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Within the hydraulic industry there are certain buzz words that are spoken regarding Hydraulic fluid cleanliness. Before we can talk about Hydraulic oil cleanliness, let us try to picture how small a “micron” really is.
Now we can see how small a micron is relative to a human hair, ISO (International Organisation for Standardisation) have conducted a controlled experiment to measure how clean our hydraulic oil really is. The ISO Code is used to display contamination levels per millilitre of fluid for 3 sizes, these are 4 microns , 6 microns and 14 microns. The ISO code is represented with 3 numbers (example 20/17/14). Each number represents a contaminant level code for the 3 particle sizes.
The ISO Cleanliness Code references the number of particles greater than 4, 6, & 14 microns in one millilitre of fluid. The corresponding ISO Range Code, shown below, gives the cleanliness code number for each of the three particle sizes.
As you can see from the table every ISO Code has a specific particle range which identifies the cleanliness of the fluid. From this table you can see that ISO Code 23 is twice as ‘dirty’ as ISO Code 22.
If you are wondering how we can measure these very small particles in Hydraulic fluid? There are a number of ways in which we do this we can use Particle counters these use a shadow graph type technology , as the oil passes through the light the particles are picked up by shadows , the machine can calculate the amount of oil and how many ‘shadows’ are in that amount of oil.
Now there are drawbacks from using such a particle counter, this type of method will only tell you there are a specific number particles in the system and will give you a ISO Code number, this will not tell you what the particles consist of.
How do you find out what the very small particles consist of? We can provide sample bottles and have these sent off to a lab to be tested in a more controlled environment. This will break down the components within the hydraulic oil and highlight anything irregular.
From the list of contaminants we can have an idea what state our hydraulic power pack is in, for instance a high number of Aluminium particles could indicate the pump is failing. Water can be a huge problem for hydraulic systems, not only for rust issues but as water contains oxygen it can be compressed, Hydraulics relies on transmitting power using an incompressible fluid also water under pressure can give up a vapour which when sucked up by the pump and pressurised can implode causing explosion damage we call this Vaporous Cavitation. There are a number of ‘good’ particles within Hydraulic oil which help with things like anti-wear, anti-foaming and oxidation agents , we need to be careful not to over clean the oil with very fine filtration and take the good agents from the oil.
If you have any more questions on the ISO Code or Filtration, please speak to our technical team on 01452 523352.
Not only can fluid condition monitoring be used on hydraulic oil but it can also be applied to engine oil. Service plans can be devised to match the condition of the machine, which can predict faults before they occur and can extend the life of both hydraulic system and engines.
For example, the Port of Tacoma in Washington has been testing hydraulic fluid since 1994. They originally had costs of $45.52 per hour just for maintenance but since initiating their fluid cleanliness program, they were able to cut costs by as much 97%.
The 75-gallon reservoirs on their straddle carriers and lift trucks were the first to undergo the testing. With tyres that are 6ft in diameter, you can imagine how large these machines are. They use ISO 46 hydraulic fluid from Chevron.
Their approach went like this:
The contaminants and their size were first worked on through particle counting. Using the two measures provided by the ISO 4406 framework – the count of how many particles were 5-µm and greater in size and how many were 15-µm and greater. This system delivers two numbers ie 17/15 which provides a range of the number of the particles.
Setting a target cleanliness level, the port authority decided that measurements of 14/11 and 15/13 were suitable for their straddle carriers and lift trucks. The first test produced fairly high results, so the port authority realised that they could extend the life span of their machines by a considerable amount, based purely on reducing the particulate contamination.
A filtration system was installed that was highly effective at capturing particles. This is something that made a huge difference to maintenance costs.
The port authority then focused their attention on engines and also set cleanliness targets along with new filtration systems. This resulted in an extended oil change interval in addition to an extension to eh engine overhaul periods.
Overall the investment paid off and they cut their maintenance costs by a dramatic figure in addition to cutting downtime.
In this economic climate, it’s important for everybody to focus on optimising productivity, decreasing maintenance and service costs for hydraulic equipment. It’s for these reasons that it’s vital that technicians pay attention to contamination control.
Effectual contamination control is not something that is always easy to handle. It’s something that needs you to set targets and demand the results that you want. This is why it doesn’t hurt to include consideration of any fluid into your hydraulic equipment system. To give a better understanding of what’s necessary, read this case study of what happened on a sugar cane farm in the USA.
With 15 cane harvesters in operation, it was becoming increasingly expensive to maintain the harvesters. There appeared to be a continual need to replace components that had failed. When technicians were called in to test the fluid, it was reading ISO 20/22 and this was proving to be very expensive. Every season each machine was needing a new pump at least three times.
