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Like all machines, hydraulic cylinders wear out. Every hour that a cylinder is in operation the forces of friction, pressure and corrosion contribute to a gradual decline in performance. As a hydraulic cylinder ages, it exhibits many clear signals that offer clues as to the forces acting on the cylinder and the overall condition of the unit. From hydraulic seals to wear patterns on chromed cylinder rods, every cylinder offers evidence that will give you advanced warning of a cylinder that may be about to fail. Symptoms may include abnormal noise; sticking or juddering; declining efficiency; loss of power / slow operation; increase in temperature and asymmetrical rod wear. These symptoms give advanced warning of a cylinder that is not operating optimally and may soon fail. Maintenance managers should be alert to any of these symptoms and schedule cylinders for repair before failure occurs.
Hydraulic cylinder failure happens when one or more of the components becomes worn to the point that it reduces the performance of the cylinder past acceptable limits. Since there are many components in operation within a cylinder, this creates many possibilities for failure. From seals to pistons, cylinder rods, barrels and mounting points, the various components are constructed from different materials and encounter different forces and conditions during operation. Thus, cylinder components may wear at different rates depending on the application and the environment in which they operate. Depending on which component fails, this can be a slow and gradual failure or a rapid, catastrophic failure. The most common causes of hydraulic cylinder failure are seal failure; fluid contamination; scored piston rods; bent piston rods; ballooned barrel tubes; scored barrels and split welds.
Hydraulic cylinder repair involves many different processes, skills and labour requiring knowledge, experience and sophisticated equipment. The standard procedure for hydraulic cylinder repair is Disassembly, Inspection, Sourcing replacement parts, Designing new components, Machining, welding & reconditioning, Chroming, Sandblasting & painting, Reassembly and Testing. Attention must be paid at each stage to ensure quality standards. Lack of diligence at any point or improper handling will result in a cylinder that does not perform correctly and at best has a shorter lifespan, at worst will fail very quickly. Reputable hydraulic cylinder repair centres will follow strict industry guidelines for repair and maintenance of hydraulic systems and adhere to Australian standards for quality.
Hydraulic cylinder seals are a component of the hydraulic cylinder responsible for the control and retention of hydraulic fluid. There are a number of different types of seals with any hydraulic cylinder, which have different roles. They fall into two main categories which are: Dynamic Seals and Static seals. Dynamic Seals move against other surfaces, while Static Seals remain fixed. The most common types of seals found in hydraulic cylinders are piston seals, rod seals, buffer seals and wiper seals. During hydraulic cylinder repair, each of these seals must be specially selected according to it's role and the application to ensure that it can deal with the kind of pressure, heat, and chemicals it will encounter in day to day operation.
Hydraulic seals should be replaced during every hydraulic cylinder repair. Seals are available in a range of materials with unique characteristics and properties. Some seal materials are able to withstand high temperatures, while others offer better friction coefficient properties. The correct material Seal material choice is extremely important for the lifespan and performance of your hydraulic cylinder seal and the cylinder itself.
The most common hydraulic seal types available are: Nitrile rubber, Hythane, Viton, Teflon, Polyurethane and Polymyte. During hydraulic cylinder repair, all worn seals must be inspected for evidence of premature wear or unusual signs of heat, pressure, friction damage or chemical erosion. If these symptoms are present, a different seal material should be selected to increase service life and performance of the repaired cylinder.
A leaking hydraulic cylinder seal is a sign is a sign of failure. The rod runs ‘wet’, with a collar of oil, there may be a dirt build-up around the gland as dust and debris settles on the damp area. Hydraulic seals fail for many reasons. Damage or misalignment may occur. Cylinder piston and bore clearances may exceed specifications. Heat degradation causes seals to harden, crack, lose elasticity and lose the ability to contain the hydraulic fluid. Premature wear may be caused by insufficient lubrication, rough surfaces or excessive lateral loading. Scarring can be caused by improper installation, or deep gouges on the chrome surface of the cylinder rod. Fracturing, or splitting of the seal due to sudden increases in high pressure. Chemical erosion due to exposure to harsh chemicals. During hydraulic cylinder repair all seals should be inspected for signs of wear and the root cause must be determined in order to rectify the contributing factors.
Hydraulic cylinder rods are coated in very hard chrome material in order to provide a durable, low-friction surface upon which the seal may run. As such, it is one of the components that is most susceptible to wear and damage. For this reason, industrial hard chrome plating of the cylinder rod is usually part of every hydraulic cylinder repair. Because the chrome plays such an important role in the proper operation of the hydraulic cylinder, it is good practice to re-plate the hard chrome surface during every repair to ensure the cylinder is restored to near-new performance.
The industrial hard chrome plating process is a highly technical one. First, the old chrome material is removed from the cylinder rod using electrolytic stripping or stone grinding. the cylinder rod is then placed in an electrolytic plating tank, which contains a special chromium solution. A current passed through the solution. Lastly, the freshly-plated rod undergoes a grinding and linishing process to restore the correct chrome thickness and surface finish.
During hydraulic cylinder repair, many components may be redesigned and re-machined to improve cylinder performance and longevity. In addition, due to the wide variety of hydraulic cylinders in operation today, it is often faster and more cost-effective to machine a new component than to source it from the manufacturer.
New parts are designed on sophisticated design software. Modern engineering software is capable of performing durability simulations which allow the engineer to verify the performance of newly designed components and make adjustments. Often this results in a component that performs better and lasts longer than the original part.
After design, hydraulic cylinder parts are manufactured using advanced, computer controlled CNC milling machines to ensure pinpoint accuracy. Although more simple parts may be milled using a lathe where appropriate, which is faster and less costly.
Hydraulic cylinder service exchange offers a faster way to get machinery back into service than the regular repair procedure. This service allows customers to swap out a worn / damaged cylinder for an off-the-shelf reconditioned cylinder of the same type. This is quicker than a standard repair because it eliminates much of the transportation time and the time spent waiting for components to be repaired or sourced from the manufacturer. In many cases, this reduces downtime to a day or two - or even a few hours if a suitable model is available for exchange from a nearby supplier.
Cylinder service exchange is generally no more costly, since customers usually pay only for repairs, however this is not true of all suppliers. While cylinder exchange is fast when available, cylinder availability can be an issue, especially for less-common cylinder models.
Preventative maintenance is critical to ensure the long term performance of your hydraulic cylinder. One of the major contributing factors in hydraulic cylinder wear is contaminated oil, which can become fouled by oil, debris or water. If these contaminants are not removed, they will increase friction, damage parts and seals and lead to premature wear and failure of the hydraulic cylinder. Therefore the best form of repair is to ensure that damage does not occur in the first place. For hydraulic cylinders, this means replacing filters according to a regular schedule of preventative maintenance. Clogged filter indicators are available for this purpose, which provide a way to visually inspect the condition of the fluid within the filter and replace the filter when it degrades. A clogged filter will allow dirt and contaminants to reach fragile components and cause premature wear and damage.