Hydraulics health check
January 1st 2008

If you take the human body as a simple model for a hydraulics system, the brain would be the control unit with the heart as the pump, liver and kidneys as the filter, and joints as the actuators.

Using this analogy, alcohol destroying the liver would be a perfect example of how things can go terribly wrong within a system. Similarly within a hydraulic system, fluid contamination could cause disastrous results. Filtration weakness is a direct effect of a damaged or poorly maintained filter, and fluid transmission deteriorates dramatically when there's leakage or a blockage within the pipe work.

As with the heart, the pump's efficiency decreases when the pump is worn or the valves and seals are failing. With years, the human body grows and becomes older and so there is a chance of the joints failing – looking to the hydraulic system, actuator joint wear is a direct result of bearing wear caused by misalignment or load fatigue.

Using the human body as an analogy for a hydraulic system, it is clear to see that preventative maintenance is essential in order to ensure system efficiency, and over time is a cost-effective solution for sustaining system reliability.

Let us now take a look at some realworld models to see first-hand how preventative maintenance of hydraulic systems can be more efficient and costeffective.

Axial piston pumps and external gear motors invoke a combination of high power density and precision parts, generating several points of potential failure. Typical highly sensitive areas include: high load bearings, precision shafts and fulcrum points for the piston drive, high tolerance pistons and profiled piston rings, precision barrels and port plates, specially profiled shafts and gears and high tolerance housings. For cylinders, the critical areas to keep an eye on are the pistons, rods, seals and guide bearings, as well as the precision parts, such as the rod bearing and each of the primary, secondary and wiper seals.

As mentioned before, one thing that's often overlooked in a hydraulic system is the alignment of the actuators. Referring back to the human body analogy – a clean lift is achieved when you keep your back straight. Optimum performance results from actuator motions extended with the actuator placed on a straight line between the load bearing points.

When commissioning a hydraulic system, there are two potential risks to be aware of and get right. The first is the fluid choice; using the correct grade of fluid and following the recommended procedures for filling and priming the system is vital. Secondly, the products within the system should always be cleaned using specialised flushing equipment and adjusted according to low pressure, speed, rotation and direction.

Setting the system up and the use of conditioning equipment help ensure the system's integrity.

During operation the system should ideally be monitored constantly, paying particular attention to temperature, contamination and duty. At start-up, the system is usually cold and consequently the fluid is more viscous. This high viscosity often leads to poor priming resulting in cavitation and a sluggish response. Conversely, at high temperatures the viscosity is very low leading to poor lubrication of the system.

This poor lubrication results in poor working clearances and hardening of the seals that produce an unstable response to shock loads.

Preventing contamination within the system is a fine art, especially when you consider the environment where some hydraulic systems can be located.

Contamination can lead to wear of the system and can ultimately lead to abrupt failure, seizure or a control malfunction. Use of air breathers and actuator seals help prevent ingress, and care must always be taken during fluid replenishment.

For the system to function consistently, due care should be taken to achieve optimum adjustment with regular tuning and setting drift. If these fine adjustments are not carried out regularly, the system can overspeed, overload and overheat.

Under these circumstances, the lubricant can leak out and there is also a possibility of cavitation or fluid erosion.

You could have a reactive approach to maintenance where you're of the opinion – If it ain't broke don't fix it; only fixing the system once it's failed or when the operator notices strange noise. If you are bold enough to take this risk, you have to be prepared to dig deep into your pockets when the system breaks down. Predicative measures can offer a proactive approach to commissioning in real-time and optimised maintenance using real-time diagnostics.

There is a wide selection of condition monitoring tools available, targeted specifically towards hydraulics systems.

Portable diagnostic tools are used to measure levels of contamination, temperature, pressure, noise and vibration.

Trending tools are on hand once the operation of the system is defined to compare against defined responses such as definition of duty, definition of failure or wear limits, and definition of recognised characteristics.

Remote system monitoring is now available for the remotest of places. It is a real-time, wire free, intelligent, proactive monitoring system that works across a GPS data network. Rexroth's Remote System Monitor itself is a compact, multifunctional device that can be adapted to meet a wide range of monitoring tasks, where a rapid two-way flow of data is important. Typical applications include: activation and interrogation of hydraulic systems for diagnostic purposes and the relaying of virtually limitless amounts of data between sites.

Reliable, cost-effective service is part of Rexroth's complete Drive and Control package. The service and support of Rexroth's systems and products extend beyond basic purchasing. The Industrial Hydraulics division of Bosch Rexroth has 250 dedicated hydraulics personnel, providing customers with a variety of services to ensure that hydraulic products and systems keep running effectively and efficiently.

Rexroth's Centre of Competence in St.

Neots together with regional service facilities in Treforest, Bradford and Port Laoise, Ireland combine to present the hydraulics industry over 30 professional engineers with expertise and know-how in design, build, supply and service of hydraulic systems.

Whether it is hydraulic pumps, motors, valves, or cylinders, in stationary or mobile situations, Rexroth's engineers can configure the complete hydraulics system.

Computer-aided simulation programs allow Rexroth's engineers to determine the most technically advanced and economically efficient proposals, and the company's ongoing research and development guarantees future-proof development for all applications.

Past experience within numerous industries enables Rexroth to offer application-specific solutions, and implement monitoring and controls to achieve optimum performance. Up to and beyond commissioning, Rexroth ensures that the components specified are adaptable for any additional requirements identified.

To maintain this quality, Rexroth's service team is committed to adding value through service and support.

This includes supply of Bosch Rexroth genuine spares and a world-wide repair and maintenance service. Benefits consist of initial services including system installation and operational services comprising of plant modernisation and component repairs.

As part of its ongoing commitment to providing best-in-class after sales customer service, Bosch Rexroth has developed a range of training programs.

Effective training is an essential part of any job and allows for productive work as well as avoiding downtime and stoppages.

Whether it is training on specific components, maintenance procedures or entire projects, Rexroth can tailor your training requirements with its extensive range of courses created in conjunction with it's training partner The National Fluid Power Centre. Thus ensuring a professional and market leading delivery of all your training needs.

Rexroth's team of experienced service technicians are supported by fullyequipped repair workshops with state-ofthe- art repair test and diagnostic facilities.

This enables the engineers to troubleshoot the hydraulic system and recommend repairs that will get it back up and running quickly and avoid costly downtime. All sizes and types of hydraulic systems and components can be serviced, including overhauling, rebuilding projects, custom-designed maintenance programs and pressure oil testing.

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