About manual stop valve design

The shut-off valve body is the main pressure-bearing part of the valve and houses the closing element. The flow passages in the shut-off valve are designed to have a smooth rounded inner wall without sharp corners and sharp edges, thus providing a smooth process flow that does not create abnormal turbulence and noise. The flow channels themselves must have a constant area to avoid any additional pressure loss and excessive flow rates. The shut-off valve has a wider two end connections so that the valve body is suitable for almost every type of end connection, although its face-to-face dimension is too long to accommodate a flangeless structure (bolting the valve between two line flanges Body, which is common in rotary valves). Mismatched end connections are also possible with stop valves. The shut-off valve spool is a closed element (because the throttle valve is larger than the position just opened or closed, but rather the valve spool is the adjusting element) than the exact position, which allows the valve to follow the flow characteristics (which can be equal percentage , Linear or quick-open type, see section 2.2 for details) and the position of the valve to change the flow rate. A typical spool consists of two key components: the spool, which is the male part of the adjustment element; the seat ring, which is the female part. The part where the valve plug is inserted into the seat ring is called the valve plug head and the part protruding through the top of the stop valve is called the valve plug lever. The top of the valve rod on the car with threaded buckle to match the first round of institutions. The main advantage of a monotonic seat is its tight shut-off (in some cases up to 0.01% of the maximum flow of the valve). This situation is caused by the force of the manual manipulator acting directly on the bearing surface. In manual shut-off valves, however, there are two sizes of spools: Full spool, which is the most commonly used and relates to the area of ​​the seat ring that can pass the maximum flow through a special size of the shut-off valve. On the other hand, a reduced diameter spool is used when it is desired to throttle the valve to a lower nominal flow rate than the size of the valve. If full spooling is used, the seat must be throttled off with small increments, but this is difficult to obtain with hand controls. The preferred approach is to use a small seat diameter and a matching tap, which he calls a reduced diameter spool. The bonnet is an important element of the top work piece and provides a cap or cap for the valve body as a pressured part. Once it is mounted on the valve body, it is sealed by a bonnet or body gasket. He also seals the plug stem with a stuffing box that contains a series of packing rings, glands or guide lids. Filler spacer and anti-extrusion ring, to prevent the process medium to a small amount of leakage to the atmosphere. Mounted on top of 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 the stem and bonnet holes are sealed. Maintaining the valve plug head and seat ring centered is important for tight shutoff. To maintain this alignment, one of two guide mechanisms can be used: a double top stem guide or seat guide. The double top stem guide uses two closure fittings to guide both ends of the stuffing box - keeping the hairstyle concentric with the seat ring (Figure 3.19). These guides can be monolithically made of a metal that is compatible with the cock to avoid metal scratching, and elastomers or graphite bushings can also be used. The structure of both guides should be as far apart as possible to avoid lateral movement caused by the process fluid on the valve plug head. The guides, bonnet holes, and actuator stem must be held within tolerance to maintain a fit that will result in smooth and linear movement of unconstrained and spilled liquid. Another type of manual shut-off valve is the guide of seat-oriented structure. Here the spool is supported by an upper guide (it acts like a packing gland). The outer diameter of the plug head extension serves as the second guide surface to guide the valve seat (Figure 3.20). This means that the lower director surface remains within the logistical layer, so the process media is cleaner. The lower portion of the valve head has an opening that moves the flow through the valve head to the valve seat during valve seat opening. Changing the size and shape of these openings will affect flow reduction and flow characteristics. Because the length between the upper and lower guides is at the maximum length, lateral cocks due to process streams are not a problem, and the tolerances required for this type of guide are not unlike the double top stem guide The device is as strict. This structure reduces the chances of any vibrations in the spool during operation. When the valve plug and seat are made of the same material, metal surface wear may occur over long or frequent operations. High temperatures can cause thermal expansion and puffing. The metal seat surface of the valve plug is designed to match the metal seat surface of the seat ring but with a slightly different contact angle. Normally, the spool has a larger angle than the seat ring taper. This ring-shaped mismatch assures a narrow point of contact, with the entire operator's axial force being transmitted only to a small portion of the valve seat, thus giving the possibility of the closest metal-to-metal contact closure. In most constructions, the seat ring of the manual shutoff valve is threaded into the valve body. Again it is required to use a tool to rotate the seat ring in a limited space. There are also some disadvantages with threaded seats: First, the threads are corroded in corrosive or harsh conditions, making disassembly difficult. Second, when aligning the spool and seat, Additional grinding steps to get the required valve closure. Thirdly, in the presence of vibration, the seat ring can not be retained by the cock in the closed position because the seat ring may eventually become loose and leak through the seat gasket or misalign the seat surface. Some shut-off valves require close shut-off of the bubble, which metal-to-metal seal is unattainable. To accomplish this, an elastomer can be embedded in the seat ring. In this case, the seat ring is a two-part structure with an elastomer inserted between the two halves (Figure 3.21). Metal cock surface pressure to the seat ring soft bearing surface, such as the spool and seat ring surface is concentric, you can get double close. Some manufacturers have the same effect by embedding elastomers in the valve plug

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