The guide explains how tandem dry gas seals work and outlines key steps for compressor preparation, installation, operation, leakage monitoring and maintenance.
GUANGZHOU, China, Nov. 11, 2026 /PRNewswire/ — Lepu Seal, a mechanical seal manufacturer and dry gas seal supplier, has published a practical guide for technicians who install and maintain tandem dry gas seals on compressors. It follows the work from the initial compressor checks to fitting and removing the seal. It also explains what operators need to watch while the machine is running, including seal gas supply, leakage and changes in operating conditions. The guide covers cleaning, inspection, storage and transportation as well.
Cross-sectional structure of a dry gas seal showing its main components and their arrangement.
How a Tandem Dry Gas Seal Works
A typical dry gas seal has a rotating ring fixed to the compressor shaft and a stationary ring held inside a stainless steel spring seat. Secondary O-rings seal the stationary ring within the seat. Static O-rings and springs are also part of the assembly. When the shaft is at rest, the springs press the two sealing faces together.
As the shaft turns, rotation drives gas inward through the arc grooves on the rotating face, toward the roots of the grooves. The smooth area beyond the grooves forms the sealing dam. It restricts gas flow and allows pressure to build between the rotating and stationary faces. As pressure rises, the stationary ring lifts slightly, leaving a thin film of gas between the faces.
Two forces act on the seal during operation. Gas pressure and spring force push the faces together, while pressure within the gas film pushes them apart. At normal operating conditions, these forces balance and leave a gap of approximately 3 microns between the sealing faces.
The gap changes as the pressure between the faces changes. When the gap becomes smaller, gas film pressure rises and pushes the faces apart. When the gap widens, film pressure falls and the closing force moves the faces closer together. This adjustment allows the seal to maintain its operating gap as the compressor runs.
Preparing the Compressor Before Installation
Before installing the seal, technicians should clean the inlet piping, the inlet and outlet ports in the compressor casing, and the entire seal installation area. The mating surfaces need to be checked for deposits, scratches and other damage. Particular attention should be given to the surfaces that contact the static O-rings. Any defects in these areas should be corrected before installation.
The shaft and its mounting surfaces also need inspection. The shaft shoulder should be perpendicular to the shaft axis within 0.01 mm. The radius at the root of the shaft shoulder should not exceed 1 mm. Technicians should also check the edges along the seal’s installation path and make sure they have suitable chamfers.
The compressor rotor must be moved into its operating position before the seal is fitted. Technicians should check the rotor’s position in relation to the casing and adjust the shim thickness according to the assembly drawing when necessary.
The specified grease and anti-seize compound should be used sparingly. A thin layer of grease should be applied to the relevant installation surfaces. Excess grease or anti-seize compound can affect seal performance. O-rings also need a thin coating of the specified grease before fitting.
Installing and Removing the Cartridge Seal
The tandem dry gas seal uses a cartridge assembly. Its rotating and stationary components are assembled together before installation. A setting plate and connecting screws hold the components in position while the seal is handled and fitted.
Before installation, technicians must check that the rotation direction marked on the seal matches the actual direction of the compressor shaft. The specified shim is then fitted onto the shaft, with its chamfer facing the correct direction.
The cartridge assembly is moved along the shaft to its working position using the dedicated installation tool. Technicians then secure the seal housing to the equipment and remove the setting plate and connecting screws. A small amount of anti-seize compound is applied to the threads and inner bore of the shaft locknut before the locknut secures the main seal to the shaft. The same installation procedure applies to both ends of the compressor.
For removal, technicians first take off the shaft locknut using the removal wrench. They then reinstall the setting plate and connecting screws before removing the bolts that connect the seal to the equipment. The dedicated removal tool is used to withdraw the cartridge assembly.
The sealing faces and O-rings need careful handling throughout installation and removal. The work should be carried out by experienced technicians who understand dry gas seal operation and know how to use the installation tools. Less experienced personnel should work under the supervision of qualified technicians.
What to Monitor During Compressor Operation
The gas entering the seal should be clean and dry. The operating guide recommends a 2 μm filter in the seal gas supply line and a sufficient supply of filtered gas throughout compressor operation.
A tandem dry gas seal can tolerate some liquid contamination, but continuous contamination, particularly from bearing oil, should be avoided. The seal chamber should also remain free of liquids and solid particles.
Operators should monitor the leakage rate and record it daily. Brief increases can occur during process fluctuations, shaft movement or changes in pressure, temperature and rotational speed. Alarm settings should allow for occasional spikes caused by these operating changes. A sustained change in the leakage trend calls for further investigation.
Reverse pressure also needs attention. Under static conditions, it can increase leakage. Under dynamic conditions, it may damage the seal.
The operating guide advises against continuous operation below 1,000 rpm. Above this speed, the seal has a greater operating margin and can maintain a stable running gap. It also states that brief shaft turning at 12 rpm while the system remains pressurized will not damage the seal.
The recommended depressurization rate is generally 0.8 MPa per minute. Faster depressurization depends on the specific application. Compressor vibration should also be monitored. The seal can withstand relatively high vibration levels, but excessive vibration may still cause damage.
Cleaning, Inspection and Storage
The seal is designed to cover a wide range of operating parameters without routine maintenance to the seal assembly. Operators should still monitor leakage, keep the seal chamber clean and follow the required inspection schedule.
If oil or other contaminants enter the seal, the unit should be returned to the manufacturer for cleaning. Customers should contact Lepu Seal’s technical team for guidance on the cleaning and inspection process.
The seal chamber should be reconditioned periodically. The required interval depends on operating loads and environmental conditions. The guide specifies that O-rings should be replaced three years after shipment. O-ring replacement and routine inspection should be arranged through Lepu Seal’s technical team.
Proper storage helps protect the sealing faces and other components. The seal should remain fully assembled, with the setting plate correctly installed as shown in the assembly drawing. For storage, it should be wrapped in plastic film, such as polyethylene, with a small pack of desiccant added where possible. The wrapped seal should then be placed in a wooden crate with foam padding and kept in a warm, dry environment.
Grease, oil paper and cotton cloth should not be used as packing materials. When a seal remains inside a compressor during an extended storage period, the sealing faces should remain free of oil and should be kept from sticking together. During transportation, the setting plate must remain secured to prevent movement between the rotating and stationary components. Loose or unsecured parts should not be placed in the package.
Dry Gas Seal Solutions and Technical Support from Lepu Seal
For a compressor project, seal selection starts with the equipment details. Buyers can share the compressor model, shaft dimensions, process medium and operating conditions with Lepu Seal’s technical team when discussing a suitable tandem dry gas seal configuration.
About Lepu Seal
Guangzhou Lepu Machinery Co., Ltd., operating under the Lepu Seal name, supplies mechanical seals and dry gas seals for industrial applications. Its product range includes cartridge seals, bellows seals, O-ring mechanical seals, dry gas seals and related sealing products. As a mechanical seal manufacturer and dry gas seal supplier, Lepu Seal also offers OEM and ODM services for customers developing or sourcing sealing products for specific equipment. For more information, visit www.lepuseal.com.
Media Contact
Company: Guangzhou Lepu Machinery Co., Ltd.
Address: No. 5, Yunkai Road, Huangpu District, Guangzhou, China
Tel: +86-020-36158139; +86-020-36158280
Email: [email protected]
Fax: +86-020-36158281
Contact Person: Mr. Mark Ao
WhatsApp: +86-18903009893
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