Question 1

What are hydraulic seals?

Accepted Answer

A hydraulic seal is a device or substance used between two or more components to prevent something from passing between them. They are found in many items in everyday use.

Why do we need seals?

Hydraulic and pneumatic cylinders operate by air or fluid being pumped into the cylinder at pressure. Because cylinders work at high pressure, there is lots of potential for air or fluid to escape between the different components, even through the very smallest of gaps.

Wherever the different cylinder components meet, if they are not welded, they will require sealing.

Types of hydraulic seals

There are six general types of seal that may be found in a hydraulic cylinder. They are:

Wiper, Scraper or Dust Seal
Rod Seal, Gland Seal or Neck Seal
Static Seal
Piston Seal
Wear Ring, Bearing Ring or Guide Ring
Rotary Seals

Where seals are positioned in a cylinder

The main purpose of a Wiper Seal in a cylinder is to prevent dirt and other contaminates from getting into the system. This is usually achieved by a wiping lip that points out of the cylinder.

Piston Seals are designed to seal between the piston and the cylinder, sealing dynamic pressure to allow the cylinder to extend and retract.

Rod Seals are designed to seal between the rod and the gland.

Rotary Seals as their name suggests, seal against a dynamic surface that is rotating.

Static Seals are a wide variety of seals that seal against only static surfaces.

Guide Rings prevent contact between two moving surfaces.

Different seals are classed as either single or double acting. A single acting seal is designed to take pressure from one side only. A double acting seal is designed to take pressure from both sides.

To suit the many different applications out there, sealing products are available in metric or imperial sizes, and can come in a wide range of standard and specialist materials.

Not all seals come ‘off the shelf’, some need to be custom made to suit the exact requirements of an existing application or for a new application that is being designed.

FPE Seals offer both, an extensive range of seals and seal kits in stock ready to order today, as well as a machined seals service, with a specialist team that can create made to order products.

If you have a sealing need or require any advice, contact our team today, we are more than happy to help.

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Question 2

What are Rotary Seals or Shaft Seals?

Accepted Answer

Rotary Seals also referred to as Shaft Seals, Oil Seals, or Lip Seals. Are designed to stop external contamination such as dirt, dust, water, and hazardous contaminants, from entering the moving parts, while retaining lubricant in the rotary applications.

The sealing effect is achieved by a garter spring which is normally used to ensure a constant force on the shaft. Rotary shaft seals are used between rotating and static machinery components.

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How Do Rotary Seals or Shaft Seals Work?

A rotary seal includes a sealing lip, a garter spring, and an external metal case. The sturdiness of the metal forms a rigidity and firm fix to the connecting components. The lip seal conducts the actual sealing function while the garter spring offers the required flexibility of movement. For vacuum applications rotary seals are designed differently and do not include a spring.

The basic design of the seal can be customised to suit specific requirements. These seals are extremely versatile and can be made of a variety of materials ranging from hard metals to plastic. The most common materials are steel, brass, silicone rubber, and EPDM.

Types Of Rotary Shaft Seals

There are different types of rotary shaft seals, each with its own specific design and materials. Some common types include:

Radial Lip Seals: These are the most common type of rotary seals. These seals are used in applications where the sealing surface is rotating relative to the housing. For low to high-speed applications, radial lip seals are designed in a wide variety of materials to best suit different fluids and temperature requirements.

V-Ring Seals: These are used for shafts that rotate in both directions. These seals are made of elastomer or rubber to prevent contamination from entering the shaft area and can handle high-speed applications.

Mechanical Seals: Mechanical seals are designed to seal against the rotating shaft using two flat surfaces. These seals can be made from a variety of materials including ceramic, carbon and metal and are typically used in high-pressure applications where a high degree of sealing is required.

Labyrinth Seals: Labyrinth seals are designed as a non-contact type of rotary seal which uses a series of grooves to create a curvy or tortuous path for the fluid or gas to flow through. These seals are effective at preventing contamination from entering the shaft area and are usually used in high-speed applications where there is a risk of fluid leakage.

Gland Packing Seals: They are typically used to seal a rotating shaft where the shaft passes through a stationary housing or casing, such as in a pump or a mixer. The packing material used in gland seals can be made of various materials such as graphite, PTFE, aramid fibre and carbon.

Choosing the Right Rotary Shaft Seal

For the proper functioning of applications, choosing the right rotary shaft seal is important. Several factors can affect the performance of rotary shaft seals, including:

Temperature: The performance and longevity of rotary shaft seal, can be affected by the operating temperature of the application, so choosing the right seal material is crucial.

Pressure: The pressure of the fluid being sealed can also affect the performance of rotary shaft seal, so it is essential that the seal chosen can withstand the pressure.

Speed: It is important to choose a seal that is designed for the appropriate speed range, so that the speed at which the shaft is rotating does not affect its performance.

Fluid type: Different fluids have different chemical properties that can affect the performance of the seal.

Benefits of Rotary Shaft Seals

Leakage Prevention: The primary function of a rotary shaft seal is to prevent leakage of fluids (such as oil, grease, or hydraulic fluid) from the housing or chamber where the shaft is rotating. By effectively sealing the gap between the rotating shaft and the stationary housing, these seals ensure that fluids stay contained within the system, reducing wastage and potential environmental hazards.

Contamination Protection: Rotary seals not only keep fluids in but also prevent external contaminants, such as dirt, dust, water, and other particles, from entering the system.

Friction Reduction: Using a well-designed rotary shaft seal can help minimise friction between the rotating shaft and the stationary housing and prevent wear on internal components, improving efficiency and reducing energy consumption.

Versatility and Reliability: Rotary seals come in various materials and designs suitable for different applications and operating conditions. They can be customised to manage a wide range of temperatures, pressures, speeds, and fluids.

Applications of Rotary Seals

Pumps: Rotary seals are used in pumps to prevent leakage of fluids such as water, oil, and chemicals.

Marine Applications: Used in applications such as propeller shafts, rudder shafts and thrusters to prevent leakage of seawater.

Food and Beverage Industry: Used in various food and beverage equipment to prevent contamination and ensure hygiene standards.

Pharmaceutical Industry: Used to prevent contamination and ensure product integrity.

If you require any further advice regarding Rotary Shaft Seals and their applications, our knowledgeable team at FPE Seals would be happy to help.

We stock, source, and supply a range of Rotary Seals. Can’t find what you’re looking for? We can also manufacture seals to your specification, in a full range of materials to meet your exact requirements.

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