What is the principle of dry gas sealing?

A dry gas seal is similar to a conventional balanced mechanical seal; it also consists of a stationary ring and a rotating ring. The stationary ring is spring-loaded and relies on O-rings for sealing. The end face material can be silicon carbide, silicon nitride, cemented carbide, or graphite. 　　The difference between a dry gas seal and a conventional liquid-balanced mechanical seal lies in the fact that the moving ring end face of a dry gas seal features gas grooves; the depth of these grooves is only a few micrometers. Clean gas must be present between the end faces to ensure the formation of a stable gas film that keeps the sealing end faces completely separated. The thickness of the gas film is generally a few micrometers. This stable gas film enables a certain sealing gap to be maintained between the sealed surfaces; if the gap is too large, the sealing effect deteriorates ； If the gap is too small, the sealing surfaces will come into contact; since the frictional heat generated by the dry gas seal cannot be dissipated, the lack of lubricated contact between the end surfaces will quickly cause deformation of those sealing surfaces, thereby leading to seal failure. 　　As the gas medium passes through the sealing gap, it is depressurized due to throttling and obstruction, thereby achieving sealing of the gas medium; a sealing gap of just a few micrometers keeps the gas leakage rate at a minimum. 　　The dynamic ring sealing surface is divided into two functional zones (outer zone and inner zone). In the outer area of the sealed gap where gas enters, there are aerodynamic pressure grooves that compress the incoming gas. To achieve the necessary pumping effect, the dynamic pressure groove must be provided on the high-pressure side. An increase in pressure within the sealing gap will ensure that a stable air film is formed that remains intact even under high axial loads. 　　The contact-free and wear-free operation of dry gas seals is ensured by a stable air film, which is generated by the throttling effect of the seal wall and the pumping effect of the pressure grooves. 　　The inner area of the sealing surface (sealing wall) is flat, and its throttling effect limits the amount of leakage. The spring force of a dry gas seal is very low; its main purpose is to ensure that the sealing surfaces remain closed when there is no pressure on the seal. 　　When selecting a dry gas seal, the decisive factor is the geometric shape of the dynamic pressure grooves on the rotating ring. For certain operating points of the compressor, such as during startup and shutdown, when a series of seals are in use at low speeds or under zero pressure conditions, the rotating dynamic pressure grooves must generate an appropriate pressure between the seal surfaces. This force is achieved through special measures: three-dimensional, curved grooves.

Liquid seals are commonly used, while gas seals are rarely used

We use it for the sealing of compressors. First, let’s understand what a dry gas seal is: A dry gas seal is a new type of contactless shaft seal that is used to seal gaseous or liquid media in rotating machinery. Compared to other sealing types, dry gas seals feature low leakage rates, minimal wear, long service life, low energy consumption, simple operation, reduced maintenance needs, and the ability to prevent the sealed fluid from being contaminated by oil. As a result, in the field of compressors, dry gas seals are gradually replacing floating ring seals, labyrinth seals, and oil-lubricated mechanical seals. The reliability and cost-effectiveness of dry gas seals have been proven by numerous engineering applications. 　　Currently, dry gas seals are mainly used in centrifugal compressors, as well as in axial flow compressors, gear-driven compressors, and turbine expanders. Dry gas seals have become an essential component for the proper operation of compressors. With the advancement of compressor technology, dry gas seals are gradually replacing floating ring seals, labyrinth seals, and oil-lubricated seals. 　　

There are certain limitations on the diameter of sealed shafts! What about low speed and large diameter (1000mm)?

