A centrifugal pump consists of several components, including a shaft and impeller, that create the force necessary to pump water. A mechanical seal is installed directly behind the impeller to help stop water from entering the machine’s parts. However, these shafts can sometimes crack or become damaged, forcing the need for replacement. It begs the question, “How do you replace mechanical seals?”

Causes of Mechanical Seal Failure

Before we go into the process of replacing mechanical seals, let us first understand what causes mechanical seal failure:

Allowing The Pump To Run Dry

Allowing your pump to run dry can damage a mechanical seal. Under the right conditions, mechanical seals can undergo thermal shock and break within 30 seconds or less.

Vibration

Pump vibration is induced by imbalance, improper alignment, or the pump operating too far to the left or right of the BEP (Best Efficiency Point) on the performance curve, among other things. Vibration harms your equipment, resulting in shortened seal life and damaged seals.

Hammering Couplings Onto The Shaft

Mechanical seal faces can be very fragile, and pounding couplings onto the shaft will cause seal damage.

Operator Error

Installation errors and skipping initial start-up procedures are big factors in mechanical seal failure. Improperly starting the pump can lead to the shaft twisting and the motor tripping, resulting in orbital movement and seal failure, internal parts contact, and shortened bearing life. Mechanical seals can be relatively sensitive because the faces are very flat. Even a small amount of oil, dirt, and fingerprints can align the faces.

How Do You Replace Mechanical Seals?

To replace the centrifugal pump’s mechanical seal, you’ll need a PVC saw, a new mechanical seal, a wrench, and some PVC glue and primer. Let’s get started.

Step 1: Turn off your power supply and pump, then cut the plumbing attached to the pump with the PVC saw. Remove your pump and place it in a workspace with ample room.

Step 2: Next, use the wrench to unscrew the pump’s bolts and housing, then remove the motor from the wet end of your pump.

Step 3: Hold the wrench tightly over the motor shaft, rotate the impeller clockwise, and then remove the seal from the back of the impeller and attach it to the shaft.

Step 4: Slide your new seal onto the shaft; make sure not to touch the front with your fingers; body oil can damage the mechanical seals.

Step 5: Hold the wrench firmly on the shaft to stop it from moving, and screw your impeller back onto the pump’s motor shaft. Line up your motor with the wet end of your pump and screw it back together.

Step 6: Reinstall the centrifugal pump and connect it to the plumbing using PVC glue and primer. Let the pump sit for a day before turning it back on to ensure the seal is firmly in place.

Signs You Need to Replace Your Mechanical Seal

Mechanical seals are exposed to various operating conditions, and if altered in any way, these conditions can cause catastrophic problems with the seal.

Deep Grooves On Seal Face

When you start noticing deep grooves on the seal face, inadequate lubrication may be to blame. However, these deep grooves could also be caused by abrasive materials in the process fluid, such as a slurry. When abrasives are embedded in the soft (carbon) face of the seal, it grinds a groove into the hard face of the seal.

Even Vs. Uneven Wear Track

An even worn track on a seal face usually indicates good contact between the mating seal rings. An uneven wear pattern usually indicates that the seal ring is distorted due to overtightening or excessive pressure. Other culprits for an uneven wear pattern could be elevated temperature or the hard face not being the hard face. Always review installation guidelines, techniques, and current operating conditions for running the proposal.

Cracked Seal Face

Thermal shock and mechanical seal impact are two reasons a seal face will fracture or crack. When tightening fasteners, try to avoid uneven or over-tightening. Maintain a consistent seal flush plan appropriate for the seal and process. Or eliminate the cause of the shock or impact.

Chips, Cracks In Seal Ring

Improper installation and mishandling of mechanical seal parts can cause chips and cracks in the seal ring. Always follow proper installation guidelines and avoid direct contact with brittle seal face materials.

Tips on Maintaining Your Mechanical Seal

Below are some things that you can do to guarantee a longer life for your pump seal:

Understand the Conditions

Pressure, speed, and temperature are all factors that can contribute to an increased leakage rate or a worn seal. Knowing your application conditions will help better select the proper mechanical seal.

The mechanical seal might perform steadily in fixed application conditions; nevertheless, if system variables are introduced, they might have drastic effects that can lessen your seal’s durability.

The published limits a seal can endure are more accurate for a continuous operation with more constant conditions. These limits are more precise than those of a cyclic operation.

Combining process variables produced varying degrees of conditions that a seal might need to adjust for, such as freezing, vaporization, or extreme heat that has to be dissipated. Applications that operate under higher temperatures, higher pressures, faster speeds, and thicker pumped fluid make maintaining a pump’s efficiency more challenging. A mechanical seal that’s more robust and resistant to condition changes might be the key to reducing repair downtime if you have a more difficult fluid-transferring process.

Know Seal Face Durability with Liquid

In most cases, the fluid being pumped is the lubricant for the mechanical seal. The fluids are susceptible to temperature and pressure changes depending on the application. Like the condition factors, the liquid is the primary variable, with vast degrees of chemical and physical states that must be understood. Liquids can range in thickness, purity, volatility, and toxicity and can even be explosive based on pressure, temperature, and chemical compatibility.

Deflection capabilities and greater seal face pressure decrease the chances of replacing or repairing the seal. Reducing the damage sensitivity can be attained by selecting the proper combinations. Hard/Hard mechanical seal faces are more suitable for dirty fluids but are vulnerable to greater damage if the fluid film is lost.

Hard/soft mechanical seal faces can endure longer after periods of lost fluid film before damaging seal faces. It is important to understand the limits to which the pump system will be exposed based on the application, how that will affect the liquid state, and how that seal can sustain expected performance.

Know the Cause of Seal Face Wear

Excessive leakage is often a symptom of a worn seal face. However, your pump may have more serious issues like bad bearings or a bent shaft.

Some seals also require a flushing system to remove the developed heat. Serious issues might occur if this process is interrupted or stopped.

Reduce Vibration

Deviating from this can lead to pump cavitation, which causes vibration and can deteriorate your seal. Operating at maximum flow can also damage the pump.

Excessive vibration can result in deterioration of components within the seal, like the O-rings, bellows, wedges, or polymer, or metal parts, like springs, set screws, or drive pins.

Proper Lubrication

Mechanical seals depend on the fluid film between the seal faces to lessen heat and friction. The fluid being pumped, in most instances, provides this lubrication as it interacts with the seal faces. Maintain your seal by not running in a dry run.

Reach Out to Us For More Pump Repair Tips & Products!

If you need a new replacement pump, our expert team can certainly help. Platinum Performance Products carries a vast inventory of new pumps, flow meters, motors, and control systems. We also provide preventative maintenance plans for those in need. To know more about our services, contact us today.