Installation direction of high-temperature and high-pressure stop valves

There is a saying that under high temperature and pressure, with high inflow and low outflow, it is easier to ensure a good seal

It is said that the valve stem cannot withstand such high force. Under high-pressure conditions, when the valve is fully closed and the maximum differential pressure is reached, it becomes impossible to choose a larger diameter for the valve stem due to the low inlet pressure.

The high-pressure steam flow channel features a high inlet and low outlet, facilitating valve closure

For high temperature, high pressure, and large diameter applications, use a high inlet and low outlet design

High in and low out means that when the stop valve is opened, the medium flows within the S-shaped flow channel of the valve, in the direction of the valve, from above the valve disc to below it. Since the flow channel is in an horizontal S-shape, with the upward-curving part being considered “high” and the downward-curving part being “low”, if the medium flows from the upward-curving part to the downward-curving part, it is referred to as “high in, low out”. When the nominal diameter of the globe valve is DN≤200mm and PN≤25MPa, the “low in, high out” configuration is usually used, that is, the medium flows from below the valve disc to above it. Then why are high-inlet and low-outlet designs used for globe valves with DN>200 mm and PN>4.0 MPa? The disadvantage of allowing the medium to enter from below the valve core is that the driving torque required to operate the valve is higher, at approximately 1.05~1.08 times that when the medium enters from above. The axial force on the valve stem is also greater, making it prone to bending. These disadvantages become particularly evident as the nominal diameter and pressure increase, significantly affecting the proper functioning of the valve; therefore, a low-inlet and high-outlet design cannot be used in such cases. For this reason, the method of allowing the medium to enter from below is generally only suitable for small-diameter globe valves (DN50 and below); for globe valves with a diameter of DN200 or more, the method of allowing the medium to flow in from above is used. Electric globe valves generally allow the medium to enter from above. The disadvantages of the medium entering from above are exactly the opposite of those of entering from below. When DN is greater than 200 mm, a high-inlet/low-outlet design is used. The valve disc of this type of stop valve has a double-disc structure; since the flow rate increases when the diameter exceeds 200 mm, the pressure per unit area becomes very high. If a low-inlet/high-outlet design were used, a large counterforce would be required to ensure sealing, which would necessitate a larger valve stem. Additionally, the use of a lever handle or a worm gear with high torque would increase the volume of the valve and its production cost, with poor results as well. High inlet and low outlet pressure helps with sealing (the medium’s own pressure enhances the sealing effect after it is closed), but it is more difficult to open it as the pressure of the medium has to be overcome. “It facilitates an airtight seal; the medium pressure ensures a tighter airtight seal of the valve, and the stress conditions on the valve stem are improved.

High temperature and high pressure should mainly be of this kind, right?