28 March, 2024

The importance of fluid sampling and preventative maintenance in hydraulic hose systems

13 April, 2017

By Matt Fielder, Condition Monitoring Market Development Manager, Parker HFFE.


Safe and reliable hydraulic systems are about far more than correct hose selection. Dependable installations that do not suffer from costly downtime are typically subject to organised and structured preventive maintenance programmes. Indeed, the best approach to preventing hydraulic system failures is being proactive in terms of inspection, maintenance and troubleshooting. Here, expert support and services from locally-based organisations such as ParkerStore can be the key to achieving long-term reliability and maximum uptime.

The importance of fluid sampling

Among the critical tools in any reputable preventative maintenance programme for hydraulic hose systems is fluid sampling, a practice that can save both time and money. Fluid sampling is able to identify potential problems that cannot be detected by human senses, and could cause major hydraulic or lube oil system failures.

A sampling process such as Par-Test from ParkerStore represents a complete laboratory analysis performed on a small volume of fluid. Customers can quickly analyse the test results of an individual sample and/or look at trend analysis for up to five different samples. Two types of kit are available, for water base fluid analysis or petroleum base fluid analysis. For both types, the test kit includes a pre-cleaned glass bottle, mailing container with pre-addressed label and sample information data sheet (to be filled out by the end user). Reports include particle count, photomicrograph, spectrometric, viscosity and neutralisation analysis. In addition, the petroleum base fluid analysis determines if the water present is beyond the saturation of the fluid, as well as a Karl Fischer test to give an accurate measure of water concentration in the sample fluid (measured in ppm).

With regard to particle count, results are reported over six different particle size ranges to the ISO 4406:1999 standard. The counts are per millilitre of fluid and the reporting is cumulative, namely the particle count in the >4(c)µm row includes the number of particles greater than 6, 14, 21, 38 and 70(c) µm, as well as particles between 4 and 6(c) µm in size.

For the photomicrograph (photo analysis), a small volume of fluid (20 ml) is magnified 100 times, which allows a quick glance at the contamination present in the fluid. Each line of the graduated scale represents 20 µm in size, while the full colour photomicrograph helps identify particles which would otherwise be grouped by class.

Viscosity is a very important property of a fluid in terms of system performance. It expresses the internal friction between molecules in the fluid. Typically, a breakdown in viscosity will be seen as an increase. Both SSU at 100ºF and cSt at 40ºC are reported.

Concerning neutralisation analysis, this titration test measures the acid level of the sample fluid and is referred to as the Total Acid Number (TAN). The production of acidic material causes oxidation degradation or aging of most fluids. This activity is promoted by elevated temperatures, the presence of entrained metal particles and intimate contact with air. It is the rate of increase of the TAN during any given period that is significant, not just the absolute value.

Regarding spectrometric analysis, results are obtained by a rotating disk electrode (ROE) spectrometer and reported in PPM. Some 20 different wear metals and additives are analysed to help determine the condition of the fluid. The spectrometric test is limited to identifying particles below 5-7 µm in size. Base line (new) fluid samples should be sent in for each different fluid to be analysed, which will be used to determine their status.

Of course, obtaining a fluid sample for analysis involves important steps to make sure a representative sample is collected. Erroneous sampling procedures will merely serve to disguise the true nature of system cleanliness levels. ParkerStore uses established and proven methodology for systems with and without a sampling valve.

Fluid sampling should be deployed as part of scheduled preventative maintenance programme as only this will help avoid expensive emergency repairs, downtime and safety risks for workers. The primary goal of preventative maintenance is to pinpoint weak system components before failure occurs. Such an approach delivers many potential benefits beyond system efficiency, including greater uptime, reduced repair costs, more effective use of maintenance staff and better control of spares inventory.

Safety first

Probably the most important aspect of any preventative maintenance programme is safety. With operating pressures as high as 700 bar, there are many potential dangers, not least pinholes, leaks, bursts, hose cracks, twisted hoses, cover blisters, bulges, soft spots, coupling blow-offs, whipping hoses and charged accumulators. Failures can have numerous consequences relating to fire risks and impact on mechanical and electrical equipment. With this in mind, the implementation of regular inspection intervals during routine operation, particularly in regard to factors such as operating temperature and pressure, is pivotal in ensuring that hydraulic systems run safely. Other giveaways include pools of accumulated fluid, low reservoir levels and greasy/dirty hoses.

The ability to troubleshoot is also paramount in the rapid resolution of issues before they become catastrophic failures. For example, an abraded hose should be re-routed to avoid rubbing on other hoses or abrasive sources. Where it cannot be re-routed, a suitable sleeve or pad should be fitted. Other factors such as excessive hose flexing should also be avoided to keep the hose from exceeding its minimum bend radius, thus avoiding bursts, while O-rings need to be checked to make sure that they have not degraded as a result of heat or temperature incompatibility.

Clearly, hoses that have become old, worn or damaged can present a danger to personnel and the environment, which makes regular inspection vital. As a result, daily inspection routines as part of a preventative maintenance programme might involve checking for damage to hose covers, hose hardness or stiffness, colour changes, squashed or kinked hoses, and fluid seepage. Maintenance personnel can check for fluid seepage by pushing at the base of the coupling with their thumb. Further maintenance routines conducted as part of a regular equipment shutdown, say once a quarter, could include hydrostatic pressure testing, for example.

There are of course many simple measures that can be taken to help maximise hose life and ensure worker safety. For instance, the maximum rated pressure of the hose should never be exceeded. Furthermore, hoses should never be over-bent or pulled by their couplings, while lifting a large diameter hose by its middle, with the ends dangling, can damage internal reinforcement at the support point.

Effective hose cleaning is also vital. The use of cleaning solutions, flushing or immersing in a cleaning bath, or steam cleaning, can all prove useful in prolonging hose life.

Summary

Ultimately, modern hydraulic hose systems must be backed by a reputable preventive maintenance programme, such as those offered by ParkerStore. Sure enough, selecting the correct hose is important, but the best practice approach to maximising hose life, minimising unwanted downtime and ensuring the safety of workers, is being proactive in the inspection, maintainence and troubleshooting of hose systems.

www.parker.com




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