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This post was last edited by Zunming Machinery on 2023-8-9 at 10:05. 01: Do you hear a cracking sound during dry running? That is the sound produced when the mechanical seal is operating dry. Mechanical seals are designed to use a small amount of process fluid between the sealing surfaces, which keeps these surfaces lubricated and cooled. However, when the liquid vaporizes between the sealing surfaces, an audible popping sound is produced. The following are the common causes of lubricant/coolant vaporization: 1) Improper axial adjustment 2) Air entrainment 3) Steam retention in the stuffing box 4) Solid retention in the stuffing box 5) Pump operation in a dry condition 6) Insufficient cooling 7) Absence of a flushing system or incorrect installation of such a system 8) Excessively high vapor pressure of the fluid. Figure 1: Example of severe thermal damage (coking) caused by dry operation. Figure 2: Damage to the sealing surfaces due to dry operation and mechanical deformation. How to prevent or repair it: To avoid dry operation, heat should be kept away from the mechanical sealing surfaces by increasing the flushing flow rate or by reevaluating the design of the stuffing box, as well as the sealing and flushing systems. Release the trapped steam by evacuating the gas from the stuffing box gland or using a tapered-hole stuffing box gland. 02 High temperature: If radial cracks (thermal cracks) or deposits (coking) are seen on the sealing surface, it may be due to excessive temperature. In this case, the high temperature faced by the seal is caused by the heat generated during the operation of the pump or the seal. Thermal cracking can be identified by radial cracks that appear at the center of the sealing surface (see Figure 3). These cracks act as cutting edges, causing premature wear when the sealing surfaces rub against each other. Figure 3: Radial thermal crack scaling originating from the center of the sealing surface; this scaling leaves deposits or abrasive debris on the atmospheric side of the mechanical seal. This accumulation occurs when the seal operates at excessively high temperatures, but it can also be caused by factors such as dirty flushing fluid or contamination from the external environment (see Figure 4). Figure 4: An example of coking in a pump – when it operates away from the BEP on its performance curve, excessive heat is generated ； Sealing generates excessive heat due to high-speed operation or excessive pressure applied to the sealing surfaces. Some sealing materials are not designed for high-temperature applications. When pumping high-temperature liquids, using incorrect structural materials can lead to premature failure of the mechanical seal. How to prevent or repair it is crucial for maintaining sealed cooling and ensuring its long-term reliable operation. If signs of hot cracking or coking can be seen, it is time to carefully examine the sealing flushing scheme (or it may be necessary to enhance it). Consider increasing the flushing flow rate or changing the flushing scheme. Has the correct seal been selected for the application? The correct structural materials and sealing design ensure that the seal can withstand high temperatures. 03 There are several different types of shocks that can cause mechanical seals to fail, including mechanical shock and thermal shock. Figure 5: Example of impact damage. Mechanical shock is caused by deteriorating equipment conditions, such as bearing damage, cavitation, excessive torque, uneven loading, and shaft misalignment. However, more commonly, mechanical shock is caused by improper sealing and assembly. Thermal shock occurs when a seal is exposed to large temperature fluctuations over a short period of time. Different areas of the sealing surface experience varying degrees of expansion and contraction, thereby causing excessive stress or strain on the sealing surface. How to prevent or fix it? How to address this special situation? First, it is necessary to fully understand the reasons behind it. When dealing with shocks, keep the following points in mind: 1) When installing mechanical seals, avoid uneven or excessive tightening of the fasteners. 2) Make sure to use a flushing scheme that is suitable for the seal being installed. 3) Check to ensure that the design of the flushing fluid and quenching system minimizes the risk of any sudden interruptions. 4) Include vibration checks as part of regular routine inspections. 5) If the operating parameters specify a large temperature difference, as a general rule, limit the variation to 1°F per minute. 04 Poor lubrication: If a mechanical seal emits a screeching sound during operation, it may be due to a lack of lubrication between the sealing surfaces. Lubrication plays a key role in the operation of mechanical seals. In addition to lubrication, its functions include cooling, sealing, cleaning the sealing surfaces, and providing protection. Poor lubrication on hard surfaces (such as silicon carbide or ceramics) can lead to thermal cracks. Thermal cracking shows radial cracks on the sealing surface. The height and distance between cracks can range from very small to very large (see Figure 6). When two rotating surfaces come into contact under heavy loads, local high temperatures may occur due to excessive frictional heating near the surface. Fever, poor lubrication between the sealing surfaces, and mechanical loads combined to cause cracking in the material near the contact area. Figure 6: Example of damage caused by poor lubrication. How to prevent or repair it – ensure that operating conditions such as seal chamber pressure are within the limits specified by the seal design ； Confirm that the sealing chamber has already or can fully exhaust air ； Provide sufficient and continuous (lubricating) flushing for sealing. 05 Speed/Torque: This is true for almost any rotating device; speed is often fatal. High starting or operating torque, as well as frequent start-up/shutdown of the equipment, can damage mechanical seals. Figure 7: How to prevent or repair high-torque damage by checking the condition of the equipment and restoring it to an appropriate level. Select an appropriate drive mechanism based on torque or other operating conditions of the equipment. Use balanced seals to reduce seal surface torque and pressure torque. 06 Some of the most severe damages to mechanical seals may stem from chemical erosion. Incompatible materials can have a tremendous impact. When seals are subjected to chemical erosion, any of the following may occur: 1) severe leakage, 2) signs of excessive wear, 3) fragile or damaged components, 4) pitting on the sealing surfaces, 5) corroded metal parts, 6) swollen O-rings. Figure 8: Examples of damage caused by chemical erosion. Chemical erosion results from improper selection of seals and their structural materials. The selection of mechanical seals must be carried out by personnel with extensive experience in different materials used for such seals; it is also crucial to have an understanding of how they react to certain chemicals. To prevent or repair this issue, a thorough chemical analysis should be conducted in order to select the appropriate material for the process fluid. When selecting a sealing material, please thoroughly understand all possible operating conditions to which the seal will be exposed, including the properties of the cleaning chemicals and their operating temperatures. Choose a rinsing solution that uses clean, compatible liquids. In some cases, a dual mechanical seal may be required to neutralize or control corrosive environments.