Principles for selecting globe valves

A globe valve refers to a valve in which the closing element (disc) moves along the centerline of the valve seat. According to the movement of the valve disc, the change in the valve seat opening is directly proportional to the valve disc stroke. Due to the relatively short opening or closing stroke of the valve stem and the highly reliable cut-off function, as well as the proportional relationship between the change of the valve seat opening and the stroke of the valve disc, this type of valve is very suitable for regulating flow. Therefore, this type of electric globe valve is very suitable for use as a cut-off or regulating and throttling device.

The selection principle of shut-off valves is:
1. Globe valves should be selected on pipelines or devices with high temperature and high pressure media. Such as thermal power plants, nuclear power plants, and high-temperature and high-pressure pipelines in petrochemical systems.
On pipelines with less strict requirements for flow resistance on electric shut-off valve pipelines. That is, places where pressure loss is not considered much.
3. Small valves can choose needle valves, instrument valves, sampling valves, pressure gauge valves, etc.
4. There is flow regulation or pressure regulation, but the accuracy of regulation is not high, and the diameter of the pipeline is relatively small. For example, on pipelines with a nominal diameter of ≤ 50mm, it is recommended to choose.
5. Small and large fertilizers in synthetic industrial production should use high-pressure angle globe valves or high-pressure angle throttle valves with a nominal pressure of PN160, a nominal pressure of 16MPa, or PN320, a nominal pressure of 32MPa.
6. In the production of alumina by Bayer process, in the desilication workshop and easily coking pipelines, it is easy to choose DC electric globe valves or DC throttle valves with separate valve bodies, removable valve seats, and hard alloy sealing pairs.
In urban construction, for water supply and heating projects, for pipelines with a smaller nominal diameter, cut-off, balance valves, or plunger valves can be used, such as on pipelines with a nominal diameter less than 150mm.
The most obvious advantage is that during the opening and closing process, the friction between the electric globe valve disc and the valve body sealing surface is smaller than that of the gate valve, so it is wear-resistant. The opening height is generally only 1/4 of the diameter of the valve seat channel, so it is much smaller than a gate valve. Usually, there is only one sealing surface on the valve body and disc, so the manufacturing process is relatively good and easy to maintain. Nominal pressure or pressure level: PN1.0-16.0MPa, ANSI Class150-900, JIS10-20K, nominal diameter or diameter: DN10-500, NPS 1/2-36 "Connection method: flange, butt welding, thread, etc. Applicable temperature: -196 ℃~700 ℃ Drive method: pneumatic, electric, hydraulic, gas-liquid linkage, valve body material: WCB, ZG1Cr18Ni9Ti, ZG1Cr18Ni12Mo2Ti, CF8 (304), CF3 (304L), CF8M (316), CF3M (316L), Ti. Different materials can be used for water and steam respectively. Various media such as oil, nitric acid, acetic acid, oxidizing media, urea, etc.

