Marine Mechanical Seals – Function, Components, and Benefits


The booster pumps are the prime driving force to support the engine operations in a marine vessel. These pumps supply high-pressure fuel from the storage bunker to the engine for combustion cycles. Consequently, pump operation is at risk of fluid leakage at the entry and exit points. Marine mechanical seals are robust and sturdy devices mandatory to prevent fuel oil leaking from these points. These seals are also installed in various centrifugal pumps, mixers, and other equipment on a ship.

In this blog post, we are providing an overview of mechanical seals and why they need regular inspection and timely replacement.

What are Mechanical Seals in Marine Equipment

The marine mechanical seal is a protective device located near the rotating shaft. It boasts an advanced structural design to securely retain the fluid and prevent leaking from the entry or exit point. This is vital when the stationary housing rotates around the rotating shaft.

The rotating shaft creates massive pressure within the centrifugal pumps when it enters the wet area. This action triggers the liquid to ooze out fast from the opening and closure points of the pump. Mechanical seals create a barrier at these positions to minimize leaking and wastage.

Marine Mechanical Seals – Primary and Secondary Components

Mechanical seals for the marine industry are available in various designs and configurations. This is necessary to match the specific equipment framework to optimize functionality and adaptability. From simple one-spring modules to complex cartridge seal designs, there are different versions of mechanical seals for diverse applications.

However, all mechanical seals have a few components and structures in common:

Gland Plate

The gland plate mounts and holds the seal assembly in its position.  


A set of O-rings and gaskets form the seal between the rotating shaft and the stationary housing.  


The vital component to induce load to the seal faces.

Stationary Components

These parts of the marine mechanical seals are connected to the pump housing and remain static during the pump operation. The stationary face or the seat ring is the prime stationary part and forms the seal interface.

Rotating Components

The rotating parts in this type of seal are located on the rotating shaft. This comprises a wear-resistant and sturdy rotating face a.k.a. the primary ring that rotates with the rotating shaft.

Mechanical Seals Vs. Gland Packing

There is often a dilemma when choosing between mechanical seals and gland packing for minimizing leakage in marine centrifugal pumps. Gland packing or compression packing system is a type of seal made of twisted or braided material. This type of seal was traditionally used to wrap around the rotating shaft to prevent fluid leakage.

Below is a comparison of the benefits of marine mechanical seals, addressing the drawbacks of classic compression packing seals.

Benefits of Installing Mechanical Seals in Marine Pumps

  • Minimal to no leakage from the pump casing during high-pressure pump operation
  • These seals are made of heavy-duty materials and operate seamlessly with corrosive fluids
  • The advanced design prevents friction between moving parts for durability and energy efficiency
  • Does not wear down the shaft or sleeves at little to no maintenance
  • Custom designs to suit diverse applications

Drawbacks of Gland Packing Seals for Pumps

  • Susceptible to wearing due to impact of abrasive fluids
  • Regular lubrication is essential to protect compression seals from damage.
  • These seals susceptible to misalignment during the rapid fluid flow and shaft rotation. It is necessary to adjust their position regularly to prevent leaking.
  • Seal-wearing can cause heavy leaking.
  • A water-cooling system is necessary to regular the seal temperature and prevent breaking.

Purchase High-Quality Mechanical Seals at Alfa Marine Spare Parts

Alfa Marine Spare Parts is a one-stop destination for OEM marine spare parts from Caterpillar, Cummins, Perkins, Scania, Wartsila, Doosan, Volvo Penta, and more.

Here are a few bestseller items on our web catalogue:

0132-0366 Cummins

3393035 Cummins

4960180 Cummins

Visit our category page to explore the entire range of marine seals in our inventory.

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