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Based on the movement path of the valve stem, control valves can be divided into straight-stroke control valves and angle-stroke control valves. In straight-stroke control valves, the valve stem moves back and forth in a straight line; typical examples include single-seat control valves, double-seat control valves, sleeve control valves, three-way control valves, and angle-type control valves； Angle-type control valves generally perform reciprocating rotational motion within a 90-degree range; typical examples include control butterfly valves, control ball valves, eccentric rotary valves (cam-deflected valves), and plug valves. Straight-stroke control valves and angle-stroke control valves differ significantly in terms of their performance due to the structural differences between them. Let’s briefly compare the advantages and disadvantages of each type in terms of performance: 1. Comparison of Kv values: The flow path of straight-stroke valves is complex, with an S-shaped configuration, which results in high flow resistance and low flow capacity; as a result, their flow coefficient Kv value is low. The medium flow path of angle-type control valves is simple, resulting in low flow resistance, high flow capacity, and a large Kv value (their Kv value is approximately 1.5 to 3 times higher than that of linear-type control valves). 2. Comparison of anti-clogging functions: It is still due to the complex flow path of the medium in straight-stroke valves, which results in large vortex dead zones; this allows the medium to settle around the throttle opening, leading to clogging and preventing the valve core from closing properly or opening at all. In angle-seat valves, the medium flows essentially in a straight path, making it difficult for deposits to form; as a result, they have excellent anti-clogging properties, which is why they are said to have good \"self-cleaning\" capabilities. 3. Weight comparison The S-shaped flow path of the medium results in a relatively complex internal structure of the control valve; its dimensions are large, and this complexity also affects the valve’s external shape. Due to its larger external dimensions, the valve has a greater weight as well. Angle stroke valves have a simple flow path, as well as simple internal and external structures; they are also small in size, which results in a lower weight. 4. Comparison of valve stem sealing performance: In straight-stroke valves, the valve core moves up and down, which makes it easy for the medium to escape; as a result, their valve stem sealing performance is poor. Due to the rotational movement of the valve stem in angle-type valves, it is difficult for the medium to leak out. Moreover, packing with better sealing properties can be used, which increases the sealing performance of angle-type valves by 2-3 times compared to straight-stroke valves. Under the pressure exerted by the gland, the packing deforms and tightly compresses the valve stem, generating a frictional force F1 = jf, where j represents the packing compression force and f is the coefficient of friction. For straight-stroke valves, the total force acting on the valve stem is F = F1 + F2; therefore, an actuator with high output force is required. For diagonal-stroke valves, M = Mt + Mf, where Mt is the unbalanced torque and Mf is the frictional torque. Taking an eccentric rotary valve as an example, M = Mt + Mf = FeX + F1r, where X is the distance between the center of the valve core and the center of the shaft, and R is the radius of the valve core’s shaft. Since X is small and r is also not large, the total torque is not significant, allowing for the use of an actuator with a lower output torque. 5. Overcoming pressure difference issues The unbalanced structure of single-seal valves in straight-stroke valves means that, during flow, the pressure difference can easily push the valve core open; therefore, a low pressure difference is sufficient ； In a rotary angle valve, the rotation of the valve core results in an unbalanced torque equal to \"force * lever arm\"; since the lever arm is small, the torque is low, which allows for a high pressure difference (as high as the pressure P1 before the valve). It is clear from the above aspects that straight-stroke control valves and angle-stroke control valves each have their own advantages and disadvantages; when making a selection, we can take these aspects into consideration.