The investigating technicians stated that the company would need to upgrade their filtration to expect better results. Work on this started by creating a prototype by modifying one of the machines. This proved to have potential, and two more machines were then modified.
Four years later, all the machines had been modified and there was only one pump going down at a rate of one time per 3 seasons.
With their data in hand, the sugar mill owners asked the manufacturer of the cane harvester whether they could make some modifications to their machinery before it left the factory.
In addition to improving the filtration, a few other points were improved upon such as modifications for pressure and temperature. Doing this also improved conditions resulting in the pump life being extended, but this result was mostly related to the filtration. For the owner of the hydraulic equipment, they could now see what a difference better filtration made in terms of running costs and machine reliability.
Set your own cleanliness levels
Take into consideration the following factors when attempting to set your own levels of cleanliness:
How sensitive are your components?
This measurement is known as contamination tolerance.
Another important factor is that of pressure. Remember that the greater the pressure, the more sensitive your components are going to be to contamination issues.
Finally, you’ll need to take into account the duty cycle severity, the fluid type, safety concerns and the machine criticality. All of these should be considered to create the levels of cleanliness that you’re looking for to ensure that your hydraulic equipment runs as it should without regularly component failure.
Although in our case study, they purchased a lot of pumps before establishing what they needed from a hydraulic system, they did get there in the end. The message from this article is that it’s essential to consider each of these factors prior to purchasing a hydraulic machine.
With the end game in mind, the reliability and maintenance outcomes have a high hope of being achieved, even before you have had any newly ordered hydraulic equipment delivered. Just as we saw in the case study, you can achieve the contamination control targets that you set just as long as you know what they are.
Your approach for this should be to start with the hydraulic oil that you’re most likely to use, take the weight and the viscosity index so that you can establish minimum viscosity for what the max running temperature of your machine will be. You can then inform the manufacturer what the maximum temperature should be in addition to what’s required in terms of cooling capacity using the typical temperature of your location as a guide You can then have a custom temperature system as opposed to a standard system.
Once you have done this, you can consider yourself as rather a seasoned hydraulic machine user. This will be particularly true if you specify that you want a flooded inlet for the hydraulic pumps, and no depth filters are installed on the motor case drain and piston pump lines.
If you don’t take it this far, then at the very least, you should define what you want from your hydraulic system in terms of cleanliness and operating temperatures. For the more reliable and dependable hydraulic system, you should ensure that these considerations form part of your selection process.
It’s no secret that contamination in hydraulic fluid systems can cause no end of issues. If you’ve been following our blog posts for a while, you’ll know that basically efficiency is increased by minimising gaps and clearance between moving parts. But whatever you do with this, particles can and will abrasively wear against components and can even lodge themselves in valves.
Contaminants can be easily introduced, for example with the addition of a component that is not fully clean. Manufacturers are aware of the trouble that contaminants can cause and they will try to improve matters for us mere mortal engineers. Here’s how manufacturers of hydraulic equipment minimise contamination:
As with any other engineering, identifying suitable contamination limits is about analysis costs/benefits. Although it’s obvious that a clean part is preferred to a dirty part, there is of course a cost associated with achieving that cleanliness. Therefore it’s important to the sensitivity of contamination and the working pressure of the system to establish the correct limits of contamination.
The measurement of contamination limits is specified in milligrams (mg) and length (longest chord) of the largest particle present.
Verify the Cleanliness Level
It’s possible to remove contamination from hydraulic components by rinsing them under pressure, using an ultrasonic cleaning device and giving functional bench-test methods. Using an extraction fluid such as a petroleum distillate is preferred as it does not encourage rust nor does it interfere with the filter membrane used to measure the level of contamination.
Recently an engineering organisation tested contamination levels of over 100 new hydraulic system components. Within their collection they looked at pumps, reservoirs, tubes, hoses, valves and other fittings. They found more than 8mg of dirt and debris on one of out of three of the components. All of this can be taken through the rest of the hydraulic system upon start-up of the machine.
Contamination is produced during any manufacturing or adjustment process. Even cutting a hose can create particles of rubber and metal. Performing the task of machining a valve manifold will create cutting chips. Welding spatter is produced from fabricating a steel reservoir and welding can also introduce iron-oxide. In every situation components should be prepared for use before adding to a fluid power system.
As new systems are put together, it makes sense to check what their contamination level is. This is a common activity for manufacturers to undertake as part of a testing procedure whilst systems are still being put together on the assembly line.
Using online portable particle counters is the preferred approach for verifying the level of cleanliness. These types of particle counters provide a rapid result and they don’t come with the issues that bottle sampling can.
