30.11.2021

Mechanical Metal Bellow Seals come in different configurations, and each variant has its advantages and disadvantages. Among the most common variants are component mechanical seals and cartridge mechanical seals.


CARTRIDGE VS. COMPONENT MECHANICAL SEAL

When selecting a mechanical seal type, pump users must consider the cost of installation, long term running costs, pump characteristics, and the anticipated operational conditions (heat, vibration, and pressure). Keep your technical staff in mind as well, because having a skilled technician on-hand for regular maintenance vs. having to outsource maintenance and repairs makes a significant difference.

These factors will determine whether a component seal is preferable to a cartridge seal.


WHAT IS A CARTRIDGE SEAL?

A cartridge mechanical seal is a completely enclosed seal system with preassembled components. Typically, this seal type is composed of a gland, sleeve, and other hardware that make pre-assembly possible.

Refer to our blog post about different mechanical seal types for a more exhaustive list.

Advantages of Cartridge Type Mechanical Seals

The major benefits of choosing Cartridge Mechanical Seals for your pump seal system include:

Easy / Simple installation (No specialist necessary)

Higher functional security due to pre-assembled seal with fix axial settings. Eliminate measuring errors.

Eliminated the possibility of axial misplacement and resulting seal performance issues

Prevention of dirt entry or damaging of the seal faces

Reduced installation costs through reduced installation time = Reduced down times during maintenance

Potential to reduce the degree of pump disassembly for seal replacement

Cartridge units are easily repairable

Protection of customer shaft/shaft sleeve

No need for custom-made shafts to operate a balanced seal due to the internal shaft sleeve of the seal cartridge.



WHAT IS A COMPONENT SEAL?

Component mechanical seals are composed of separate dynamic and stationary parts. Unlike cartridge seals, Component Seals are not preassembled and require skilled technicians to install them. Incorrect installation of the seal faces, O-rings, and seal axial setting on the pump shaft will result in reduced seal life or in some cases, immediate seal failure.

Advantages of O-ring Mounted Mechanical Seals

The benefits of selecting non-cartridge seals for your mechanical seal support systems include:

Reduced expenses on initial seal purchase

Reduced spares costs as the individual components can be stocked vs. the entire seal

Superior adaptability to very small pumps


Common Pumps Seals are simply a method of containing fluid within a vessel (typically pumps, mixers, etc.) where a rotating shaft passes through a stationary housing or occasionally, where the housing rotates around the shaft.

When sealing a centrifugal pump, the challenge is to allow a rotating shaft to enter the ‘wet’ area of the pump, without allowing large volumes of pressurized fluid to escape.

To address this challenge there needs to be a seal between the shaft and the pump housing that can contain the pressure of the process being pumped and withstand the friction caused by the shaft rotating.


Before examining how mechanical seals function it is important to understand other methods of forming this seal. One such method still widely used is Gland Packing.

Gland packing is a braided, rope-like material that is packed around the shaft - physically stuffing the gap between the shaft and the pump housing.

Gland packing is still commonly used in many applications, however increasingly users are adopting mechanical seals for the following reasons;

The friction of the shaft rotating wears away at the packing over time, which leads to increased leakage until the packing is adjusted or re-packed.

The friction of the shaft also means that packing also needs to be flushed with large volumes of water in order to keep it cool.

Packing needs to press against the shaft in order to reduce leakage – this means that the pump needs more drive power to turn the shaft, wasting energy.

Because packing needs to contact the shaft it will eventually wear a groove into it, which can be costly to repair or replace.

Grundfos Pumps Mechanical Seals are designed to overcome these drawbacks.


Design

A basic mechanical seal contains three sealing points.

The stationary part of the seal is fitted to the pump housing with a static seal –this may be sealed with an o-ring or gasket clamped between the stationary part and the pump housing.

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