases, it can reach better than 0.01% of the maximum flow of the valve). This situation is caused by the manual operator's force acting directly on the seat surface.
There are two sizes of valve plugs in the Lifting Stem Ball Valve/Track Ball Valve: full valve plug, which is commonly used and refers to the area of the valve seat ring that can pass the maximum flow in a Special Valve size. On the other hand, when it is desired to throttle the valve to a lesser flow than the rated flow of the valve of that size, a reduced diameter valve plug is used. If a full valve plug is used, the valve seat must be throttled closed in smaller increments, which is difficult to obtain with a manual operator. The preferred method is to use a small seat diameter and a matching plug, which is called a reduced diameter valve plug.
The bonnet is an important component of the top workpiece and provides a cap or cover for the valve body as a pressure-containing part. Once it is installed on the valve body, it is sealed by the bonnet or body gasket. It also seals the Valve Stem with a stuffing box, which includes a series of packing rings, glands or guides. Packing spacers and anti-extrusion rings are used to prevent small leaks of process media to the atmosphere. Mounted on the stuffing box is the gland flange, which is bolted to the top of the bonnet. When the gland flange bolts are tightened, the packing is compressed and seals the valve stem and bonnet holes.
Keeping the valve head and seat ring aligned is important for tight shutoff. To maintain this alignment, one of two guiding mechanisms can be used: double top stem guides or seat guides. Double top stem guides use two closure fittings at each end of the stuffing box to guide the head and seat ring concentrically. These guides can be made of a metal that is compatible with the plug to avoid metal galling, or they can use elastomer or graphite bushings. The two guides should be constructed as far apart as possible to avoid lateral movement caused by the process fluid acting on the valve head. The guide, bonnet bore and actuating stem must be kept within tolerance when closed to maintain a fit that will result in smooth linear motion without binding and splashing of fluid.
Another common type of guiding for rising stem/orbital ball valves is the seat guided arrangement. Here the plug stem is supported by an upper guide (which acts like a gland). The outside diameter of the extended portion of the plug head acts as a second guide surface to guide the seat. This means that the lower guide surface remains within the flow layer, so the process media is cleaner. The lower portion of the plug head has openings that allow flow movement through the plug head to the seat during the seat opening process. Changing the size and shape of these openings affects the reduced flow and flow characteristics. Because the length between the upper and lower guides is at a maximum length, lateral plug movement due to process flow is not a problem, and the tolerances required for this type of guide are not as tight as those for the double top stem guide. This arrangement reduces the chance of any vibration of the plug during operation. When the valve plug and valve seat are made of the same material, metal surface wear may occur during long-term or frequent operation. High temperatures can cause thermal expansion and wear.
The metal seat surface of the valve plug is designed to match the metal seat surface of the valve seat ring, but the contact angle is slightly different. Under normal circumstances, the valve plug has a larger taper angle than the valve seat ring. This annular mismatch ensures a narrow point of contact, so that the entire axial force of the operator is transmitted to only a small part of the valve seat, thereby obtaining the possibility of a tight closure of metal-to-metal contact. In most structures, the valve seat ring of the Lifting Stem Ball Valve/track Ball Valve is screwed into the valve body. Again, the valve seat ring is required to be rotated with a tool in a limited space. There are also certain disadvantages to the threaded valve seat: first, the threads will corrode under corrosive or harsh working conditions, making disassembly difficult. Second, additional grinding is required when aligning the valve plug and the valve seat.