Do stop valves also have high in and low out?

Yes, check valves also come in those with high inlet and low outlet.

Why are stop valves designed with the inlet at a higher level than the outlet? Stop valves are of the forced-sealing type; therefore, when the valve is closed, pressure must be applied to the valve disc in order to ensure that the sealing surfaces do not leak. When the medium enters the valve from below the valve disc, the resistance that the operating force must overcome consists of the friction between the valve stem and the packing, as well as the thrust generated by the pressure of the medium. The force required to close the valve is greater than that needed to open it; therefore, the diameter of the valve stem must be large enough, otherwise the valve stem may bend, a condition known as \"low inlet, high outlet\". In recent years, since the emergence of self-sealing valves, the flow direction of media in globe valves has changed to enter the valve chamber from above the valve disc, that is, from high to low. At this time, under the action of medium pressure, the force required to close the valve is low, while the force required to open it is high; accordingly, the diameter of the valve stem can be reduced. At the same time, under the influence of the medium, this type of valve is also more airtight. Therefore, when installing a stop valve, it is necessary to follow the flow direction indicator on the valve.

It seems that learning* is very necessary; many concepts change as technology evolves!

I’ve learned that… if there is a large pressure difference, and the valve is closed, higher requirements are placed on the sealing of the valve stem; poor quality can lead to leaks. I haven’t used self-sealing valves yet, but their sealing performance must be good, right? :)

I seem to have seen somewhere that for large-diameter valves, it is better to use a high inlet and a low outlet; the pressure of the medium helps to make it easier to close the valve. In the past, when the inlet was low and the outlet was high, it was more difficult to close the valve. Large-diameter or high-pressure globe valves are designed with the inlet at the top and the outlet at the bottom because the valve disc is too large while the valve stem is thin; relying solely on the valve stem to exert pressure is not sufficient, which can lead to internal leakage. Check valves that allow flow in one direction only are usually designed with double valve discs (also known as balanced valve discs). There are two reasons for this design: one is to prevent excessive pressure differences from occurring when the valve is opened or closed. Secondly, taking into account the stiffness of the valve, a medium flow structure with high inlet and low outlet is adopted; when the valve is closed, self-sealing is achieved in both the upper and lower directions. Moreover, the higher the pressure, the better the sealing effect.

It is true that large-diameter stop valves follow the principle of high inlet and low outlet.

Why does the force required to open the valve decrease after high inlet and low outlet conditions?

No, why can a thinner valve stem be chosen after switching to high-inflow and low-outflow operation? What are the advantages of using this self-sealing type?