Design analysis of manual shut-off valve
The shut-off valve body is the main pressure bearing component of the valve and accommodates the closing element. The flow channel inside the shut-off valve is designed to have a smooth circular inner wall without sharp angles and edges, providing a smooth process flow that does not produce abnormal turbulence and noise. The flow channel itself must have a constant area to avoid any additional pressure loss and excessive flow velocity. Globe valves have two wide end connections, making the valve body suitable for almost every type of end connection, although the face-to-face dimensions are too long to accommodate a flange less structure (bolt connecting the valve body between two pipeline flanges is common in rotary valves). For globe valves, mismatched end connections are also acceptable.
The valve core of a globe valve is a closed element that is larger than the exact position (because the throttle valve is larger than the precisely open or closed position, but rather the valve core is a regulating element), which changes the flow rate of the valve according to its flow characteristics and position. A typical valve core consists of two key components: the valve core, which is the convex part of the regulating element; The valve seat ring is the concave part. The part where the valve core is inserted into the valve seat ring is called the valve core head, while the part that extends through the top of the globe valve is called the valve core rod. There are screws on the top of the valve core rod to fit with the first wheel mechanism. The main advantage of a monotonically seated valve core is its possibility of tight closure (in some cases, it can reach 0.01% better than the maximum flow rate of the valve). This situation is caused by the direct force of the manual manipulator acting on the surface of the support.
In manual globe valves, there are two sizes of valve cores: full valve core, which is the most commonly used and involves the area of the valve seat ring, which can pass through the maximum flow rate within the special size of the globe valve. On the other hand, when it is desired to throttle the valve to less than the rated flow rate of the valve of that size, a reduced diameter valve core is used. If using a full valve core, it is necessary to throttle and close the valve seat with a small increment, but this is difficult to obtain with a manual operator. The preferred method is to use a smaller valve seat diameter and a matching plug, which is called a reducing valve core.
The valve cap is an important component of the top workpiece and serves as a pressure bearing part to provide a cap or cover for the valve body. Once it is installed on the valve body, it is sealed by the valve cap or valve body gasket. He also uses a packing box to seal the valve core rod, which includes a series of packing rings, glands, or guide covers. Filler spacers and anti extrusion rings are used to prevent a small amount of leakage of process media into the atmosphere. The flange installed on top of the packing box is the gland flange, which is connected to the top of the valve cap with bolts. When the gland flange bolts are tightened, the packing is compressed and seals the valve stem and valve cap holes.
Maintaining the alignment between the valve core head and the valve seat ring is important for tight closure. To maintain this alignment, one of two guiding mechanisms can be used: a double top stem guide or a valve seat guide. The double top valve stem guide uses two closed fittings to guide at both ends of the packing box, keeping the hairstyle and valve seat ring concentric. These guides can be made of metal that is compatible with the plug as a whole to avoid metal scratches, and can also use elastomers or graphite liners. The structure of the two guides should be kept as far away as possible to avoid lateral movement caused by the action of process fluid on the valve core head. The guide, valve cap hole, and actuator stem must be maintained within the allowable deviation when closed to maintain a fit, which will result in smooth linear motion without restraint and splashing of liquid.
Another commonly used guide type for manual shut-off valves is the seat guide structure. The valve core rod here is supported by an upper guide (which functions like a packing gland). The outer diameter of the extended part of the valve core head serves as the second guiding surface to guide the valve seat. This means that the surface of the lower guide remains within the logistics layer, so the process medium is relatively clean. The lower part of the valve core head has an opening, which allows the flow of material to reach the valve seat through the valve core head during the valve seat opening process. Changing the size and shape of these openings will affect the reduction of flow rate and flow characteristics. Because the length between the upper and lower guides is at the maximum length, lateral plug movement caused by process flow is not a problem, and the allowable deviation required for this type of guide is not as strict as that of the double top stem guide. This structure reduces the chance of any vibration of the valve core during operation. When the valve core and valve seat are made of the same material, metal surface wear may occur during long-term or frequent operations. High temperatures can cause thermal expansion and fatigue.
The metal support surface of the valve core is designed to match the metal support surface of the valve seat ring, but its contact angle is slightly different. Under normal circumstances, the valve core has a larger angle than the taper of the valve seat ring. This annular mismatch ensures a narrow point of contact, where the axial force of all operators is only transmitted to a small part of the valve seat, thus obtaining the possibility of the strictest metal to metal contact closure. In most structures, the seat ring of a manual globe valve is threaded into the valve body. Another requirement is to use tools to rotate the valve seat ring within a limited space. There are also some drawbacks to threaded valve seats: firstly, in corrosive or harsh working conditions, the threads will be corroded, making disassembly difficult. Secondly, when aligning the valve core and valve seat, additional grinding steps are required to achieve the desired valve closure. Thirdly, in the presence of vibration, the valve seat ring cannot be held by the plug in the closed position because the valve seat ring may eventually loosen and cause leakage through the valve seat gasket or misalignment of the valve seat surface.
Some globe valves require bubble tight closure, which cannot be achieved with metal to metal sealing. To achieve these, an elastic body can be embedded in the valve seat ring. In this case, the valve seat ring is a two-part structure, with an elastic body embedded between the two halves. The surface of the metal plug is pressed against the soft support surface of the valve seat ring. If the surface of the valve core and valve seat ring is concentric, a double tight closure can be achieved. Some manufacturers have also achieved the same effect by embedding elastomers inside the valve core.