Under certain circumstances, it’s possible to clean the system by cycling the actuators. If the fluid is not returned fully to the reservoir by the components, then it might be necessary to use an auxiliary flushing cart to attain the correct cleanliness level.
Once a system has been assembled, cleansed and then shipped, it needs to remain sealed in order to prevent any contamination from occurring. Keep in mind that engineers have observed that it can do more harm than good to perform oil changes during the first 2000 hours of machine operation. This is because new oils are not always clean and it’s often the case that end users don’t have the required equipment for filtering the fluid.
It’s vital to start the machine with a clean hydraulic system if you’re looking for a reliable and long equipment life. It’s the only way that you’ll be able to minimise it’s contamination from the outset and hopefully be able to continue to keep control over what’s going into your system and how much damage it does to components.
In today’s uncertain economy it’s critical to practice proactive hydraulic system maintenance to avoid untimely failure of components and the associated cost. If you suffer from a failure, then check whether your components are still under warranty from the supplier. If they aren’t, then your maintenance budget will have to bear the cost.
Avoid component failure
For this reason, our recommendation is to put focus on the following activities to lower the risk of component failure:
· Maintenance should be proactive as opposed to reactive
· Apply the rock solid principle of using the right oil and keeping your machine dry, cool and clean
· Design your hydraulic system to deliver the results you want in terms of reliability and maintenance goals
· Apply the use of checklists to ensure regular maintenance and to determine hidden failures
However, the reality of operation is that it’s still possible for failures to occur even when all these preventative fundamentals are applied. When a component fails the first query is usually about who will cover the cost? Normally it would be the party who has been negligent. But identifying who has been negligent and then getting everybody on the same page with it, is often far easier than it sounds.
Factory Produced or Refurbished?
If the component in question was installed pretty much straight from the factory floor, then questions will be asked whether it was installed correctly and about the conditions of its operation. These questions will include how clean the oil was, how hot it was and whether the oil had the correct viscosity. Was there any wrongdoing by the operator, faults with the circuit design or incorrect operating pressure? Although it’s possible that the manufacturing plant produced a defect, it’s not common and this will usually be ruled out.
However, if the component was refurbished or rebuilt, then the quality of this in addition to the above questions will be asked.
Whatever the source of the failed component is, it’s critical that a complete and detailed analysis takes place to identify the cause. In truth, analysis of component failure is a critical task that plays into proactive and preventative maintenance of any upkeep program.
The rationale behind this is that if the reason why a component has failed is not found and rectified, then the same fate could happen to a replacement part.
Handling analysis of the component failure requires specialist expertise. There needs to be a full understanding of hydraulic circuits in addition to a good understanding of the construction of the component and their methods of failure. This will usually be taken on by the manufacturer or the rebuilder of the component. This then leaves the machine owner’s perspective out of the equation, which can cause some frustration depending on what information you may have to add.
Having witnessed and been involved in a number of warranty claims – both here and at previous companies, we have learned the following:
1. The analysis of a failed component is not always clearly determined.
2. Although a rebuilder may recognise that he has made a mistake, he is not always willing to admit to it.
3. It’s not everybody who gets involved in a warranty claim that has the expertise and experience to do so.
4. Of course contamination and cavitation can have adverse effects on components, they cannot always be used as reasons why.
In some cases, it really does make you wonder whether avoidance of taking responsibility is a strategy to avoid warranty claims.
However, it’s important to understand what has compromised the longevity of a component. Is it operational issues, storage or erroneous installation?
Component suppliers worth their weight in gold are those that advise on potential pitfalls.
In summary, if there’s one thing that needs to be applied in this industry, it’s this: Wherever you are positioned in the component cycle, manufacturer, supplier or operator, it’s your duty to take reason steps to stay outside of the warranty claim process.
Our latest blog looks at our in-house Test Rig which is used to test many of our larger power units before they leave our premises for delivery to customers.
We are proud to be able to re-assure our customers that we fully test our units after they are built as to ensure our end users are satisfied with their product. This gives you, the customer, peace of mind that you have bought a reliable unit that, properly maintained, will last long into the future.
Below, we have covered the common test procedures for our Power units and how they are carried out:
This is carried out to remove debris and contamination from all valve, pipework and reservoir internals. Always ensuring that sufficient flow is generated by our test rig ensures a high velocity turbulent flow (above Reynolds number 2000). This action will agitate any debris that is lodged in corners and crevices.
Guaranteeing we supply the correct flow rate is crucial to ensuring the customers application runs at the speeds expected. So Hydraproducts is able to measure the hydraulic pump flow rates using the latest digital flow meter technology up to 150lpm.
Measuring pressures throughout a hydraulic system gives a hydraulic engineer a thorough knowledge of how it is performing and enables the setting of pumps and valves. Using a fully UKAS calibrated pressure test system, we are able to certify our systems with confidence that they will perform as expected.
