What is a mechanical seal on a pump?

Introduction

Pumps are essential equipment in various industries, such as oil and gas, water treatment, and manufacturing. They are used to transfer fluids from one location to another, either vertically or horizontally. However, to ensure that pumps work efficiently, they need to be sealed to prevent fluid leakage. Hence, mechanical seals were developed to address this issue. Mechanical seals are critical components of pumps that help to maintain the seal between the rotating shaft and the stationary housing. This article provides an overview of mechanical seals on pumps, their types, and how they function.

What is a Mechanical Seal?

A mechanical seal is a device that prevents the leakage of fluids in rotating equipment, such as pumps, compressors, and mixers. It consists of two primary components: a stationary part that is fixed to the pump housing and a rotating part that is attached to the pump shaft. The stationary part is usually made of a hard material, such as ceramic, carbon, or tungsten carbide, while the rotating part is made of a softer material, such as carbon.

Types of Mechanical Seals

There are various types of mechanical seals based on their design and application. Here are some of the common types:

1. Pusher Type Mechanical Seals

Pusher type mechanical seals are the most commonly used mechanical seals in industries. They consist of a stationary part that is attached to the pump housing and a rotating part that is attached to the pump shaft. The rotating part pushes against the stationary part, creating a seal to prevent fluid leakage. Pusher type mechanical seals are suitable for pumps that handle clean fluids.

2. Non-Pusher Type Mechanical Seals

Non-pusher type mechanical seals do not have a spring mechanism to create pressure between the rotating and stationary parts. They rely on the fluid pressure to maintain the seal. Non-pusher type mechanical seals are suitable for pumps that handle viscous or solid-laden fluids.

3. Cartridge Mechanic Seals

Cartridge mechanical seals are pre-assembled mechanical seals that include all the components required for installation. They are designed for easy replacement and reduce the risk of incorrect installation or damage to the seal components during installation. Cartridge mechanical seals are suitable for pumps that require frequent seal replacement.

4. Split Seals

Split seals are mechanical seals that can be split into two parts, allowing for easy installation without removing the pump shaft. They are used in pumps that are difficult to disassemble, such as vertical pumps or pumps that are installed in confined spaces.

5. Metal Bellow Seals

Metal bellow seals are mechanical seals that use a metal bellows instead of an elastomer to maintain the seal. They are suitable for high-temperature or high-pressure applications.

How do Mechanical Seals Work?

Mechanical seals work by creating a barrier between the fluid being pumped and the external environment. When the pump is in operation, the rotating part of the mechanical seal spins with the pump shaft, while the stationary part remains fixed to the pump housing. The two parts of the seal are held together by a spring or fluid pressure, creating a tight seal. The seal faces, which are the surfaces in contact with each other, are lubricated by a liquid film to reduce friction and wear.

Maintenance of Mechanical Seals

Mechanical seals require regular maintenance to ensure their proper functioning and prevent fluid leakage. Here are some tips for maintaining mechanical seals on pumps:

1. Check the Seal Faces for Wear

The seal faces should be inspected regularly for signs of wear, such as grooves, scratches, or cracks. If the seal faces are worn, they should be replaced immediately to prevent fluid leakage.

2. Lubricate the Seal Faces

The seal faces should be lubricated with a suitable lubricant to reduce friction and wear. The correct lubrication will also help to reduce heat buildup, which can damage the seal faces.

3. Check the Spring or Fluid Pressure

The spring tension or fluid pressure that holds the rotating and stationary parts of the seal together should be checked regularly. If the tension is too low, the seal may leak, while if it is too high, it can cause excessive wear.

4. Inspect the Sealing Surface of the Pump Shaft

The sealing surface of the pump shaft should be inspected regularly for signs of wear or damage. If the surface is worn or damaged, it should be repaired or replaced immediately to prevent damage to the seal faces.

5. Store Seals Properly

Mechanical seals should be stored properly in a clean, dry environment to prevent contamination or damage. They should be handled with care during installation to prevent damage to the seal faces.

Conclusion

Mechanical seals are critical components of pumps that help to maintain the seal between the rotating shaft and the stationary housing. They prevent fluid leakage and ensure the proper functioning of the pump. There are various types of mechanical seals, such as pusher type, non-pusher type, cartridge seals, split seals, and metal bellow seals. To maintain mechanical seals, they require regular maintenance, such as inspecting the seal faces for wear, lubricating the seal faces, checking the spring tension or fluid pressure, inspecting the sealing surface of the pump shaft, and storing the seals properly. With proper maintenance, mechanical seals can provide excellent performance and prevent fluid leakage.