This document is intended to clarify what to expect on mechanical seals found in colfax products. Even though these mechanical seal faces also require some leakage across its faces, this leakage normally evaporates and is not noticeable. For this particular analysis of mechanical seal failure, data from mechanical seal failure were collected from cmms system to determine the time to failure for every mechanical seal and then to be computed in a specific software for weibull analysis reliasoft. Here are some reasons why a mechanical seal face would open. Mechanical seal failures are often the initial reason such pumps are brought down for maintenance or repair. Manager reliability improvement hpcl mumbai refinery mumbai, india many different factors contribute towards the failure of a pump. Pdf unique failure mode for double mechanical seals api seal. If you are unable to identify the seal, it will be necessary for you to. Introduction to failures failure of the mechanical shaft seal is the most common cause of pump downtime.
Mechanical seal failure has an effect on many different parts of a pump, including the pump shaft. Checklist of problems vvith centrifugal pumps and their causes centrifugal pumps are one of the worlds most commonly used devices. The mechanical seal faces may deteriorate rapidly, and 3. Mechanical seals also have a number of unique failure modes that can be. Problems at the faces carbons, ceramic, silicon and tungsten carbide faces. How to respond to mechanical seal leakage in a centrifugal pump. Failure of mechanical sealfailure of mechanical seal cause of failure. Such failure will normally occur at approximately 6month intervals regardless of the type of seal or bearing installed. Unique seal failure modes mechanical seals also have a number of unique failure modes that can be difficult to determine due to the relative. Centrifugal pumps are the most common type of power machinery in fluid handling.
Root cause on seal failure in refinery maintenance world. By design mechanical seals are friction contact devices and can be subjected to a very wide range and often hostile operating environments. Root cause on seal failure in refinery by sourav kumar chatterjee sr. Operators and engineers in plants of all sizes and industries will vouch for it. A design engineer may be able to reduce the damage inflicted on hydraulic seals if they keep in. List of centifugal pump set failure modes, pump failure. Sometimes operating conditions change to become quite different from the specific conditions for which the seal was intended. Accessible via desktop, tablet and mobile devices, this app is an invaluable resource for. The seal ring which rotates with the shaft is called the rotary ring. In the first three articles of my recent series case study. Sealing systems for pumpssealing systems for pumps part i.
Click here for full pdf version of this article includes all graphs, charts, tables and. Extend mechanical seal life fluid sealing association. Indisputably, mechanical seal failure is the most common cause of pump downtime. Causes for failures of centrifugal pump mechanical seal. The breakdown of a pump seal can lead to more damage to the pump itself, so its important to take notice of the warning signs and not let it grow into a larger problem.
Mechanical face seal replacement how to use this catalogue locate the manufacturer of the equipment. Failure analysis and troubleshooting mechanical seals and. In this blog, we will talk about most common causes of seal failure and how to prevent such frequent failures. In fact, seal related repairs represent approximately 60 to 70% of all centrifugal pump maintenance work. Improperly starting the pump can cause the motor to trip and the shaft to twist causing orbital movement, resulting in internal parts contact, seal failure, and shortened bearing life.
However, because of the delicate components used for this new sealing method, mechanical seal failures are the greatest cause of pump down time. The orings may swell locking up the mechanical seal, 2. Mechanical fuel pumps basic information and troubleshooting the standard mechanical fuel pumps found on classic cars are very reliable. Study of centrifugal pump using failure mode effect and. Improving the reliability of mechanical seals peerless pump. Mechanical seals are used in industrial pumps, compressors, and other applications to provide a leakproof seal between component parts. A pump should operate within 30 percent of its bep to avoid these failures, maximizing the pump s life span and power consumption. Cracked seal face thermal shock mechanical shock or impact.
Possible causes of mechanical seal failures by william forsthoffer. Learn how to visually identify and prevent mechanical seal failures with this easytouse reference tool. Centrifugal pumps are common process plant equipment and here is a useful list of pump failure modes to understand what can cause centrifugal pumps to fail. Cavitation as liquid pressure falls below its vapor pressure, bubbles form and implode on impellers and interior surfaces, damaging pump internals, disrupting flow and leading to seal failure. Some factors that did not seem to have contributed to earlier failures were not examined or. Mechanical seals are one of the weakest links in pumps and turbomachines. Causes for failures of centrifugal pump mechanical seal and its improvement measures. In addition, these same techniques will be applied to monitoring opportunities for mechanical seal piping plans in operations. All of these techniques will focus on identifying true root causes and creating effective corrective actions to prevent the reoccurrences of failures.
The ignorance of such symptoms almost always leads to failure. The function of every mechanical seal is to prevent the escape of a fluid past the clearance between a rotating shaft and the passageway through the wall of a housing or pressurized vessel. Also, in case of any mechanical failure or physical damage of pump internals, the operating engineer should be able to relate the failure to the process. With that said, nothing automotive lasts forever and at some point mechanical fuel pumps will fail. Maintenance and troubleshooting of progressing cavity pumps.
Diagnosing common causes of sealing failures peerless. This paper represents the generic process of fmeca for centrifugal pump failures and a case study on centrifugal pump failure cost estimation actual and after implementation of optimum strategies of maintenance. Loss of pump head external leakage seal failur e worn mechanica seal l scored shaft sleev e stuffing box improperl packey d depend osn type of fl uid and criticality as to time of failure mechanical noise debri isn the impeller. The stationary part of the seal is fitted to the pump housing with a static seal this may be sealed with an oring or gasket clamped between the stationary portion and the pump.
