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Next time you cut a hose for your hydraulic system, there’s something that you need to know. Each time you use a blade on the wire reinforcement it’s going to create metal particles or some type of dust from the friction and cut on the outer or inner lining of the hose. This can introduce contamination in your circuit.
Fortunately, there are ways to do hose cutting that will reduce the risk of contamination such as using a wet blade as opposed to using a dry one. Either vacuuming or blowing air through the hose could also remove dust. Of course, when a long length of hose is cut, or when out in the field this might be difficult to do.
It’s important to do all that is possible to remove the cutting residue, or any other dust or contamination that could be in the hydraulic hose – before you install it. One of the most popular ways to do this with most hydraulic engineers is to blow through a foam cleaning projectile.
The manufacturers of this solution claim that it’s possible to achieve very clean hoses from using these products. As with anything else, it will depend upon a number of things as to whether this achieves this promised cleanliness. For example, it’s important to use a projectile that is of the same size as the hose being cleaned. In addition it will depend upon the number of shots used and whether you use a dry or solvent wetted projectile. If you’re planning on crimping the ends, ensure that the projectile is performed prior to that action.
These days we understand that most hydraulic hose fabricators have access to hose cleaning projectiles. However, it’s another matter with regards to how thorough they are with their cleaning. If you are looking for very clean hydraulic hose assemblies, it’s something that you must specify to the manufacture.
Recently one of our clients told us that he received a hydraulic hose from a manufacturer and he checked it by pouring solvent into it before he installed it, he was absolutely flabbergasted by the amount of dust and other rubbish that came out. Be sure to check your hydraulic hoses before installing them.
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.
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.
It’s no secret that hydraulic systems are sensitive to contamination from fluid or oil. Those that are kept clean and protected against the introduction of dirt or water, can run reliably. However, if any contamination is allowed to slip then there will be problems ahead.
Clearances are tight in hydraulic systems and the components such as cylinders, valves and pumps are markedly sensitive. Even a small foreign particle is likely to cause a problem.
Although the layout of hydraulic systems differs from system to system, there are of course the basic elements that are common across the board. For example, the hydraulic reservoir can become home to contaminants or there can be a filtration system employed to clean the fluid.
There is also the pump. Depending on whether a gear pump is in use or a vane or piston pipe that generally have tighter clearances is installed will depend on how much contamination your machine will withstand.
Finally, the flow control valves range in sensitivity, with servo-controlled systems being the most particular. The simpler setups that involve directional or check valves will handle more contamination before failing.
The smartest way to handle the risk and fallout from contamination is to develop a contamination control strategy. This should be built around:
· Control targets determined by your system design
· Detailed actions to ensure that your contamination control targets are met or exceeded
· Measurement by analysis of your oil to check if cleanliness targets are met
Let’s explore these further:
Cleanliness target development
Hydraulic systems suffer most from particular contamination and water contamination. However, heat and air can also have detrimental effects on them. Particles within the range of 1 to 10 microns ideally need to be captured. To put this into perspective, 3 microns is around the size of a human hair thickness, but this sized particle can bring down a hydraulic system fast. Clearances between moving parts in systems are typically made for between 1 and 5 microns to pass, but it’s not always going to be the case.
How to exclude particles and moisture
Once a target for cleanliness has been identified, then it’s important to take action to ensure that these goals can be achieved. The most important areas to look at now are the exclusion of contamination and its removal. Exclusion is focused on ensuring that contamination doesn’t get into the system and removal is built around the use of filters. Keep in mind that removing contaminations can be very expensive, so a strong focus should be put onto exclusion.
Looking at how to exclude particles and contamination involves checking every step of the lubrication oil process. This includes when you receive the oil, how it’s handled, stored, dispensed and its use in the system. It’s a surprising but disappointing fact that many oils that come into a plant can actually be too dirty to use without initially going through a filtration process. Some engineers recommend that new hydraulic oil should go through a filtering process at least 5 times before they are used.
Now that you have your exclusion system and other contamination control systems in place, it’s important to measure how effective your process is. Use the ISO 4406:99 system to check to what degree your hydraulic fluid is contaminated with particles. Take samples from the machine, preferably from the actuator return lines. You may also take them from the reservoir, but taking them from there will not provide you with information as to what’s going on in the rest of the system.
In summary, the reliability of any hydraulic system is dependent upon its levels of contamination. By keeping it clean you can decrease problems. Once any hydraulic system is contaminated it will lead to trouble and expense. It’s possible to control contamination in the most challenging of environments by using this simple three step process.
As we sympathise regularly with our readers, running hydraulic systems can be very costly. Not only can costs build rapidly from replacing damaged or worn components, but there is also system downtime to consider and to add to the expense.
If there is one deadly enemy for hydraulics, it’s contamination. In fact, contaminated fluids can be connected to more than 80% of all hydraulic failures. This includes all the related failures that can result including those of hoses, fittings, pumps and valves.
In fact, there is such a strong correlation between contamination of fluid and the lifespan of components that manufacturers of hydraulic and filtration products actually publish charts with the consequence predictions of not having inadequate filtration installed. Those systems that undergo rises in pressure will suffer from even more damage as contaminant particles make their way around the system.
