If you know the symptoms of worn seals, you can know when to change them. Luckily, there are hydraulic seal kits available for most makes and models you may own. However, not all hydraulic seal kits are equal. Therefore, you must know what to look for in a hydraulic seal repair kit. This blog post will tell you the questions to ask and the answers you need to find.
Please visit our website for more information on this topic.
For the purposes of this article, we will be discussing the dynamic seals in your hydraulic system. Before we get into it, here’s a quick refresher on the two different types of seals.
Static seals are the seals between components that are not in motion, like the cylinder bore and the end cap. This is a static joint. It doesn’t move. Static seals tend to last a long time.
Dynamic seals are seals that move against another component. The seals in a piston, contained within a machined groove, move up and down the cylinder bore under the force of hydraulic fluid. They form the barrier between the outer diameter (OD) of the piston and the inner diameter (ID) of the cylinder bore. There are also rod seals contained within the gland, which are stationary. Under pressure from the fluid in the cylinder, the rod moves up and down against the rod seals. In both cases the seals prevent fluid and pressure from escaping the pressurized chambers in the cylinder bore.
In terms of items on a hydraulic cylinder that wear, seals have one of the shorter lifespans. Most other components are made from machined steel or other durable materials. Seals are made from pliable materials, mostly thermoplastics and rubber. They serve as barriers, containing the enormous pressures that build up inside the hydraulic cylinder– sometimes as much as 10,000 PSI. Seals often fail before other components, in part due to the tremendous stress they experience and in part due to their less durable nature.
With this in mind, you should perform hydraulic cylinder inspection and maintenance regularly, paying special attention to seals. Failure to detect and replace worn seals typically results in one of two things happening:
Loss of Pressure, Power, and Efficiency
Decreased hydraulic pressure will eventually affect the quality of whatever process the system is powering. The large hydraulic cylinders that raise and lower the blade or bucket of a bulldozer carry heavy loads of soil or rocks. If those cylinders have worn seals, the ability of that bulldozer to carry or move material is compromised. Failure could even endanger lives. Other industrial applications, including marine, transportation, aerospace, aviation, etc., all rely on reliable, consistent hydraulic power to move components, open gates, lower and raise landing gears, and activate other processes.
Risk of Damage to Other Components
A worn seal will eventually fail, allowing direct contact between the piston and the cylinder, or the rod and the gland holding the rod seal. At this point run the risk of scoring surfaces beyond repair. Parts might even seize and become immobile. Failure to replace worn seals can jeopardize the entire hydraulic cylinder assembly, with the potential to render it unusable.
There are a few signs to look out for which may indicate that you need to inspect and replace your hydraulic seals.
A specific type of leak called “weeping” occurs at the front of the cylinder bore where the rod comes out on its downstroke. In outdoor applications and factory environments with debris and manufacturing dust, this leaking fluid will attract these loose particles and the assembly will become very dirty. This is an obvious sign that it may be time for a seal repair.
Often, the loss in pressure is gradual and, at first, unnoticeable. If part of your hydraulic maintenance program involves a regular system pressure check, you will see this gradual pressure loss in your records. If you don’t do regular pressure checks, you are unlikely to notice this pressure loss until processes slow down to the point that operation is unsustainable.
Worn seals can also cause undue wear on pistons, cylinder bores, glands, rods, and other components. The damage to the seal could potentially come from metal shavings that get into the cylinder and work their way into a position where they can damage the seals, the piston’s OD, or the bore’s ID. Sudden events such as pressure spikes and power failures can also damage seals.
Another indicator that the seals are either worn or damaged is when the hydraulic system starts behaving erratically, characterized by jerking or inconsistent movements. This results in a loss of power or a lack of precision in whatever action your hydraulic system is powering. A well-functioning hydraulic system should run smoothly.
One of the tasks in replacing seals is determining that you have the best hydraulic seal kit available for your particular cylinder. Once you have determined that the seals in your hydraulic system need replacing, you should consult the owner’s manual to verify the specifications of the seals. Here are some things to look for as you evaluate your options:
The components in hydraulic cylinders are machined to critical tolerances. In order for the seals to perform as intended, they must also meet these critical tolerances. Many hydraulic cylinder seals are so exact that they are machined using CNC spindles.
There are many materials used for hydraulic seal kits that can operate in temperatures ranging from -128° – 260°C. Be sure to match the material with your application. Be careful to also ensure that the replacement seal material is compatible with the hydraulic fluid in the system.
Disassembly of a hydraulic cylinder is a challenging task. If you must replace a seal, it is prudent to replace them all—primary seals, secondary seals, wear rings, wiper seals, scraper seals, and anything else. Ensure that the hydraulic seal kit you purchase is as complete as possible.
Depending on their application, seals have different profiles, including U-seals, O-rings, V-rings, and others. Ensure profiles in the hydraulic seal kit match those specified by the OEM.
Sometimes this is not possible. Your hydraulic system may be custom designed or is a discontinued but still functional model. Many specialty seal manufacturers can provide the hydraulic seal kits you require as long as you can give them the correct specifications and dimensions.
Just as important as using the correct seal replacement kit, it is also essential to install the seals correctly. Here are some guidelines:
Make sure your supplier is a reputable company that can provide you with the correct hydraulic seal kits and valuable information on how to properly install the seals. Linde Polymer serves the hydraulic industry and we offer a full range of seals and seal replacement kits. We also have the technology, materials and knowledge to manufacture replacement seals for all your hydraulic machinery, systems and needs.
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.
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.
Link to Cigma
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.
If you are looking for more details, kindly visit Hydraulic Seals & Spare Parts.