A mechanical seal is a device used to effect a seal between a rotating or reciprocating part and a stationary part. The use of the word seal is a misnomer, a mechanical seal is a restrictive flow path, this is either an angular or radial gap. The flow through this gap is generally so low it goes unnoticed if a liquid or inconsequential if a gas.
Mechanical seals can be designed to prevent contamination of the process by the environment and prevention of leakage of the process into environment.
The basic components of a mechanical seal are a Rotating Part and a Stationary Part. The primary seal of a mechanical seal consists of a rotating seal face and a stationary seal face. There is a very small gap between these 2 components which creates a restrictive flow path.
There are other components namely o-rings or gaskets which are used as secondary seals and hardware which is used to support the seal faces and to attach them to the rotating part (i.e shaft) and stationary part (i.e cover plate).
What are Mechanical Seal Faces?
The primary seal of a mechanical seal is made up of 2 seal faces where these two parts meet is where the seal gap is located. The mating surface of the seal face is machined to a very tight tolerance.
A seal face can be made from either soft or hard materials. A soft seal face is generally a wearing material.
What are the types of Mechanical Seals?
- Single Seal => it consists of one primary seal and it seals from process to atmosphere.
- There is always some leakage either to atmosphere or into process depending on the process pressure.
- Double Seal (Barrier) => consists of two primary seals in various arrangements. There is a barrier fluid between the two primary seals which is at a higher pressure than the process. There is always some leakage of the barrier fluid in process & out to atmosphere. As long as barrier pressure is maintained there is no leakage of process to atmosphere or contamination of process by environment.
- Double Seal (Barrier) – Wet => is a double seal where the barrier is a liquid. It is generally the most robust seal. It has a good pressure, speed and temperature capabilities.
- Double Seal (Barrier) – Dry => is a double seal where the barrier fluid is a gas. There are 2 specific types; Contacting and Non-contacting.
- Gas Contacting Seal – the seal faces are in contact, the soft face wear acts as a lubricant. Low pressure, speed and temperature capabilities and possibilities of wear getting into the process.
- Gas Non Contacting Seal – the seal faces are NOT in contact. They are kept apart by a flow of gas between the faces. Good temperature, speed and pressure capabilities. If operated correctly their is no wear but care must be taken in order to minimise shaft run out.
- Component Seal => is where both the rotating & stationary hardware are connected separately to the pump/mixer.
- Cartridge seal => is where the rotating and the stationary hardware are pre-assembled before mounting onto the pump/mixer. Cartridge seals are much easier to fit & maintain compared to the component seal.
What is a Barrier Fluid?
A barrier fluid is any fluid (gas or liquid) used to pressurise a double mechanical seal. It must be compatible with the process, generally non-toxic and a good lubricant.
What is a Mechanical Seal leak test procedure?
There are a number of bench test procedures for pressure testing mechanical seals, the most common one is API 682 which Flowserve use.
– API 682 – Pressurised seal to 25 psig.
– Maximum pressure loss is 2psi/5 mins.
How we can help you?
Flexachem provides a full range of Flowserve Mechanical Seals;
- Mechanical Seals for Pumps,
- Mechanical Seals for Agitators,
- Mechanical seals for hygienic and aseptic applications,
- Mechanical Seals for Power, Mining & Compressors,
- Sealing Supporting Systems – reservoirs, barrier systems, piston transmitters, gas panels, seal coolers, circulators and fill carts.
Flowserve heritage mechanical seal brands include:
Durametallic Seals specialist in Pharma, chemical and API seals.
Pacific-Wietz Seals specialist in Compressor and Pharma seals.
Borg-Warner Seals (part of BWIP – Borg-Warner Ingersall (Dresser) Pumps) specialist in API and gearbox seals.
Five-star Seals specialist in Pump seals and marine applications.
Pac-Seals specialist in OEM and specialty seals.
We supply mechanical seals into the pharmaceutical, bio-technology, chemical processing, mineral and ore processing, semi-conductor and general industries.
At Flexachem, we can also advise you on the appropriate selection of a seal support system which will deliver years of reliable service and help ensure operating cost savings in the long term.
If you have any query around the installation of mechanical seals or have some concerns around seal failures, why not contact one of our seal specialists below to discuss it in more detail and find out how we can help solve your issues and get your process running reliably again.
Contact our Mechanical Seal Specialists:
Chris Sheeran (External) – mob: 087 755 9936
David Walsh (Internal)
Tel: 021 4617260