Why are double valve cores used in stop valves

In general, for a globe valve, the flow direction of the medium is from the channel at the lower left side of the diagram to the channel at the upper right side, that is, from low to high. The illustrated stop valve features a reverse design with high inlet and low outlet. Its purpose and reason is to achieve a lower opening and closing torque under high pressure.

You are right, but you haven’t explained why a dual spool is used

This post was last edited by wangsir85 on 2018-8-27 at 16:58. I. To understand the reason for having two valve cores, one must first comprehend the principle behind each of them: 1. First of all, this type of structure is called pilot-operated. The medium flows from the right end to the left end, that is, from a higher level to a lower one. Used in large-diameter, high-pressure applications. 2. With a single spool, the medium flows from the left end to the right end, that is, from low to high. Used for small-diameter, low-pressure applications. II. Reasons for using dual valve cores: 1. If a single valve core is used in high-pressure, large-diameter applications, the valve stem will have to bear the thrust from the entire flow channel. In such high-pressure, large-diameter situations, this thrust is quite significant, and it falls on the valve stem to bear it. As a result, the valve stem needs to be large enough; otherwise, it will get damaged. Additionally, when closing or opening the valve, it is necessary to overcome this entire thrust, which means that the torque required is also very high. Therefore, a single spool is not used. 2. By using a dual-core valve, when the medium flows from high to low, the valve stem can be designed to be smaller, and the opening torque is also low. In particular, the torque required to close or open the valve is smaller, as when closing or opening the valve stem only needs to overcome the thrust exerted by the small valve seat above; once it is opened, the pressure difference decreases, and as the valve stem is moved further upward, the torque further decreases. The same applies when closing the valve, with respect to the larger valve seat below. Since the medium flows from a higher level to a lower one, it can be approximated as if the valve stem does not need to withstand the thrust exerted by the medium; thus, the valve stem can be designed to be much smaller.

With a pressure rating of 900BL, the pressure difference before and after the valve is high, resulting in large torque required for opening and closing. The use of dual valve cores is intended to reduce this torque and facilitate operation: first activate 3.0.20 and then 3.0.1； Close the valves by first closing 3.0.1 and then 3.0.20

I’ve learned more about this, thank you

The explanation on the 4th floor was very thorough. Judging from the diagram, this valve should not be for high pressure; designing a valve for medium or low pressure in such a complex manner is unnecessary

The common type of stop valve has fluid entering from the bottom and exiting from the top, depending on the diameter and pressure. The image above shows high pressure at lower levels; this phenomenon is generally observed only under high pressure or with large diameters. When turning it on, it first increases slightly before increasing further. In simple terms, it is to reduce the pressure difference and protect the valve internals.

Another point is that this approach can improve the sealing level while keeping the same actuator. Doing this should allow reaching V-level.