A Comprehensive Guide to Valve Gaskets Installation

In the world of machinery and equipment, gaskets may be small, but they play a crucial role. They act as the "guardians" of mechanical sealing systems, preventing the leakage of liquids or gases and ensuring the normal operation of equipment. However, even the best gaskets can lose their effectiveness and even pose safety hazards if not installed properly. So, how can we install gaskets correctly? Don't worry, I'll provide a detailed answer for you.

Preparation is essential before installing a gasket. First, carefully inspect whether the flange or threaded connection structure is intact, whether the static sealing surface is flat, and whether the gasket is damaged. Any issue with these components can affect the sealing performance of the gasket. After the inspection, ensure that the sealing surface, gasket, threads, and the rotating parts of bolts and nuts are clean and free of impurities. You can apply a lubricant made of graphite powder or a mixture of engine oil (or water) to reduce friction and prevent rust, thereby extending the life of the components. Meanwhile, keep the gasket and graphite clean to avoid mixing in impurities that could affect the sealing performance.

After completing the pre-installation preparations, we move on to the key part of gasket installation. The correct installation method is the core to ensuring the sealing function of the gasket. Below, I will detail the installation points and precautions for different types of gaskets.

The gasket should be centered and correctly installed on the sealing surface, without any tilt or extension into the valve chamber or placement on the shoulder. When installing a gasket, only one piece is allowed; it is absolutely forbidden to install two or more gaskets between the sealing surfaces to eliminate insufficient gaps. This not only fails to achieve the sealing effect but also damages the gasket and causes leakage.

Oval Gasket: When installing an oval gasket, pay special attention to the contact between the inner and outer rings of the gasket. The end faces of the gasket must not contact the bottom of the groove. This ensures the sealing effect and prevents leakage due to improper installation.

O-Ring: In addition to the ring and groove meeting the design requirements, the compression amount of the O-ring should be appropriate. Under the premise of ensuring sealing, the smaller the compression deformation rate, the better, which can extend the life of the O-ring. During installation, ensure that the O-ring is correctly positioned in the groove and avoid twisting or deformation.

Flat Gasket: When installing a flat gasket, ensure that the gasket is tightly attached to the flange sealing surface. Before installation, the sealing surface can be ground to make it flatter. Then, apply a layer of adhesive evenly, expel air, and ensure the adhesive layer is of uniform thickness, generally 0.1-0.2mm.

Valve Status: Before installing the gasket, the valve should be in the open position to avoid affecting the installation and damaging the valve components.

Installation Position: When covering the gasket, align it correctly. Do not use pushing or pulling methods to contact the gasket to prevent displacement and scratching.

Bolt Connection: For gaskets installed with bolt or threaded connections, the gasket should be in a horizontal position. For threaded connections, do not use a pipe wrench if there is a wrench position to avoid damaging the gasket or threads.

Pre-tension: Before tightening the gasket, understand the pressure, temperature, nature of the medium, and characteristics of the gasket material to determine the pre-tension. The pre-tension should be minimized while ensuring no leakage during testing. After the gasket is tightened, there should be a pre-tension gap in the connection to allow for further tightening in case of gasket leakage.

After mastering the basic installation methods of gaskets, we also need to understand some installation techniques for special working conditions.

When working at high temperatures, bolts may experience high-temperature creep, leading to stress relaxation and increased deformation, which can cause leakage at the gasket. Therefore, hot-tightening is required. Hot-tightening involves re-tightening the bolts after the equipment has reached the working temperature to compensate for the reduction in pre-tension due to high-temperature creep.

Conversely, in low-temperature conditions, bolts will contract, and cold-loosening is necessary. Cold-loosening means slightly loosening the bolts after the equipment has cooled down to prevent excessive pre-tension due to bolt contraction, which could damage the gasket or sealing surface.

When using liquid gaskets on the sealing surface, the surface should be cleaned or treated. Flat sealing surfaces should be ground to fit together, and adhesive should be applied evenly to expel air and ensure a good seal.

When using PTFE film tape for threaded seals, start by pulling the film thin and sticking it to the thread surface. Remove any excess tape at the starting point to form a wedge shape on the thread. This ensures the reliability of the threaded seal and prevents leakage.

Gasket removal is equally important. The correct removal method can avoid damaging the gasket and sealing surface, facilitating subsequent maintenance and replacement.

The sequence for removing a gasket is: relieve the pre-tension on the gasket → open the static sealing surface → remove the gasket → clean up any gasket residue. This sequence must not be reversed, otherwise, it may damage the components or cause leakage.

Thread Treatment: Soak the threads with kerosene or rust remover to remove rust and increase lubrication, making it easier to disassemble the parts.

Relieving Pre-tension: Loosen the bolts symmetrically, evenly, and in turns by 1/4 to 1 turn, then remove the bolts. This prevents damage to the components due to excessive local stress.

Wedging the Flange: Insert a wedge tool between the flanges and gently pry the flange to be removed. Carefully insert the tool into the gap between the gasket and the sealing surface, and pry symmetrically to loosen the gasket before removal.

Special Treatment: For rusted or adhered gaskets, first remove the bolts, then close the valve, and use the valve stem to lift the valve cover. Gently tap the valve body with a copper rod or hand hammer to loosen the parts and gasket before disassembly. Alternatively, soak the gasket with a solvent or kerosene to soften or release it from the sealing surface for removal. For difficult-to-remove residues, use a scraper with a beveled edge to remove the gasket and its residues. For rubber asbestos gaskets and tightly adhered rubber layers, use a scraper with the beveled edge against the sealing surface. Apply force cautiously and evenly to avoid damaging the sealing surface. For sealing surfaces with water lines, use a steel wire to make a beveled triangular blade to remove residues from the grooves.

After understanding the installation methods and techniques for special working conditions, let's summarize the five key points for gasket installation.

The form, material, and size of flanges, bolts, and gaskets should be appropriately selected based on operating conditions and the structure of the flange face. Different working conditions have different requirements for gaskets, and choosing the right material and size is crucial for ensuring sealing performance.

Before installation, carefully inspect the quality of flanges, bolts, nuts, and gaskets. There should be no burrs, unevenness, cracks, or other defects. These defects can lead to an uneven sealing surface, affecting the sealing effect.

Carefully inspect the installation of flanges and pipes to ensure there are no misaligned, mismatched, or misaligned holes. The flange sealing surface must be cleaned, and bolts and gaskets must not be contaminated with impurities or oil. These details can affect the sealing performance of the gasket.

The gasket should be concentric with the pipe or fitting. When tightening bolts and nuts, apply force evenly and tighten symmetrically in multiple steps. This ensures even force distribution on the gasket, preventing damage or leakage due to excessive local force.

After the flange gasket is installed, it should be tested at working pressure to ensure no leakage. Pressure testing is the final step to verify the sealing performance, and only passing this test can ensure the reliability of the gasket installation.

After installation, don't forget to clean and maintain the tools. Keeping tools clean and in good condition not only extends their lifespan but also ensures their reliability for future use. At the same time, handle the components carefully to avoid damaging parts such as the flange. After completion, clean up the work area to ensure safety and tidiness.

Although gasket installation may seem simple, it involves many details and techniques. Only by strictly following the correct steps and methods can we ensure the reliability of the sealing performance and the normal operation of the equipment. I hope this article helps you better understand and master the skills of gasket installation, making your practical operations more efficient. Remember, details determine success or failure, and the correct installation method is the key to worry-free sealing.