The often-forgotten and crucial component in a pump system is the mechanical seal, which prevents fluid from leaking into the immediate environment. Leaking mechanical seals due to improper maintenance or higher-than-expected operating conditions can be a hazard, housekeeping issue, health concern, or even an EPA issue. It is important to implement practices and conditions to ensure the proper operation and longevity of your mechanical seals to prevent leakage and subsequent downtime or safety hazards.
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Here are some things that you can do to ensure a longer life for your pump seal:
Pressure, temperature, and speed are all factors that can contribute to a worn seal or increased leakage rate. Knowing the application conditions will help better select the right mechanical seal. The mechanical seal may perform steadily in fixed application conditions, however, if system variables are introduced, they may have drastic effects that can reduce your seal&#;s durability. The published limits a seal can withstand are more accurate for a continuous operation where there are more constant conditions. These limits are not as precise with a cyclic operation.
Combining process variables creates varying degrees of conditions that a seal may need to adjust for such as vaporization, freezing, or extreme heat that needs to be dissipated. Applications that operate under higher pressures, higher temperatures, faster speeds, and thicker pumped fluid makes maintaining a pump&#;s efficiency more difficult. Having a mechanical seal that is more robust and resistant to condition changes may be the key to keeping repair downtime at a minimum if you have a more difficult fluid transferring process.
The fluid being pumped is in most cases is the lubricant for the mechanical seal. The fluids, depending on the application, are susceptible to temperature and pressure changes. Similar to the condition factors, the liquid is the main variable, with vast degrees of physical and chemical states that need to be understood. Liquids can range in thickness, purity, volatility, toxicity, and can even be explosive depending on the temperatures, pressure, and chemical compatibility.
Greater seal face pressure and deflection capabilities decrease the chances of having to replace or repair the seal. Lowering the damage sensitivity can be obtained by selecting the right combinations. Hard/Hard mechanical seal faces are better for dirty fluids, but vulnerable to higher damage if the fluid film is lost. Hard/soft mechanical seal faces can hold up longer after periods of lost fluid film before seal faces become damaged. It is important to understand the limits that the pump system will be exposed to based on the application, and how that will affect the liquids state along with how that seal can sustain expected performance.
Excessive leakage is typically a symptom of a worn seal face. There can be other more serious issues with your pump, such as bad bearings or a bent shaft.
If worn from abrasive contact, the rubbing edge of the seal will show signs of physical distress such as grooves and even chips. Some seals also need a flushing system to remove the heat that is developed. Serious issues may occur if this process is interrupted or stopped.
Try to operate your pump in its BEP (Best Efficiency Point). When you deviate from this it can cause pump cavitation This will cause vibration which can deteriorate the seal. Operating at maximum flow can be deadly to the pump.
Excessive vibration can cause deterioration of components within the seal such as the O-rings, bellows, polymer or wedges, or metal parts such as springs, drive pins, or set screws.
Mechanical seals rely on the fluid film between the seal faces to reduce heat and friction. The fluid being pumped in most cases provides this lubrication as it comes into contact with the seal faces. Maintain your seal by not operating in a dry run. Install a Dry Run Monitor or flow sensor that will alert users when there is not sufficient fluid within the system. Continuous applications tend to be more stable with mechanical seal reliability than cyclic applications for this exact reason.
Mechanical seals on average are rated to last a minimum of a span of two years. Obviously as stated earlier this is largely dependent on the variables, conditions involved, and the limits to which you run at. Knowing your system and how it will function and what to look for when problems occur can go a long way in maintaining a mechanical seal. Selecting the right one can be a time-consuming and complicated process, Anderson Process has the knowledgeable experts to help guide you towards providing a solution that helps your system perform at maximum efficiency.
Mechanical Seal failure often occurs, but why?
Here are 8 reasons for a Mechanical Seal failing within a process
Dry running is where a pump is operated without fluid. 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. Failure can happen in seconds and so it is always import to ensure the pump is completely filled with fluid prior to operation.
Tip: If a seal has been dry run, the face of it will be white, and to prevent dry running an AMP sensor can detect when high amounts of AMPs are being drawn and stop pump operation before too much damage occurs.
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Chemical Attack
Every material has its Kryptonite. If a liquid is incompatible with a fluid it can cause internal parts such as rubber seals, gaskets, impellers, pump casings and diffusers to crack, swell, contract or deteriorate.
Chemical compatibility tables outline which materials are compatible with which fluids rating them from Good to Poor. Whenever frequent pump wear occurs, or should pump failure occur after a short amount of time- this is one of the first items which should be checked.
Cavitation
Pumps are controlled by the system they operate in. If not restrained they can operate at performances which are damaging to internal parts &#; similar to driving a car downhill in first gear at speeds where the rev counter is in the red.
Operating a pump at the wrong parts of a performance curve, lead to accelerated part wear one of which can be the seal.
Excess Heat
Excess heat from high fluid temperatures can cause elastomers to swell or melt restricting its effectiveness leading to leakage.
High fluid temperatures not only originate from process but if fluid recirculation occurs for extended periods of time either due to operation against a closed valve or should fluid continue to recirculate through a relief valve, energy is transferred to the fluid causing heating of the fluid.
Incorrect Fitting
When a seal is installed it is designed to move with the shaft. Lateral and vertical movement is normal. If installed incorrectly then excess play can cause damaging forces to the seal. If too restricted the seal springs can snap or faces wear.
Shaft Movement due to bearing Wear
If a shaft has too much play, its lateral movements will cause the seal to absorb such forces rather than the bearings - something which it is not designed to do. High torsional forces can cause the seal to tear.
Worn Shaft or Wear
Certain elastomers such as Viton can increase shaft wear, meaning when a seal is replaced, it the shaft has a smaller OD reduced by friction over the years, then the seal will not fit tightly enabling fluid to leak.
Seals are specifically designed for a pumping process and should a seal encounter solid particles such as sand or silt which it is not designed to handle it can cause the forming of grooves in soft seal faces causing the seal to drip and leak the process medium. Installing a hard faced mechanical seal can limit and prevent this issue from reoccurring provided concentrations of solids are not above those specified at enquiry stage.
If you are frequently experiencing Mechanical Seal Failure, and are looking to eliminate this from your process, speak to us to see how we can help.
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