Several common problems with control valves
Addtime：2023-06-17 From： View：461
When the double-seat control valve is operating in a small opening state, it is prone to oscillation.
Why can't the double-seat control valve be used at a small opening? This is determined by its valve seat structure. The double control valve has two valve cores, with the upper valve core being open and the lower valve core being closed. When the valve core of the control valve is open, the stability is better. Therefore, when the valve core of the double-seat control valve operates at a small opening range close to the closed state, the valve core will oscillate. Thus, in the selection of control valves, it is necessary to avoid using the double-seat control valve in the small opening range.
The valve core of the double-seat control valve has the advantage of a force-balancing structure, allowing for a wide range of pressure differences before and after the valve. However, since the two sealing surfaces cannot simultaneously make good contact, the leakage is significant, and it cannot effectively cut off the flow in the pipeline. Even though the sleeve modification has been added to the double-seat valve now, it still cannot overcome the limitations caused by its structural design.
3. Comparison of the anti-blocking performance between linear stroke control valves and angular stroke valves?
The valve core of a linear motion control valve moves vertically, while the fluid moves horizontally. The flow channel structure inside the valve chamber is not a straight-through type; it is generally in the shape of an S, thus forming many blind areas. Over time, the medium is prone to accumulate sediment in these blind areas, which can easily lead to blockage. In contrast, the valve core of an angular motion valve moves in a horizontal rotation, and the fluid also flows horizontally. Therefore, there are less blind areas, and the sediment is more likely to be carried away by the fluid. Thus, the anti-clogging performance of the linear motion control valve is much better than that of the angular motion valve.
4. What is the reason for the relatively thin valve stem of the linear motion control valve?
Due to the principle of greater sliding friction and smaller rolling friction. The valve stem of the linear stroke valve moves up and down, resulting in a large friction force. Therefore, the valve stem is designed to be slender and uses a fluorine-containing polytetrafluoroethylene packing with a low friction coefficient, all of which are aimed at minimizing the friction as much as possible. However, this has led to problems such as the valve stem being slender and thus prone to bending, and the short lifespan of the packing.
5. Is the shut-off pressure difference for the rotary valve relatively large?
Because the resultant force exerted by the medium on the valve core is very small, the torque generated by this force on the valve shaft is also very small. Therefore, it can withstand a large pressure difference, so the shut-off pressure difference of angle-travel type valves is relatively large.
6. Why should the shut-off valve be equipped with hard seals as much as possible?
In terms of the sealing effect alone, soft-sealing valves perform better than hard-sealing valves. However, soft-sealing valves have much poorer wear resistance and reliability compared to hard-sealing valves. Therefore, from the perspective of both leakage and reliability, hard-sealing cut-off valves are superior to soft-sealing cut-off valves. Nowadays, many cut-off valves use hard-fused wear-resistant alloys to significantly improve the sealing performance, which is sufficient to meet the requirements of the cut-off valves.
Why can't the double-seat control valve be used at a small opening? This is determined by its valve seat structure. The double control valve has two valve cores, with the upper valve core being open and the lower valve core being closed. When the valve core of the control valve is open, the stability is better. Therefore, when the valve core of the double-seat control valve operates at a small opening range close to the closed state, the valve core will oscillate. Thus, in the selection of control valves, it is necessary to avoid using the double-seat control valve in the small opening range.
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The valve core of the double-seat control valve has the advantage of a force-balancing structure, allowing for a wide range of pressure differences before and after the valve. However, since the two sealing surfaces cannot simultaneously make good contact, the leakage is significant, and it cannot effectively cut off the flow in the pipeline. Even though the sleeve modification has been added to the double-seat valve now, it still cannot overcome the limitations caused by its structural design.
3. Comparison of the anti-blocking performance between linear stroke control valves and angular stroke valves?
The valve core of a linear motion control valve moves vertically, while the fluid moves horizontally. The flow channel structure inside the valve chamber is not a straight-through type; it is generally in the shape of an S, thus forming many blind areas. Over time, the medium is prone to accumulate sediment in these blind areas, which can easily lead to blockage. In contrast, the valve core of an angular motion valve moves in a horizontal rotation, and the fluid also flows horizontally. Therefore, there are less blind areas, and the sediment is more likely to be carried away by the fluid. Thus, the anti-clogging performance of the linear motion control valve is much better than that of the angular motion valve.
4. What is the reason for the relatively thin valve stem of the linear motion control valve?
Due to the principle of greater sliding friction and smaller rolling friction. The valve stem of the linear stroke valve moves up and down, resulting in a large friction force. Therefore, the valve stem is designed to be slender and uses a fluorine-containing polytetrafluoroethylene packing with a low friction coefficient, all of which are aimed at minimizing the friction as much as possible. However, this has led to problems such as the valve stem being slender and thus prone to bending, and the short lifespan of the packing.
5. Is the shut-off pressure difference for the rotary valve relatively large?
Because the resultant force exerted by the medium on the valve core is very small, the torque generated by this force on the valve shaft is also very small. Therefore, it can withstand a large pressure difference, so the shut-off pressure difference of angle-travel type valves is relatively large.
6. Why should the shut-off valve be equipped with hard seals as much as possible?
In terms of the sealing effect alone, soft-sealing valves perform better than hard-sealing valves. However, soft-sealing valves have much poorer wear resistance and reliability compared to hard-sealing valves. Therefore, from the perspective of both leakage and reliability, hard-sealing cut-off valves are superior to soft-sealing cut-off valves. Nowadays, many cut-off valves use hard-fused wear-resistant alloys to significantly improve the sealing performance, which is sufficient to meet the requirements of the cut-off valves.