Inside of your hydraulic cylinders, there are a number of seals that perform important functions, keeping your cylinders working efficiently while protecting internal components from being damaged by contaminants, corrosion, and other factors. These often-overlooked components are one of the most important parts of your hydraulic system — in fact, without those seals, your systems wouldn’t work at all.
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While you’ll almost never see these hydraulic cylinder seals during operation, it’s important to be familiar with the different types of seals that your machines use. When you know the function of each seal, as well as the differences between the materials used to fabricate hydraulic cylinder seals, you’ll ensure that your equipment will not only be best suited for its intended function but that it will also stand the test of time.
Hydraulic cylinder seals can be divided into two large categories: Static and dynamic. Static seals are used in situations in which the component parts aren’t designed to experience relative movement. These seals include O-rings, D-rings, backup seals, and other seals that are intended to remain in a fixed relative location.
One kind of static seal is usually found where the piston and the rod join. A static piston seal sits within the piston with the rod running through it. The pressure from the rod creates an impermeable seal that prevents hydraulic fluid from being pushed through to the other side of the piston. This is especially important in single-action pistons, which only have hydraulic fluid on one side of the piston.
Dynamic hydraulic cylinder seals, on the other hand, are intended for areas in which there is relative motion between two components. Because there are a number of different functions performed by dynamic seals within your hydraulic cylinder, it’s probably best to look at some of the specific seals you’re likely to come across in greater detail.
Piston seals provide the power for your hydraulic cylinder by preventing hydraulic fluid from flowing past your piston. This makes piston seals one of the most important hydraulic cylinder seals in your system.
The seal formed by a piston seal keeps contact between the piston and the cylinder bore, helping to control the motion of your cylinder and keeping your cylinder at the same position when at rest — even when it’s under a load.
Piston seals can be either single- or double-action. As mentioned earlier, a single-action piston has hydraulic fluid on only one side of the piston, which means that the piston seal must remain extremely close to the bore, otherwise fluid can seep through and lessen the effectiveness of your cylinder.
Double-acting cylinders, as the name implies, have hydraulic fluid on both sides of the piston. Because of this, the shape of a double-acting piston seal is symmetrical, possessing the same sealing properties in both directions.
These seals can also allow for more clearance between the piston and the cylinder bore, as they are not designed to prevent fluid leakage.
Rod seals perform two seemingly contradictory functions. First, they keep hydraulic fluid from leaking outside of the cylinder during operation. However, these seals are also responsible for ensuring that there is a thin layer of lubrication on the piston rod. This not only prevents corrosion but also lubricates other important parts of your cylinder.
Depending on the duty level of your cylinder, you may or may not also have a buffer seal, which is set further within the cylinder, past the rod seal. These hydraulic cylinder seals are intended to smooth out the pressure within your cylinder, preventing pressure peaks resulting from external factors. They also prevent any contaminants within the cylinder, such as metal flakes, from causing damage to your rod seals.
Sometimes referred to as dust seals, excluders, or scrapers, wiper seals protect your equipment by preventing contaminants from entering your cylinder as the piston rod retracts.
Since the piston rod is coated with a thin layer of fluid to prevent corrosion, it can also pick up dirt and other contaminants, which could quickly damage the interior components of your cylinder. Wiper seals keep these contaminants outside of your system.
These seals are intended to maintain moving parts in the proper position throughout the process of relative motion. In addition to keeping the important components properly aligned, guide rings prevent any metal-on-metal abrasion that might occur during operation, preserving the life of your equipment.
These seals also add another level of protection against contaminants by keeping your more sensitive seals safe from added wear.
Hydraulic cylinder seals can be manufactured from a number of different materials. Each material has different properties that make them better suited to different conditions, including high pressures and temperatures, as well as caustic chemicals. Here are the different materials you’re likely to encounter:
Rubber seals are used in situations that require a high degree of flexibility and compressibility. Nitrile butadiene rubber (NBR), fluoroelastomer (FKM), and hydrogenated nitrile butadiene rubber (HNBR) are all commonly used to fabricate dynamic cylinder seals. They possess good resistance to grease, mineral oils, and other hydraulic fluids.
