Damage caused All can cause the pump seals to fail. Even though these mechanical seal faces also require some leakage across its faces, this leakage normally evaporates and is not noticeable. Wear down of the seal material Dry running Shocks and vibrations Wear down of the bearings Pressure drops or spikes What is a pump shaft seal? 4.Whining sound. Operators should be able to identify those reasons and do the correct maintenance when needed to ensure optimum productivity. Therefore, we need to detect the centrifugal pump seal condition. (3) Seal between moving and stationary rings. Seal leaks Short seal life 1. The other possibility is that one of the seal components such as the spring was damaged by contact, heat, corrosion, etc. 3. In a single type mechanical seal pump, this liquid is normally the fluid being handled by the pump. The abnormal sound of the water pump is the sound of friction generated during the rotation process, which is similar to the sound of rubbing. Dry Running Dry running is where a pump is operated without fluid. When a pump experiences rapid drops or spikes in fluid pumped, a pump can sometimes struggle to maintain the fluid within. Mechanical seal is a kind of shaft sealing equipment. In the meantime, here are a few of the most common causes of pump seal failure: Heat Exposure One of the most common contributors to pump seal failure is exposure to high temperature. Three 200-hp, high-pressure (HP) water pumps had pressure fluctuations in the . Mechanical-seal failure can also be caused by corrosion products and other particle debris in the liquid being pumped, so measures should be taken to remove these from the liquid, such as providing an adequate strainer in the pump-suction line. While Mechanical seal failures are the number one cause of Pump and Mixer down-time, this area represents a great opportunity to reduce whole life costs on site across all pump systems. Because the pressure in the sealing cavity is not accurate, the pressure in it exceeds the level that the mechanical seal can withstand, resulting in leakage. For a double mechanical seal running a . It is also one of the common causes of seal failure. Pump System Standards. Specifically, a major area of potential damage is the . The table below will be used to identify the seal under examination. If this happens for long enough, parts on the wet end (basket, trap, etc.) For those new to pump repair, mechanical seals can be intimidating. (4) static ring and static ring seat. thus causing premature seal failure and ultimately pump failure. A common cause of seal failures of centrifugal pumps is blocking in the pump while it is still running (or starting up the pump with the discharge block valve closed). The causes of leakage, generally speaking, corrosion, abnormal process fluctuations, material selection errors, etc. Sometimes operating conditions change to become. The seal absorbs the media, growing in volume to the point of malfunction. Damages to the pump's mechanical seals increase operating costs and reduce the efficiency of the pump. A mechanical seal is a wearing component, and it must be replaced . Stationary secon- dary rubber seal 3. Being that ammonia pumps are critical to maintaining temperatures at a cold storage facility, identifying the problem and appropriate solution was dire. Overheating of the seals when operating the pump without load or dry. Mechanical seals installed incorrectly: Many pump seals fail at initial start-up or prematurely because they were not installed correctly. Bad mounting. In . Seal drips steadily Seal squeals during operation. One of the most common is erosion, but it can also result from an improperly sized pump, which can lead to an imbalance of pressure. . Usually, this is not because of an incorrect seal design selection or a faulty seal, but simply because of the way the mechanical seal is operated. This often causes the O-ring to twist in upon itself. Pumps that move more viscous fluids such as paint can see buildup along the faces and edges of the seal. Taking a stopped pump from ambient temperatures up to immediately running an extreme high temperature or supercooled fluid can thermally shock the seal and cause cracking. Pump cavitation is caused by vaporization of the liquid in pump suction due to several reasons. Other times, failure is a result of poor selection or installation errors. Pump mechanical seals are available in a wide variety of models, there are five main leak points: (1) Seal between bushing and shaft. 3. Before using the pump, the shaft seal water must be turned on first. Seal fluid vaporizing at seal interface. Most pump shafts today are sealed by means of mechanical seals. The whine is the most noticeable aspect of a car engine water pump failure. mechanical seal, this thin liquid film, of necessity, leaks to the low pressure side of the seal, usually outside the pump. In centrifugal pumps, cavitation causes, damage to components (erosion of the material), vibrations, noise and a loss of efficiency. This type of issue is usually associated with O-rings, most often when a mechanism uses long strokes that are fairly fast. Introduction to failures 76 2. This document presents an investigation of the safety impact resulting from mechanical- and maintenance-induced reactor coolant pump (RCP) seal failures in nuclear power plants. This loss of prime may be due to air leaks on the incoming pipes, trap cover, low water . failure will occur well before the seal is actually "worn out". cause severe damage to the pump shaft. Pump mechanical seal design is challenging . Root causes of this are generally undersized suction lines, plugged suction strainer or valve issues. #2: Damage to Shaft Alignment Secondary seals nicked or scratched during installation. As you can see, there is a lot of overlap between the causes of leaks and overheating. Of course, volumes have been written as to why pumps fail. Failure of mechanical shaft seals 75 1. Leakage is a very common event during the operation of our device. In my August 2020 column, we began populating the fishbone using the cause and effect process. Pump cavitation can damage the pump impeller blades and frequent dry running of pumps can damage other pump parts. "The most common cause of pump downtime is a mechanical seal failure."1 Sometimes a mechanical seal can fail simply due to normal wear & tear. There are more complex designs with double, tandem or other arrangements which place a barrier fluid Then Man made pump seals. The pump seal faces may deteriorate rapidly, and. Pump seizures can occur for several reasons including off-design conditions, foreign objects entering the