1. Why can’t double sealed valves be used as shut-off valves?
The advantage of the double seat valve core is its force balance structure, which allows for a large pressure difference. However, its prominent disadvantage is that the two sealing surfaces cannot make good contact at the same time, resulting in large leakage. If it is artificially and forcibly used in cutting situations, the effect is obviously not good, even if many improvements have been made to it (such as double sealed sleeve valves), it is not advisable.

2. What type of straight stroke control valve has poor anti blocking performance, while angle stroke valve has good anti blocking performance?
The valve core of a straight stroke valve is vertically throttled, while the medium flows in and out horizontally. The flow channel inside the valve chamber inevitably turns and twists, making the valve’s flow path quite complex (shaped like an inverted “S”). In this way, there are many dead zones that provide space for the precipitation of the medium, which, over time, can cause blockages. The direction of throttling of the angle stroke valve is the horizontal direction, where the medium flows in and out horizontally, easily carrying away unclean media. At the same time, the flow path is simple and there is little space for the medium to settle, so the angle stroke valve has good anti blocking performance.

3. Why is the straight stroke regulating valve stem thinner?
It involves a simple mechanical principle: high sliding friction and low rolling friction. The stem of a straight stroke valve moves up and down, and if the packing is slightly compressed, it will tightly wrap the stem, resulting in a large backlash. For this reason, the valve stem is designed to be very small, and PTFE packing with low friction coefficient is commonly used as the packing to reduce backlash. However, the problem with this is that if the valve stem is thin, it is easy to bend and the packing life is short. The best way to solve this problem is to use a travel valve stem, which is a regulating valve with angular stroke. Its stem is 2-3 times thicker than a straight stroke stem, and it uses graphite packing with long service life. The stem stiffness is good, the packing life is long, and its friction torque is small and the backlash is small.

4. Why is the cut-off pressure difference of angular stroke valves relatively large?
The cutting pressure difference of angular stroke valves is relatively large because the combined force generated by the medium on the valve core or valve plate has a very small torque on the rotating shaft, so it can withstand a large pressure difference.