Polytetrafluoroethylene (PTFE) offers superior durability under extreme conditions, including temperature, pressure, and caustic chemicals. PTFE also has a very low coefficient of friction, which means that it requires less lubrication than other seals and can actually function quite well in dry operation.
Encompassing a wide range of materials, plastic hydraulic cylinder seals offer moderate resistance to temperature and pressure, as well as chemical reactivity.
The durability of a plastic seal is largely dependent on the quality of the material itself, which can range from engineered plastics, which are superior to commodity plastic, to high-performance plastics. Because they have less flexibility than rubber or PTFE, these seals focus more on adding strength to your cylinder.
Thermoplastic elastomers, or TPEs, combine the strength of plastic with the flexibility of rubber, which means that they stand up to high use while also providing superior elasticity. These hydraulic cylinder seals are highly resistant to abrasion and tearing and will maintain a constant pressure for longer than other materials can.
Choosing the right seal is about more than materials, however. There are a number of external factors that you need to consider when you’re designing your cylinders. Each of these factors can go a long way toward determining which hydraulic cylinder seals you’ll need to ensure that your system can work efficiently for the long haul.
One of the most important considerations to keep in mind as you’re designing your hydraulic cylinder is to know precisely what you will need your cylinder to do. In general, you can break your application down into three different categories:
Having realistic expectations about the duty level that you’ll require from your cylinder will ensure that you won’t end up having to replace your equipment prematurely. If you’re unsure where your cylinder falls, or if you think you’re right on the dividing line between two service levels, it’s usually a good idea to choose a heavier-duty model — just in case.
You’ll need to know your average operating temperature, but also the temperature of your equipment when it’s at rest.
This is the speed at which your piston operates within your cylinder. Typically, the faster the cylinder operates, the hotter the cylinder will become.
It’s important to know what kinds of pressure your cylinder will encounter, which is usually expressed as a range. You’ll also want to identify any pressure peaks, noting both intensity and frequency.
There is a wide range of different hydraulic fluids available, and each fluid possesses a different viscosity, which will affect the hydraulic cylinder seals you’ll require.
The shape of your cylinder will also have an impact on which seals you’ll want to use in your cylinder. You’ll need to know the exact measurements of these parts:
Each of these factors will play a part in determining other considerations, including pressure, speed, and power. These can go a long way in helping you choose the right hydraulic cylinder seals to keep your equipment working properly.
No matter what your hydraulic system needs, MAC Hydraulics is here for you. Our team of experts can answer all of your questions about hydraulic cylinder seals. And our highly trained technicians will make sure that you get the information you need.
We’re always happy to offer you on-site repairs for any problems you encounter, as well as preventative maintenance to ensure your hydraulic systems continue working at peak performance.
We have extensive experience in a number of industries, including food and beverage, construction, manufacturing, and waste management. If you’re looking for a trusted partner to help you with hydraulic services, contact us today!
Piston seals serve as a pressure barrier and prevent fluid from passing the piston, which is important for controlling the cylinder motion or maintaining the position when at rest. Piston seals are typically classified into single-acting (pressure acting on one side only) and double-acting (pressure acting on both sides) seals.
Double-acting piston seals have a symmetrical profile and identical sealing functions in both directions. Typically, double-acting piston seals consist of a slide ring and an energizer. Because double-acting cylinders contain fluid on both sides of the piston, a relatively thick lubrication film can be permitted between the piston seal and the cylinder bore to minimize friction and wear.
A single-acting piston seal is designed for cylinders where pressure is applied from one side only. The piston in single-acting cylinders may have oil on the pressure side only, while the opposite side is open to atmosphere. Therefore, the piston seal must leave minimal oil film when passing along the cylinder bore since the transportation of oil otherwise would result in a leakage to the exterior.
In single-acting cylinders, the open end may push air out and draw air in as the piston reciprocates. This air may carry moisture and contaminants into the cylinder, which can lead to seal damage. Vent filters can be fitted to the open side of the cylinder to reduce contaminants entering the inside of the cylinder. The cylinder bore may also be hard chromium plated to prevent corrosion.
