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evg seals are materials or components that prevent leakage of fluids or solid particles from adjacent mating surfaces and prevent external contaminants such as dust and moisture from entering machinery. The recommended storage temperature for seals is below 30 °C to avoid high-temperature aging. Seals are classified into static seals and dynamic seals. Their main function is to prevent leakage of fluids or solid particles from adjacent mating surfaces and to prevent external contaminants such as dust and moisture from entering machinery. Static sealing refers to the tight closure of sealed chambers or containers used for sealing letters and testamentary seals.

evg seal classification

1) Packing seal: The packing seal has a simple structure, low cost, and is easy to maintain. However, it has high leakage and significant power loss. Therefore, packing seals are used for general media such as water; they are generally not suitable for petroleum and chemical media, especially for valuable, flammable, explosive, or toxic media. 2) Mechanical seal: Mechanical seals (also known as face seals) provide good sealing performance with minimal leakage and long service life, but they are expensive and require higher standards for machining, installation, maintenance, and repair compared to general seals. Mechanical seals are suitable for transporting petroleum and chemical media and can be used with media of various viscosities, strong corrosiveness, and containing particles. The American Petroleum Institute standard API610 (8rd edition) stipulates that cartridge mechanical seals shall be installed unless otherwise specified by the user. 3) Dynamic seal: Dynamic seals are divided into back-vane seals and auxiliary impeller seals. During pump operation, the centrifugal force of the back vanes (or auxiliary impeller) reduces the pressure at the shaft seal to atmospheric or negative pressure, preventing leakage during use. When the pump stops, the centrifugal force disappears, and the sealing effect of the back vanes (or auxiliary impeller) fails; at this point, the stationary sealing device provides the seal. Packing seals are commonly used in the stationary sealing devices associated with back-vane (or auxiliary impeller) seals. Packing seals come in two types: standard and mechanically adjustable. Standard packing seals are similar to those in general packing seal pumps and require maintaining a slight positive pressure at the shaft seal to avoid dry friction of the packing. Mechanically adjustable packing seals use counterweights to loosen the packing during pump operation and tighten it when stopped. Dynamic seals offer reliable performance, low cost, and easy maintenance, making them suitable for media containing many solid particles, such as slurry pumps and feed pumps in the phosphate industry. The disadvantages are greater power loss compared to mechanical seals and shorter service life of the stationary sealing device. The seal between the rotating pump shaft and the stationary pump casing is called the shaft seal. Its function is to prevent high-pressure liquid from leaking out along the shaft or air from entering along the shaft. For centrifugal pumps, the shaft seal is a type of dynamic seal. Depending on whether the sealing surfaces are in contact, dynamic seals are classified as contact or non-contact. In contact dynamic seals, the sealing device contacts the shaft, resulting in relative friction. Contact dynamic seals include packing seals and mechanical seals.

evg seal operation

1) If slight leakage occurs after the pump starts, observe it for a period. If the leakage does not decrease after 4 hours of continuous operation, stop the pump for inspection. 2) The pump operating pressure should be stable, with pressure fluctuations not exceeding 1 kg/cm². 3) During pump operation, avoid cavitation to prevent dry friction and damage to the sealing surfaces. 3) Inspect the sealing condition regularly. During operation, if leakage exceeds the standard (no more than 5 drops/min for heavy oil and no more than 10 drops/min for light oil), and there is no improvement within 2-3 days, stop the pump to inspect the sealing device.

evg seal maintenance

1) Control of shaft seal pressure: High shaft seal pressure can cause steam leakage at the shaft seal, leading to water ingress into the oil and deterioration of turbine oil quality. Excessively high shaft seal pressure may trigger the safety valve of the equalizing tank, wasting working fluid and damaging equipment. Low shaft seal pressure may cause a drop in unit vacuum, allowing cold air to enter the shaft seal or even the cylinder, causing cooling of the shaft seal section or inside the cylinder, which seriously threatens equipment safety. 2) Impact of abnormal shaft seal temperature on the unit: Excessively high shaft seal temperature, especially before unit startup, causes intense heating at the shaft end gland and rotor gland sections, leading to local stress concentration and deformation. This may change the clearance between the rotor and cylinder, increase steam leakage at the shaft seal, increase differential expansion, and potentially cause rubbing between rotating and stationary parts. Low shaft seal temperature cools the shaft end gland and rotor gland sections, also causing local stress concentration, changing the clearance between the cylinder and rotor, increasing steam leakage at the shaft end, and reducing differential expansion. Low shaft seal temperature may also cause water carryover in the shaft seal supply steam, leading to water hammer in the supply pipes. In severe cases, this can cause water ingress into the turbine.

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