Measuring the power input to a system is fundamental to confirming that the system has firstly been designed correctly and secondly that the combination of the pressure and flow are being achieved within parameters set by our hydraulic design engineers.
Many of the systems we manufacture are for lifting or clamping applications, where load holding for long periods is critical to the machine performance. Over the years Hydraproducts has developed a very stringent method of checking this that far surpasses those used by component suppliers. This enables us to check a whole system is holding pressures without decay.
This test focuses on the cleanliness of the hydraulic system as any contaminants from particles and foreign bodies entering the system can greatly affect its operating ability, causing wear and even failure in vital system components. The test adheres to strict international cleanliness standards and is carried out on a regular basis.
A vital system test which focuses on the system temperature in varying operating conditions and is carried out to make sure that temperatures are within standard set tolerances and do not exceed them when increased load is added.
The test ensures that system components do not suffer damage and wear from the increased heat levels given off by the system, which could render a system inoperable and could potentially result in large repair bills.
Filtration and Particulate Cleaning
Hydraulic filters work to ensure that particulate matter doesn’t find its way into the hydraulic system. It is essential that they are inspected and cleaned regularly to ensure excess particulate isn’t clogging the filter and affecting system performance.
Environmental conditions such as dusty workshops and foundries can affect the levels of contaminants entering the filter, and in these situations the filters will have to be checked more frequently and cleaned or replaced accordingly.
Contaminated hydraulic oil is the biggest cause of system failure in hydraulic machinery and often it is entirely avoidable. Mistakes happen, and there is always room for improvement in maintenance and routine replacement activities which can help reduce contaminants in the system. Even when you have got everything right in that area, there are still extra tweaks you can make or things to avoid when refining your hydraulic machinery care process.
Using the correct weight and ISO rated hydraulic oil is essential operating practise with any type of hydraulic equipment. Using liquid that is too thin or one designed specifically for a different type of motor, can cause serious damage to the internal parts through overheating or having an unsuitable level of intrinsic contamination. However, it is possible to go one step further than simply using a dedicated oil; By checking the ISO rating of the standard oil and the rating that the machinery requires, and then using one with lower ratings, i.e. with a higher level of cleanliness it is possible to improve the lifespan of components operating at a higher than average pressure, speed or length of operation. These factors affect the suitability of the standard hydraulic oil for any particular system and by taking into account any higher than average operational requirements, it is possible to avoid premature component failure caused by contamination levels in the fluid.
When looking at whether a different rated hydraulic fluid would be more suitable for your system and deciding to opt for a lower rated one, it is important that this decision is made with the most sensitive component in mind. It may be a case of using the hydraulic fluid with that rating, or of installing added filtration systems before that part of the system, in order to clean the fluid as it passes through that part. They say an army marches at the pace of the slowest person and it is similar concept to choosing hydraulic oil and filtration systems, when there are different levels of capability and tolerance between the component parts.
As a guide, the typical cleanliness required of hydraulic fluid for different types of components is as follows:
Servo control valves
Vane and piston pumps
Direction and pressure control valves
Gear pumps and motors
Flow control valves and cylinders
An avoidable source of contamination in hydraulic fluid is paint flakes or rust in the system. Sometimes a decision will be made to paint the inside of a hydraulic reservoir to prevent rusting, and on the surface. This may seem like a sensible decision as tanks are not cheap to replace and when a piece of machinery is expected to last a long time, it is reasonable to take precautions against such problems. Rust in hydraulic reservoirs can be caused by condensation and settled water in the space above the oil level, but a simpler solution is to keep the reservoir topped up and using a hygroscopic breather to reduce the potential for any water or vapour to form. Painting the tank with a rust proof paint may not cause any problems, but the potential is definitely there and the risk is not worth taking.
Monitoring the cleanliness of hydraulic oil at all stages of its journey round the system is important for maintenance and replacement of filters and elements, but also for the daily operation of the machinery. When it is possible to check that everything is operating as it should, then the focus can remain on the job at hand. Monitoring also alerts users to a potential problem, as if the contamination level of the hydraulic fluid is too high at a particular point, an alarm or warning light can be deployed and the machinery switched off while the hydraulic fluid or filter element is replaced. Being aware and alert to these issues and resolving them before they cause damage to the parts, is preferable to continuing blindly and then incurring hefty costs down the line.
The steps outlined above go a lot further than simple best practice – these are next-level preventative activities, that can save time and money for companies already acting in a contamination-aware manner. There are always small improvements that can be made to the operation of hydraulic machinery and it is hard to implement them all, but at least the knowledge expansion can inform suitable changes to your operating practices.
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