Dry gas seal technology and applications for pumps I. Overview of dry gas seals A dry gas seal is a new type of non-contact seal that was developed in the late 1960s based on gas dynamic pressure bearings. This seal utilizes hydrodynamic principles to achieve non-contact operation of the sealing surface by creating dynamic pressure grooves on it. After several years of research, the British company John Crane was the first to apply dry gas seals to the gas transmission equipment on offshore platforms in the late 1970s, achieving success. Dry gas seals were originally developed to address the problems associated with shaft sealing in high-speed centrifugal compressors. Since they operate in a non-contact manner, the materials used for the sealing friction pairs are not significantly restricted by PV values, making them particularly suitable as shaft seals for high-speed, high-pressure equipment. As dry gas seal technology becomes more mature, its scope of application is also expanding. Currently, dry gas seals are gradually being used in centrifugal pumps and agitators. In short, dry gas seals can be used in any application that employs mechanical seals. Compared to mechanical seals, dry gas seals have the following advantages: 1. Long service life of the seal, with stable and reliable operation ； 2. The power consumption for sealing is low, at only about 5% of that of contact mechanical seals ； 3. Compared with other non-contact seals, dry gas seals have low gas leakage ； 4. It enables zero leakage of the medium, making it an environmentally friendly seal ； 5. The sealing auxiliary system is simple and reliable, requiring no maintenance during use ； II. Dry gas seal for centrifugal pumps – The medium transported by centrifugal pumps is liquid. Depending on the different operating conditions, the following sealing types can be used: 1. Double-end dry gas seal. The double-end dry gas seal can be applied to the shaft seals of virtually all centrifugal pumps. It has the following advantages: 1) It uses the principle of \"gas blocking\" instead of the traditional \"liquid blocking\" principle; in other words, pressurized sealing gas is used in place of pressurized sealing fluid, ensuring that there is \"zero leakage\" of the process medium” ； 2) The entire sealing system operates in a non-contact manner; its power consumption is only 5% of that of traditional double-end face seals, and its service life is more than 5 times longer than that of conventional seals ； 3) A auxiliary system with a simple structure ensures that the process medium remains unpolluted and does not leak into the atmosphere, thereby eliminating entirely the reliance on an oil system that is characteristic of traditional double-face mechanical seals. The sealing gas is industrial nitrogen or industrial instrument air, with a pressure 0.15–0.2 MPa higher than that of the medium. The disadvantages of double-end face dry gas seals for pumps are: 1) a gas source with a certain pressure is required, with the pressure of this source being at least 0.2 MPa higher than the pressure of the medium; 2) trace amounts of gas enter the process flow. 2. Series dry gas seal: The series dry gas seal used in pumps has the following characteristics: 1) The dry gas seal is used in series with a contact mechanical seal, where the mechanical seal serves as the primary seal and the dry gas seal functions as the secondary seal ； 2) Nitrogen is introduced between the dry gas seal and the main seal to ensure a certain back pressure for the main seal, thereby significantly extending its service life ； 3) The process medium that leaks from the main seal is discharged into the flare along with the sealing gas, thereby preventing the process medium from leaking into the atmosphere; this represents an environmentally friendly type of seal ； 4) After the primary seal fails, the dry gas seal acts as a primary seal in a short period of time to prevent massive leakage of the process medium into the atmosphere. 5) The service life of this type of seal depends on that of the mechanical seal, generally around 2–3 years. 6) This seal is primarily used in applications involving volatile media, such as liquid hydrocarbon media ； The requirement for the seal gas pressure is not high. The shortcomings of this seal are as follows: 1) It is not a true dry gas seal; its overall performance lies between that of a mechanical seal and a dry gas seal. 2) This seal is suitable for applications with volatile media, and its range of use is relatively narrow.

Simply put, it’s sealing gas with gas!