pump, or low flow operation. (5) The seal between the seal end cap and the pump body. may cause leakage. Mechanical Failure Modes Shaft Seizure or Break Bearing Failure Seal Failure Vibrations Mechanical seal condition is also related to the reduction of energy consumption and carbon emission. In some instances, seal manufacturers supply products with close clearances Gene Vogel EASA Pump & Vibration Specialist In the beginning, God made water to run freely over the earth. Stationary seat 4. Refer to the table below to help diagnose the problem. A mechanical seal is simply a method of containing fluid within a vessel (typically pumps, mixers, etc.) The top three reasons why a mechanical seal will leak are due to fluctuating pressure, damaged mechanical seal (or shaft/shaft sleeve) and excessive vibration. Then God made leaks. The shaft seal is exposed to widely varying operating conditions. This means internal parts which often rely on the pumped liquid for cooling and lubrication are subject to high amounts of friction and heat leading to prompt failure. The metal seal components may corrode. Operating a pump too close to shutoff head (left of the curve) or at runout (right on the curve) can result in bearing failure, mechanical seal failure or shaft breakage. How Excess Vibration Leads to Mechanical Seal Failure Mechanical equipment moves and vibrates. Symptoms & Causes of Mechanical Pump Failures. Pay special attention . At some point during the analysis, we may identify cause . Cavitation is, in many cases, an undesirable occurrence. Bad seal selection. . If a mechanical seal has failed and damaged the pump shaft, it's best to just replace it. Mechanical seal leakage caused by high pressure and pressure waves. Man continues to struggle with leaking pumps seals. Oftentimes, a mechanical seal is a "barometer" for the pump, helping maintenance and operators to understand the health of the pump on which it's installed. The swelling may occur across the entire O-ring or only in the places exposed to the chemical. Bearings Run hot and/or fail on regular basis. The high radial thrust resulting in excessive shaft deflections may lead to persistent packing or mechanical seal problems and possibly shaft failure. When a pump loses prime, or stops pulling the water to itself, this reduced or nonexistent flow of water causes the motor to run hot. Believe it or not, the pump is a truly ancient piece of technology. God laughed. In many pump systems, a mechanical seal is the first component to fail. Wear of internal wetted parts is accelerated. Axial thrust is imposed along the shaft axis. The mechanical seals used in centrifugal pumps can fail, requiring the removal of the pump for maintenance. Designers can alleviate this problem by switching to a polymeric material or to a different geometry, such as a square or X-ring. 1.1 Mechanical seal leakage caused by the wear of the end face of the dynamic and static ring 1.2 Mechanical seal leakage due to unstable process conditions and wrong installation 1.3 Failure of sealing ring of mechanical seal is also the main cause of seal leakage 1.4 Mechanical seal leakage due to improper assembly may warp and the motor is susceptible to burnout. One possibility is that the seal face has opened because it became jammed on the rotating component. We focused said process on the mechanical seal failures as the other failures (shim packs, bearings) require a separate investigation/root cause failure analysis (RCFA). Mishandling of seals before installation and introduction of dirt, oil, or any other abrasive material can also cause damage that gets worse as the pump runs. 1. . Even with adequate leakage for lubrication, pump shaft wear was a . API STD 682 [ 1] gives additional information on pump mechanical seal systems. Also, it is no stretch to assert that, when pump fires result from such failures, a mechanical seal is usually involved (Fig. The pump may have only one seal or the pump might have, for example, tandem seals on each end of the pump. Vibration hurts your equipment and can result in damaged seals and shortened seal life. PUSHER VS. NON-PUSHER HAMMERING COUPLINGS ONTO THE SHAFT When it comes to pumps, hammers are not friends! Here are some common issues we've seen occur in the installation process: Not tightening the set screws before removing the setting clips Not tightening gland bolts evenly Damaging O-rings or seal faces from lack of care Lack of knowledge or understanding resulting in improper installation 2. Pump Failure Point #1: Seals. Lubrication failures 77 3. . However, because of the delicate components used for this new sealing method, mechanical seal failures are the greatest cause of pump down time. In the production equipment, the commonly used conveying machinery-pumps, leakage incidents are also everywhere. The 0-rings may swell locking up the pump seal, 2. As the engine runs faster, the water pump noise becomes louder. Metal components within the pump often exacerbate seizures, resulting in significant pump damage. Mechanical seal failures are often the initial reason such pumps are brought down for maintenance or repair. Failure of the mechanical shaft seal is the most common cause of pump downtime. Other causes include improper bearing selection, overload, fatigue and many more. Face wear is one of the main causes of mechanical seal failure. The Main Causes of Vibration in Pumps. When sealing a centrifugal pump, the challenge is to allow a rotating shaft to enter the 'wet' area of the pump . High axial thrust may impose an excessive load on the bearing. Preventing Excess Heat Generation Torque transmission A pump should operate within 30 percent of its BEP to avoid these failures, maximizing the pump's life span and power consumption. Often, however, the seal is not to blame. Blistered carbon graphite seal face. The typical design life for a mechanical seal is 3 yr. As such, premature failures need to be analyzed to identify the causes of the failure. Speed: By being too quick for the seal, bringing on unnecessary wear on the seal faces, and additionally creating exorbitant warmth which typically assaults (or melts) the optional seals . This begs for a better understanding of this seal type and its application. Excessive shaft run-out can cause: Excessive dynamic mechanical seal leakage / vibration of pump shaft / bearing failure. Seal failure rates are generally in excess of 85%. 5. POSSIBLE CAUSES 1. Symptoms & Causes of Mechanical Pump Failures. The following is a case history of a mechanical seal failure for the non-drive-end (NDE) seal of a high-pressure water pump.
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