Wiper Seals
Hydraulic cylinders operate in a variety of applications and environmental conditions, including exposure to dust, debris, or outside weather conditions. To prevent these contaminants from entering the cylinder assembly and hydraulic system, wiper seals (also known as scrapers, excluders, or dust seals) are fitted on the external side of the cylinder head.
Wiper seals maintain sealing contact to the piston rod when the equipment is stationary (static, no reciprocating motion of rod) and in use (dynamic, reciprocating rod). Without a wiper seal, the retracting piston rod could transport contaminants into the cylinder.
Rod guides are typically placed inward of both the rod and buffer seal and should be lubricated on assembly with the same medium as used in the system. The guide must receive ample lubrication at all times and should not be outside the rod seal. However, in certain conditions, guides with polytetrafluoroethylene (PTFE) added may be used outside the rod seal due to their self-lubricating properties.
For more Hydraulic Dust Sealinformation, please contact us. We will provide professional answers.
Guide rings provide effective guidance of components that are in relative motion to each other and accommodate radial loads acting on the cylinder assembly. The selection of the right seal and guide for a given application requires consideration of many factors. Rod and piston guide rings prevent metal-to-metal contact between components, react to the radial load caused by side loads on the cylinder assembly, and keep the piston rod and piston radially centered in the cylinder assembly within acceptable limits for the seals. These functions are important for performance of the rod sealing system and piston sealing system.
Industrial seals are exposed to a wide range of challenging operating conditions such as high temperature, speed, pressure, and aggressive chemicals. To handle these and other harsh conditions, it is essential to select the most suitable sealing materials. Several factors impact material selection, including exposure to media, pressure, temperature, and potentially stringent regulatory requirements common in food and beverage or oil and gas applications. Types of sealing materials include:
Rubbers—NBR, FKM, and HNBR are commonly used rubber materials in hydraulic applications. They are extremely flexible and can be stretched and deflected by exerting relatively little force. Many of them deliver excellent resistance to mineral oils, greases, or other media.
Thermoplastic elastomers—These offers advantages typical of both rubber and plastic materials. SKF’s high-performance thermoplastic polyurethanes (TPUs) combine excellent abrasion and wear resistance, low compression set, and high tear strength and outstanding pressure resistance.
PTFE—Engineered to handle extreme conditions, PTFE and its compounds can withstand aggressive chemicals plus high temperatures and pressures. Due to their extremely low coefficients of friction, they can also tolerate dry running conditions.
Plastics—Plastic materials can meet higher temperature, chemical, and mechanical property requirements and can range from engineering plastics to high-performance plastics. Backup rings are typically made of plastics and used to enhance the pressure carrying capability of a rod or piston seal.
Designing sealing and guide systems in hydraulic cylinders requires careful attention to the interaction between all cylinder components and the operating conditions as well as the application requirements. The selection of the right seal profile and material for a given application requires consideration of many factors. For any application factors outside of the ordinary or to specify sealing systems in new hydraulic cylinder designs, a certain amount of expertise may be required.
Before seals can be selected, certain applications, parameters, and information should be collected. The following most common application considerations are almost always required when selecting hydraulic seals:
Fluid pressure range—the range of operating fluid system pressure, as well as frequency and severity of pressure peaks
Temperature range—the range of the fluid and cylinder assembly, both when operating and at rest
Speed—the stroking speed of the reciprocating piston rod
Fluid media—the type and viscosity of fluid used in the system
Hardware dimensions—the rod and bore diameters, seal groove dimensions and gaps (if already specified), cylinder overall length and stroke length, and surface finish specifications (if already specified)
Application of the cylinder—the type of equipment the cylinder will be used on and how the cylinder will operate in the equipment as well as installation, duty cycles, and environmental factors (external temperature or contaminants).
Performance issues in specific applications are not always solved with a standard or catalog range of products. For difficult and constantly evolving fluid sealing applications, seal engineers can develop a customized sealing solution. Development of this custom solution should include failure analysis and system operating conditions investigations, testing according to customer specifications and performance standards as well as technical training.
