pump seal failure and leakage is one of the most common reasons for pump downtime, and can be caused by a number of factors. To avoid pump seal leakage and failure, it is important to understand the problem, identify the fault, and ensure that future seals don’t cause further pump damage and maintenance costs. Here, we look at the top reasons pump seals fail and what you can do to avoid them.
Pump mechanical seals are the most critical component of pumps. Seals prevent the pumped fluid from leaking and keep any potential contaminants out.
They are used to move a variety of liquids in industries such as oil and gas, power generation, water and wastewater, food and beverage, and more. With such widespread usage, it is essential that leakage is identified, and prevented moving forward.
It should be acknowledged that all pump seals leak; they need to, in order to maintain a fluid film over the seal face. The purpose of a seal is to control the leakage. However, uncontrolled and excessive leaks can cause vital damage to the pump if not quickly fixed.
Whether seal failure is the result of an installation error, design failure, wear, contamination, component failure, or can unrelated error, it is imperative to diagnose the issue in a timely manner, to determine whether new repairs or a new installation is needed.
By understanding the causes for the most common types of pump seal failure, and with some simple tips, guidance and planning, it becomes far easier to avoid future leaks. Here is a list of the most common reasons for pump seal failure:
Installation error
When diagnosing a pump seal failure, the initial startup process and seal installation should generally be checked first. This is the most common cause of seal failure. If the right tools are not used, the seal has existing damage or the seal is not installed in the right direction, the pump will quickly become damaged.
Installing the pump seal incorrectly can cause a host of failures, such as elastomer damage. Due to the sensitive, flat face of a pump seal, even the smallest bit of dirt, oil or fingerprints can lead to misaligned faces. If the faces are not aligned, excess leakage will penetrate the pump seal. If larger components of the seal – such as bolts, lubrication, and support system configuration – are not also checked, the seal is unlikely to operate properly from installation.
The most common causes of improper seal installation are:
• Forgetting to tighten set screws
• Damaging the seal faces
• Incorrectly using piping connections
• Not tightening gland bolts evenly
If not recognised prior to starting the pump, an installation error can result in the motor tripping and the shaft twisting, both of which cause orbital movement and internal parts coming into contact. This will ultimately result in seal failure and a limited bearing life.
Selecting the wrong seal
Lack of knowledge during the seal design and installation process is another common cause for seal failure, so selecting the correct seal is crucial. There are many factors to consider when selecting the correct seal for a pump, such as:
• Operating conditions
• Non-process activities
• Cleaning
• Steaming
• Acid
• Caustic flushes
• The potential for off-design excursions
The seal’s material must be compatible with the fluid inside the pump, or the seal may deteriorate and lead to damage beyond fluid leakage. One example is choosing a seal for hot water; water above 87°C is unable to lubricate and cool seal faces, so it is important to select a seal with the correct elastomer materials and operating parameters. If the incorrect seal is used and the pump seal is compromised, the elevated friction between the two seal faces will cause certain seal failure.
The chemical incompatibility of a seal is often overlooked when selecting pump seals. If a liquid is incompatible with a seal, it can cause the rubber seals, gaskets, impellers, pump casings and diffusers to crack, swell, contract or deteriorate. Seals often need to be changed when switching the hydraulic fluid inside a pump. Depending on the pump’s liquid, a seal made of new, specialty material may be required to avoid failure. Every fluid and pump design has its own requirements. Selecting the wrong seal will ensure specific application challenges and damage.
Dry running
Dry running is caused when a pump operates without fluid. If internal parts within the pump, which rely on pumped liquid for cooling and lubrication, are exposed to increased friction without enough lubrication, the resultant heat will lead to seal failure. Most dry running failures occur by restarting the pump after maintenance without checking that the pump is completely filled with fluid.
If a pump runs dry and the heat raises beyond what the seal can manage, the pump seal will likely accrue irreversible damage. The seal may burn or melt, causing fluid to leak. Just a few seconds of dry running can cause heat cracks or blisters to the seal, which will lead to a leaking pump shaft seal.
In extreme instances, when a mechanical seal experiences thermal shock, it can shatter within 30 seconds or less. To prevent this particular kind of damage, check the pump seal; if the seal has been dry run, the seal face will be white.
Vibrations
Pumps inherently move and vibrate. However, if the pump is not properly balanced, the machine’s vibrations will increase to the point of damage. Pump vibration can also be caused by improper alignment and operating the pump too far to the left or right of the pump’s Best Efficiency Point (BEP). Too much vibration leads to the large axial and radial play of the shaft, causing an incorrect alignment, and more fluid leaks through the seal.
Vibrations can also be the result of excess lubrication; a mechanical seal relies on a thin film of lubricant between sealing faces, and too much vibration prevents the formation of this lubricating layer. If a pump needs to work in heavy-duty conditions, such as dredge pumps, the seal used needs to be capable of handling above-average axial and radial play. It is also essential to identify the pump’s BEP, and ensure that the pump is not greater or lower than its BEP. This may cause numerous forms of damage beyond seal leakage.
Bearing wear
As the pump’s shaft rotates, the bearings will wear due to friction. Worn-out bearings will cause the shaft to swing, which in turn causes damaging vibrations, the consequences of which we have discussed.
Wear is likely to naturally occur over a seal’s lifespan. Seals naturally wear over time, though contamination often speeds up wear and decreases longevity. This contamination may occur within the seal support system or internally within the pump. Some fluids are better at keeping contaminants from the pump seal. If there is no other cause for the seal wear, consider changing fluids to improve seal lifespan. Similarly, higher quality bearings are less likely to become deformed by load pressure, and so it is important to decrease the kind of metalto-metal contact that may cause practical contamination.
Post time: Mar-17-2023