There are relevant posts on the forum: http://bbs.hcbbs.com/viewthread.php?tid=296512 HaiChuan Chemical Forum» Mechanical Technology Exchange Area » Mechanical Design Technology Exchange Area » Could someone introduce dry gas seals? Basic structural principles of dry gas seal technology: Generally speaking, a typical dry gas seal structure consists of components such as a stationary ring, a rotating ring assembly, a secondary sealing O-ring, a stationary seal, springs, and spring seats (cavities). The static ring is located within a stainless steel spring seat and is sealed by a secondary sealing O-ring. The spring brings the stationary ring into alignment with the movable ring assembly fixed to the rotor under sealed and unloaded conditions. There is an advanced and unique method for the radial gas sealing at the mating surfaces of the rotating ring component and the stationary ring. The fit surface features high flatness and smoothness; the fit surface of the moving ring assembly is equipped with a series of spiral grooves. As the rotor rotates, gas is pumped inward toward the roots of these spiral grooves. The area outside these grooves, without any grooves, is known as the sealing dam. The sealing dam exerts a resistive force on gas flow, increasing the gas film pressure. On the inner side of this sealing dam, there is also a series of reverse helical grooves; these grooves serve to pump fluid in the opposite direction and improve the pressure distribution on the mating surfaces, thereby enhancing the ability to increase the air gap between the stationary and moving ring components. Inside the reverse helical groove, there is also a sealing dam that exerts resistance to gas flow, thereby increasing the gas film pressure. The pressure between the mating surfaces causes the static ring surface to separate from the dynamic ring assembly, maintaining a very small gap, typically around 3 micrometers. A stable equilibrium gap is established when the closing pressure generated by gas pressure and spring force equals the opening pressure of the gas film. Under dynamic equilibrium conditions, the closing force Fc acting on the seal is the sum of the gas pressure and the spring force. The opening force Fo is generated by integrating the pressure distribution between the end faces over the area of those end faces. Under equilibrium conditions, Fc = Fo, and the operating gap is approximately 3 micrometers. If the sealing gap decreases due to some interference, the pressure between the end faces increases. At this point, the opening force Fo becomes greater than the closing force Fc, causing the end-face gap to increase automatically until equilibrium is reached. Similarly, if the disturbance causes the sealing gap to increase, the pressure between the end faces decreases; the closing force Fc becomes greater than the opening force Fo, the end-face gap automatically decreases, and the seal quickly reaches a new equilibrium state. This mechanism creates a gas film with high stability between the stationary and rotating ring components, allowing the end faces to remain separated, in contact with each other, and less prone to wear under normal operating conditions, thereby extending their service life. There is a ‘Dry Gas Sealing Lecture Notes’ document; the file extension is not supported, so it cannot be uploaded. Please understand! Search on the forum! You can take a look at this: http://bbs.hcbbs.com/thread-274323-1-1.html. Haicun Chemical Industry Forum » Transportation Equipment Technology Exchange Area » Transportation Equipment Technical Information Exchange Area » User Manual for Dry Gas Seals and Control Systems. http://bbs.hcbbs.com/thread-274323-1-1.html. User Manual for Dry Gas Seals and Control Systems. Table of Contents: I. Overview of Dry Gas Seals ……………………………………………………2 II. Description of the Structure of Dry Gas Seals ……………………………………5 III. Explanation of the Control System for Dry Gas Seals ………………………………7 IV. Installation and Dismantling of Dry Gas Seals …………………………………12 V. Operation and Maintenance of Dry Gas Seals …………………………………17 VI. Transport and Storage of Dry Gas Seals ………………………………………19 Figure 1: Assembly Diagram of Dry Gas Seal – CW (Drive End) Figure 2: Assembly Diagram of Dry Gas Seal – CCW (Non-Drive End) Figure 3: P&I Diagram of the Control System for Dry Gas Seals Figure 4: Overall Diagram of Installation and Dismantling Tools – CW (Drive End) Figure 5: Overall Diagram of Installation and Dismantling Tools – CCW (Non-Drive End) Figure 6: Schematic Diagram of Installation and Dismantling Steps. Attachment: User Manual for Dry Gas Seals and Control Systems.rar (52.6 KB). Date of upload: 2008-9-23 09:03; Number of downloads: 54; Reading rights: 30. This post was last edited by jindin312 on 2008-11-29 14:21

