Rotary Mechanical Seal
A rotary mechanical seal is a device designed to prevent the leakage of fluids or gases from a rotating component (for example, the shaft of a pump, compressor, or reactor), while at the same time ensuring internal pressure containment and protection against the ingress of external contaminants.
Unlike traditional packings, mechanical seals provide greater efficiency, reduced leakage, and longer operating life.
Basic Structure
A mechanical seal is composed of several main elements:
- Seal faces (rotating and stationary): the two main rings, one attached to the shaft and the other to the pump casing. They are made of wear-resistant, low-friction materials (graphite, silicon carbide, tungsten carbide, technical ceramics).
- Elastic elements (O-rings, bellows, diaphragms): ensure static sealing and allow adjustment of the seal faces.
- Springs or spring sets: apply the necessary force to keep the seal faces in contact even when no pressure is present.
- Lubrication/cooling system: may be internal or external (API flush plans) to ensure proper operation and prevent overheating of the surfaces.
Operating Principle
The operation is based on the contact of two extremely smooth surfaces (rotating face and stationary face) separated by a very thin fluid film.
- This film reduces friction and prevents direct metal-to-metal contact.
- The pressure of the pumped fluid or of an auxiliary fluid helps maintain the sealing film.
- A precise balance between spring force, fluid pressure, and friction ensures seal stability.
Main Types
- Balanced and unbalanced seals: balanced seals withstand higher pressures with lower friction.
- Single and double seals:
- Single: used for clean, non-hazardous fluids.
- Double: used for toxic, abrasive, or highly volatile fluids (with a pressurized clean barrier fluid).
- Cartridge seals: pre-assembled, easy to install and replace, reducing the risk of assembly errors.
- Metal or elastomer bellows seals: provide flexibility and compensate for misalignments.
Main Advantages
- Significant reduction of leakage compared to packing.
- Longer service life and operational reliability.
- Lower maintenance costs.
- Suitable for corrosive, abrasive, or high-temperature/pressure fluids.
- Improved energy efficiency of the system.
Typical Applications
Water treatment and water sector
- Multistage centrifugal pumps for booster sets in civil and industrial water networks
- Submersible pumps for wells and lifting stations
- Agricultural irrigation systems (drip, sprinkler, pivot) with vertical and horizontal shaft pumps
- Desalination plants (high-pressure pumps for reverse osmosis)
- Sewage and wastewater pumping stations, with special seals resistant to suspended solids and abrasives
- Firefighting pumps and emergency systems
- Booster sets for residential, commercial, and hospital buildings
Chemical and petrochemical industry
- Process pumps for corrosive and toxic fluids
- Chemical reactors and agitators
Power and nuclear plants
- Boiler feed pumps
- Cooling water circulation pumps
- Compressors and auxiliary turbines
Paper and pulp industry
- Process pumps for pulp slurry
- White water circulation systems
Food and pharmaceutical industry
- Sanitary pumps for potable water and process fluids
- CIP (clean-in-place) systems with cleaning and sanitizing liquids
Marine and offshore industry
- Engine cooling systems
- Bilge water treatment systems