Hydraulic seals have a crucial impact on system performance in many applications. Factors such as temperatures, speeds, pressures, lubricants, and other application operating conditions can greatly impact seal life. Specifying the right seal helps boost machine performance, optimize operations,, and lower a machine’s total cost of ownership.
This material was contributed by Tadd McBride, Customized Molded Seals engineering manager at SKF. Click here to visit SKF’s website on hydraulic seals.
The Essential Guide to Hydraulic Cylinder Seals: Types, Materials, and Maintenance
Hydraulic cylinder seals are a big deal in the hydraulic industry, a hydraulic director once said this and he was right as without these there would be no hydraulics that work efficiently. These small, yet essential components make sure that the machinery is efficient and smooth in the day to day operation of every hydraulic system. This article will look at the world of hydraulic seals digging into the different types, materials, and the importance of maintenance and repair. But first, let’s get to know Completely Hydraulic, in this arena as they are the go-to experts for all your hydraulic needs.
Completely Hydraulic is a leading provider of hydraulic repairs, services, parts, equipment, and accessories for various industries. They offer maintenance contracts, hose repairs, and a 24-hour, 365-day call-out service to local areas of London, Kent, Essex, and Heathrow and their environs where their walk-in trade depots are situated. As specialists with expertise in bespoke projects, they cater to clients all over the UK.
In the world of hydraulics, seals are indispensable. Here are some common hydraulic seal types you may come across:
Many would not think that the choice of hydraulic seal materials is a big thing but it is, especially if you want to keep the machinery moving and for it to do its job for a long time. The most common materials include:
Discover more about the use of hydraulic seals and the seals for hydraulic equipment on the website.
Your machines need regular inspection or preventative maintenance, and some kind of repair protocol should your hydraulic equipment experience issues. Every business dreads the dreaded word known as ‘machinery downtime’ and just wants to focus on the extension of the life of the machine so that it can successfully do its job. Here are some common services offered by Completely Hydraulic:
FAQ’s
Q1: What are hydraulic seals used for?
A1: Hydraulic seals are essential components in hydraulic systems, used to prevent fluid leakage, maintain pressure, and ensure smooth operation between moving parts.
Q2: What are the most common types of hydraulic seals?
A2: Some common types of hydraulic seals include piston seals, rod seals, O-rings, wiper seals, buffer seals, and gaskets.
Q3: How do I choose the right hydraulic seal material for my application?
A3: The choice of hydraulic seal material depends on things like temperature, pressure, compatibility with hydraulic fluids, and the operating environment. Common materials include polyurethane, nitrile rubber (NBR), fluorocarbon (FKM/Viton), and ethylene propylene diene monomer (EPDM).
Q4: How often should hydraulic seals be replaced?
A4: Hydraulic seal replacement frequency depends on factors like usage, operating conditions, and the specific type of seal. Regular inspection and maintenance can help discover worn or damaged seals that need replacement.
Q5: How do I know if my hydraulic seals are failing?
A5: Hydraulic seal failure signs may include fluid leaks, reduced system pressure, excessive wear on cylinder components, or a decrease in equipment performance. If you notice any of these signs, you must address the issue promptly to avoid further damage.
Q6: Can I use the same hydraulic seal for different applications?
A6: While some hydraulic seals may work in multiple applications, you must choose the right seal type and material for each specific application to make sure you get the best out of your machinery.
Q7: Where can I find reliable hydraulic seals suppliers and manufacturers?
A7: Completely Hydraulic collaborates with leading hydraulic seals suppliers and manufacturers to provide high-quality products and services for various industries. Visit our home page to learn more about our offerings.
The world of hydraulic cylinder seals is sometimes complicated, but with the help of experts like Completely Hydraulic, you can discover an easy solution in this industry. When you understand the different hydraulic seal types, materials, and the importance of regular maintenance and repair, you can protect your investment and keep your hydraulic equipment running at its optimum performance.
FOR ALL HYDRAULIC SYSTEM ISSUES WITH A FAST TURNAROUND TIME IN THE UK CALL OUR EMERGENCY ON : 707 (24HOURS) WHEN YOU NEED US. YOU CAN ALSO VISIT THE FACEBOOK PAGE.
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