Chemical & Hazardous Applications
Mechanical Seal vs Mag Drive vs Canned Motor Pumps | ASW Engineering
Choosing the Right “Leak Strategy” Matters More Than People Think
Most pump failures don’t start with the motor. They start with leakage, vapour, heat, or wear around the sealing system.
If you’re pumping chemicals, solvents, hydrocarbons, hot liquids, or hazardous fluids, the choice between:
- Mechanical seal pumps
- Magnetic drive pumps
- Canned motor (hermetic) pumps
can be the difference between stable operation and constant maintenance.
This guide breaks down the differences in a practical, easy-to-understand way.
Option 1: Mechanical Seal Pumps (Most Common)
A mechanical seal is the standard method of sealing a rotating shaft where it passes through the pump casing.
Best for:
- Water and general industrial liquids
- Many oils and mild chemicals
- Applications where small leakage risk is acceptable
Pros:
- Widely available and cost-effective
- Easy to service and replace
- Works across a wide range of pump types
Cons:
- Seals wear over time (expected maintenance item)
- Can leak if run dry or exposed to vibration
- Not ideal for highly toxic/flammable fluids without extra protection
Common failure causes:
- Dry running (even for seconds)
- Cavitation/vibration
- Incorrect seal materials for the chemical
- Solids/abrasives damaging seal faces
Option 2: Magnetic Drive Pumps (No Shaft Seal)
Mag drive pumps use magnets to transfer torque from the motor to the impeller without a direct shaft penetration. This removes the mechanical seal entirely.
Best for:
- Corrosive or hazardous liquids
- Applications where leakage must be minimized
- Clean fluids with low solids
Pros:
- No mechanical seal = far lower leakage risk
- Reduced routine maintenance vs seal pumps
- Great for many chemical transfer duties
Cons:
- Not always ideal for liquids with solids/slurries
- Can be sensitive to overheating if run at poor conditions
- Some designs require careful operation to avoid internal wear
Typical applications:
- Chemical dosing/transfer
- Acids/alkalis (with correct materials)
- Solvents and process liquids
Option 3: Canned Motor Pumps (Hermetic / True Zero-Leak)
Canned motor pumps are fully sealed (hermetic). The motor and pump are integrated, and the liquid is contained within a sealed system—meaning no external shaft seal and no leakage to atmosphere.
Best for:
- Hazardous, toxic, or flammable liquids
- High safety requirements
- Operations where even small leakage is unacceptable
- Long-term reliability focus
Pros:
- True leak-free design (excellent for safety and compliance)
- Reduced environmental and exposure risk
- Ideal for high-value or dangerous fluids
Cons:
- Higher upfront cost
- Requires correct application and selection
- Maintenance is more specialised than basic seal replacement
Typical applications:
- Hydrocarbons and fuels
- Solvents and toxic chemicals
- Heat transfer fluids (depending on temperature)
- Chemical process plants prioritising containment
Quick Comparison: Which One Should You Choose?
If your main goal is “lowest upfront cost”
Choose: Mechanical seal pump
But accept that seals are a wear item and failures happen.
If your main goal is “reduce leaks and maintenance”
Choose: Magnetic drive pump
A strong middle ground for many chemical duties.
If your main goal is “zero leakage / maximum safety”
Choose: Canned motor (hermetic) pump
Best for hazardous and high-risk fluids.
Common Buyer Mistake: Selecting Only on Price
It’s easy to compare pumps on price, but the real cost is often:
- Unplanned downtime
- Seal replacement and labour
- Spill cleanup
- Product loss
- Safety risk and compliance issues
In many chemical applications, a more expensive pump can be cheaper over its lifetime.
What ASW Engineering Needs to Recommend the Right Pump
To recommend the correct sealing approach and pump type, we typically ask for:
- Liquid name and concentration (if chemical)
- Operating temperature
- Required flow and pressure/head
- Any solids content (and particle size if known)
- Hazard level (toxic, flammable, aggressive, etc.)
- Installation details (tank-to-tank transfer, circulation loop, etc.)
Need a Safer Pump Setup? Speak to ASW Engineering
If you’re unsure whether a sealed, mag drive, or canned motor pump is best for your application, ASW Engineering can guide you to the right solution and supply industrial pumps across South Africa and multiple regions in Africa.
We’ll help you choose a pump that doesn’t just “work on paper,” but works reliably in the real plant environment.
Disclaimer: This article is provided for general informational purposes only and does not replace professional engineering advice or manufacturer documentation. Always verify suitability for your specific application and follow site safety procedures. ASW Engineering can assist with pump selection and technical support.