To avoid this, its essential to apply the right seal for the desired, and appropriate, function. 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. Failure of any of these components will cause failure of the entire system. Early detection of abnormal conditions such as cavitation, pressure imbalance or excess vibration can help avoid leaks and their consequences. The shaft seal is exposed to widely varying operating conditions. To find out how seal failure affects the pump shaft, i talked to one of our most experienced service technicians. Unique sealfailure modes mechanical seals also have a number of unique failure modes that can be difficult to determine due to the relative complexity of the seal assembly itself. Hydraulic gear pump and motor failure analysis and repair. The seals are arranged by shaft size from smallest to largest. However, the seal can be exposed to a wide variety of operating conditions, which can cause issues down the line. Mechanical seal failure phenomenon and analysis pump mechanical seals are available in a wide variety of models, there are five main leak points. Certain component failures of a centrifugal pump, such as coupling, hydraulic, static joints, and bearings, will cause the whole system to fail, but.
Improperly installing the mechanical seal will cause damage to elastomers orings or boots, along with a wide variety of other issues, as pictured to the right. Diagnosing common causes of sealing failures peerless pump. Table 1 shows the result of weibull analysis for mechanical seal of ngl pumps. The simple seal system incorporates an orifice in the flush line from the pump discharge to the mechanical seal. In the following, examples of common causes of failure of mechanical shaft. Failure of the mechanical shaft seal is the most common cause of pump downtime. In the meantime, here are a few of the most common causes of pump seal failure. In these applications, the mechanical seals can serve as. In spite of advancements in mechanical sealing technology, seal failures are still the most common cause of pump repairs. Mechanical seals and oil channel inserts are used to control the oil and block it from leaking. The most common cause of pump downtime is a mechanical seal failure. A mechanical seal can easily leak or become damaged if you let your pump or machine run dry.
Leakage leaks caused by mechanical failures can be catastrophic. Possible causes of mechanical seal failures by william forsthoffer on december 10, 2014 to ensure reliable, troublefree operation for extended periods of time, the seal must operate in a properly controlled environment. The manufacturer listings are alphabetical, refer to pages 7. A mechanical seal, figure 1, consists of a stationary member seat. Fill and vent pump before start up check material selection, at phvalue failure will normally occur at approximately 6month intervals regardless of the type of seal or bearing installed. In a horizontal, end suction centrifugal pump, frequent and regular seal failure with different seals indicates an undersized shaft subjected to excessive deflection. Pdf this article discusses a unique failure mode for double mechanical. Failurl modee s of centrifugal pum p assemblies failure mode failure cause failure effect. Incorrect selection of seal materials pump allowed to run dry.
The mechanical seal is the shaft seal device of the centrifugal pump, which has the advantages of small leakage and long life. Mechanical seals are designed to overcome these drawbacks. End face mechanical seals can incorporate many designs and. Its purpose is to limit the injection flow rate to the seal and to control pressure in the seal chamber.
The pump, piping, baseplate, mechanical seal, seal support systems, coupling, and driver are all integral parts of the pumping system. The fluid we are pumping is causing the elastomer to stick to the shaft. Maintenance and troubleshooting of progressing cavity pumps chad huskey moyno tech eng. The overwhelming reason for a pump to enter the shop is because of failure of the mechanical seal or packing, yet very few companies are regularly. The effects of mechanical seal failure on centrifugal pumps. Dry running at start up of pump, insufficient venting faces dull and with traces, selective corrosion observations. Mechanical seals can be very sensitive because the faces are incredibly flat. Below are two case studies pertaining to mechanical seal systems, a vital component of pumps operating in running process plant. In chemical production, it is often necessary to transport fluid from a low point to a high point, from a low pressure to a high pressure, or along a pipeline to a remote location.
Mechanical fuel pumps basic information and troubleshooting. 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. There are many different designs of a mechanical seal to meet specific applications. Vibration there are several causes of vibration which can damage seals or internals and cause pump failure.
Analysis of a mechanical seal failure reliabilityweb. Usually there are many symptoms, which signal a failure situation and are generally termed as potential failure modes. Root causes can include a plugged suction strainer, loss of level in the suction drum or a possible valve issue. Mechanical seals are precision designed and manufactured products, yet one of the most common causes of failure in positive displacement pump types is due to the malfunction of its mechanical seal. Hydraulic gear pump and motor failure analysis and repair guide page of. Mechanical seal leakage in pumps how much, if at all, mechanical seals do, must or must not leak is a controversial subject for which there are few clear answers. The materials of seal construction, particularly the sealing faces and elastomers. Click here for full pdf version of this article includes all graphs, charts, tables and author information.
But more important is to understand how pump failure modes arise and what to do to remove the pump failure root causes. Vibrations and misalignment will cause this seal type to leak. Failure modes of a mechanical seal can be identified by three main causes of failure. Checklist of problems vvith centrifugal pumps and their causes. Sleeve shaft wear when mechanical seals fail, they tend to spin on the shaft, or shaft sleeve. Failure of mechanical shaft seals the knowledge link. Therefore, seal related repairs are an excellent area in which to concentrate pump reliability improvement programs. Typically in a moyno pump the cause of cavitation is a lack of suction volume.
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