A dry gas seal is a new type of contactless shaft seal used to seal gas or liquid media in rotating machinery. Compared to other seals, dry gas seals feature low leakage rates, minimal wear, long service life, low energy consumption, simple and reliable operation, low maintenance requirements, and the fluid being sealed remains free from oil contamination. Therefore, in the field of compressor applications, dry gas seals are gradually replacing floating ring seals, labyrinth seals, and oil-lubricated mechanical seals. The reliability and cost-effectiveness of dry gas seals have been proven by numerous engineering applications. 　　 Currently, dry gas seals are mainly used in centrifugal compressors, as well as in axial flow compressors, gear-driven compressors, and turbine expanders. Dry gas seals have become an important element for the proper operation and reliable performance of compressors. With the advancement of compressor technology, dry gas seals are gradually replacing floating ring seals, labyrinth seals, and oil-lubricated seals. 　　 Analysis of the working principle of dry gas seals: Dry gas seals are similar to conventional balanced mechanical seals; they also consist of a stationary ring and a rotating ring. The stationary ring is spring-loaded and relies on O-rings for sealing. The end face material can be silicon carbide, silicon nitride, cemented carbide, or graphite. The difference between a dry gas seal and a conventional liquid-balanced mechanical seal lies in the fact that the moving ring end face of a dry gas seal features gas grooves; the depth of these grooves is only a few micrometers. Clean gas must be present between the end faces to ensure the formation of a stable gas film that keeps the sealing end faces completely separated. The thickness of the gas film is generally a few micrometers. This stable gas film enables a certain sealing gap to be maintained between the sealed surfaces; if the gap is too large, the sealing effect deteriorates ； If the gap is too small, the sealing surfaces will come into contact; since the frictional heat generated by the dry gas seal cannot be dissipated, the lack of lubricated contact between the end surfaces will quickly cause deformation of those sealing surfaces, thereby leading to seal failure. 　　 As the gas medium passes through the sealing gap, it is depressurized due to throttling and obstruction, thereby achieving sealing of the gas medium; a sealing gap of just a few micrometers keeps the gas leakage rate at a minimum. The dynamic ring sealing surface is divided into two functional zones (outer zone and inner zone). In the outer area of the sealed gap where gas enters, there are aerodynamic pressure grooves that compress the incoming gas. To achieve the necessary pumping effect, the dynamic pressure groove must be provided on the high-pressure side. An increase in pressure within the sealing gap will ensure that a stable air film is formed that remains intact even under high axial loads. 　　The contact-free and wear-free operation of dry gas seals is ensured by a stable air film, which is generated by the throttling effect of the seal wall and the pumping effect of the pressure grooves. 　　The inner area of the sealing surface (sealing wall) is flat, and its throttling effect limits the amount of leakage. The spring force of a dry gas seal is very low; its main purpose is to ensure that the sealing surfaces remain closed when there is no pressure on the seal. 　　 When selecting a dry gas seal, the decisive factor is the geometric shape of the dynamic pressure grooves on the rotating ring. For certain operating points of the compressor, such as during startup and shutdown, when a series of seals are in use at low speeds or under zero pressure conditions, the rotating dynamic pressure grooves must generate an appropriate pressure between the seal surfaces. This force is achieved through special measures: three-dimensional, curved grooves.

Generally speaking, a typical dry gas seal structure includes components such as a stationary ring, a rotating ring assembly, a secondary sealing O-ring, a stationary seal, springs, and spring seats (cavities). The static ring is located within a stainless steel spring seat and is sealed by a secondary sealing O-ring. The spring enables the stationary ring to fit with the moving ring assembly fixed to the rotor under a sealed and unloaded condition, and it features an advanced and unique method for radial gas sealing at the fitting surfaces of the moving ring assembly and the stationary ring. The fit surface features high flatness and smoothness; the fit surface of the moving ring assembly is equipped with a series of spiral grooves. As the rotor rotates, gas is pumped inward toward the roots of these spiral grooves. The area outside these grooves, without any grooves, is known as the sealing dam. The sealing dam exerts a resistive force on gas flow, increasing the gas film pressure. On the inner side of this sealing dam, there is also a series of reverse helical grooves; these grooves serve to pump fluid in the opposite direction and improve the pressure distribution on the mating surfaces, thereby enhancing the ability to increase the air gap between the stationary and moving ring components. Inside the reverse helical groove, there is also a sealing dam that exerts resistance to gas flow, thereby increasing the gas film pressure. The pressure between the mating surfaces causes the static ring surface to separate from the dynamic ring assembly, maintaining a very small gap, typically around 3 micrometers. A stable equilibrium gap is established when the closing pressure generated by gas pressure and spring force equals the opening pressure of the gas film.