The check value is also called a cut-off valve. Due to the small friction between the sealing surfaces during the opening and closing process, it is relatively durable, has a small opening height, is easy to manufacture, and is easy to maintain. It is not only suitable for medium and low pressure, but also for high pressure. For example, steam cast steel check values, especially bellows check values, are used in projects involving water, oil, steam, gas and other media. Since they are so widely used, this article analyzes its working principle in detail to help users understand and application.
How the globe valve works
Simply put, the principle of the check value is to use the valve stem torque to apply downward pressure to the sealing surface, and rely on the valve stem pressure to make the valve disc sealing surface and the valve seat sealing surface closely fit to prevent the inflow of the medium or to adjust the flow rate of the medium. . The opening and closing part of the check value is a cylindrical valve disc, the sealing surface is flat or conical, and the valve disc moves linearly along the center line of the fluid. The movement modes of the valve stem include the lifting rod type (the valve stem rises and falls, the handwheel does not rise and fall), and the lifting and rotating rod type (the handwheel and the valve stem rotate and rise together, and the nut is set on the valve body). The check value is a forced sealing valve, so when the valve is closed, pressure must be applied to the valve disc to force the sealing surface not to leak.
The closing principle of the check value is to rely on the pressure of the valve rod to make the valve disc sealing surface and the valve seat sealing surface closely fit to prevent the flow of media.
The check value only allows the medium to flow in one direction and is directional when installed. The structural length of the check value is larger than that of the gate valve. At the same time, the fluid resistance is large, and the sealing reliability is not strong during long-term operation.
Let’s give a vivid example of how to use the check value.
We assume that there is a pipe with a cover. Water flows in from the bottom of the pipe and flows out toward the pipe mouth. The cover of the outlet pipe is equivalent to the closing member of the check value. If you lift the pipe cover upward by hand, the water will flow out. Covering the pipe will stop the flow of water, which is equivalent to the working principle of a check value.
The check value rotates the handwheel to raise and lower the valve stem, driving the valve disc to move linearly parallel to the flow direction of the medium to achieve the purpose of opening and closing. The handwheel rotates clockwise, and the working medium enters through the channel below the valve disc. At this time, the applied sealing force must be equal to or greater than the sum of the necessary specific pressure generated on the sealing surface and the upward force of the medium.
When the check value is opened, when the opening height of the valve disc is 25% to 30% of the nominal diameter, the flow rate has reached the maximum, indicating that the valve has reached the fully open position. Therefore, the fully open position of the check value should be determined by the stroke of the valve disc.
Note: Application of check value
1. The check value only allows the medium to flow in one direction, and it must be directional when installed.
2. The function of the check value is either 0 or 1, either passing or blocking. In other words, the check value is only suitable for fully opening and fully closing, and adjustment and throttling are not recommended.
Extended reading of other parameters of check value
Nominal pressure or pressure level of check value: PN1.0-16.0MPa, ANSI CLASS150-900, JIS 10-20K, nominal diameter or diameter: DN10~500, NPS 1/2~36"
check value connection method: flange, butt welding, thread, etc. Applicable temperature: -196℃~700℃
check value driving mode: manual, bevel gear transmission, pneumatic, electric, hydraulic, gas-hydraulic linkage, electro-hydraulic linkage
Valve body material: WCB, ZG1Cr18Ni9Ti, ZG1Cr18Ni12Mo2Ti, CF8(304), CF3(304L), CF8M(316), CF3M(316L), Ti
The check values are made of different materials and can be applied to various media such as water, steam, oil, nitric acid, acetic acid, oxidizing media, urea, etc.