Unfortunately the particles involved in hydraulic system contamination are usually far too small for the naked eye to see them. This is why it’s essential to use instruments specifically designed for contamination monitoring, otherwise a high system reliability cannot be expected to be maintained.
Although the operators and engineers who take care of industrial hydraulic systems are well aware of this problem, it’s only really coming to the fore of the mobile hydraulic system now. In this microcosm of the hydraulic world, there is still some time-based fluid maintenance going on. However, it’s becoming more apparent that this and spin-on filters are no longer enough to keep mobile hydraulic systems operating at their peak performance levels.
Quantifying contamination in hydraulic systems
Ideally every hydraulic system should have absolute filtration to capture both micro particles and those that are larger.
A Beta ratio of filtration will usually capture 99.5% of all particles that could contaminate a system. Alternatively the 1000 measurement will capture 99.9% of the particles. This will support the hydraulic system in enjoying a maximum service life. However, in addition to the Beta ratio, there are other considerations to ponder over when looking to keep the system clean.
How much dirt a filter can hold and how stable Beta ratio is will determine how well the filtration works out for the system. The best filters are usually cartridge-type that use a number of layers to help to maximise performance for all areas. Each layer will help the filter to either capture the dirt, hold it or to deliver the beta stability.
Another unexpected benefit of the cartridge-type filters is their ability to reduce how much loss of fluid there is when the filter is changed. This can keep go towards keeping costs down, whilst also lowering the impact on the environment. Although the cartridge type filter may cost more to buy, they deliver when it comes to protecting the system and cutting back on fluid loss.
With industrial hydraulic applications, cartridge filters are now considered to be the standard. They are also becoming more popular and widespread in the mobile market, which is becoming more sophisticated when it comes to components in addition to enduring rising costs.
Mobile Filtration Challenges and Solutions
Another area of concern with mobile hydraulic systems is that of space in the system to add filters and other components such as sampling valves. Quite often manufacturers will produce tank-top filters that can be integrated into the hydraulic reservoir, but sit out of the way. With global emission requirements becoming tighter, this trend is likely to accelerate in the coming years.
One issue that is unique to the mobile world is that of the cold start. It’s well known that any hydraulic fluid will thicken when sat at lower temperatures. This can increase the pressure drop for the filter element. The performance will take a downturn until the fluid begins to gain temperature and reaches the operating temperature level. Quite often the comment from an engineer will be ‘I started up and when I hit the level, nothing happened’.
Although it’s possible to install a large filter, it can add to the bulk and the cost of the system. Another work around is bypass the filter by adding in a pressure relief valve until the fluid is warmer. However, this can send contamination downstream. An approach that is less troublesome is to return the fluid to the reservoir as opposed to allowing it to circulate throughout the system.
In summary, as an engineer, the best move you can make is to identify and implement a fine filtration strategy that will enable your hydraulic system to run at its ultimate performance.
With hydraulic fluid contamination being the cause of more than 75% of hydraulic system failures, it’s important to know how to reduce it.
Hydraulic fluid contamination can cause many negative effects. For example, it can degrade fluid and prematurely age it. It can also raise the rate of internal leakage which will impact on performance and also decrease the efficiency of components such as motors, cylinders and pumps. Valves that have been affected by contamination will have a greater challenge when it comes to controlling pressure and flow, which will lead to increased heat being generated and wasted horsepower.
That’s not all of the issues hydraulic fluid contamination causes though. It can also make components stick or even seize when there are large amounts of contaminants getting stuck in clearances. This sludge and silting can be very damaging to hydraulic systems.
So where is all this contamination coming from?
A number of sources are involved including system wear, the manufacturing process, exposure to environmental contaminators, servicing and even hydraulic fluids themselves.
Read on to find out ways that hydraulic fluid contamination can be reduced.
Contaminants of hydraulic systems aren’t always solid particles, they sometimes come in the form of liquids, with the most common one being water. Solid particles can cause a lot of damage either by affecting the flow of the system by accumulation or even by reacting with the fluid.
Unfortunately, many new hydraulic fluids can contain high numbers of solid particles that are more than 5 µm in size. This will exceed recommendations coming out of most hydraulic system manufacturers and can be very harmful – especially when you can find over 500,000 particles in just 100 ml of fluid. Standards for cleanliness of hydraulic fluid are plentiful. This actually makes this issue worse.
When it comes to water, contamination can have a number of different effects depending on which system it’s in. It might be that water forms an emulsion or it may be slightly un-mixable (immiscible) and then float on the surface or even sit on the bottom of the fluid. Water can go on to create a lot of corrosion including that done through the process of cavitation. How water gets into the system is puzzling, but most often occurs through flaws in the design, servicing and maintenance or even through internal generation.
Contaminants can enter the system if there is improper storage of fluid in containers or inadequate fluid transfer. They may also enter when components are replaced and through the reservoir breather.
With moisture being so harmful to hydraulic systems, it’s essential to keep hydraulic fluid in proper storage. Even waterproof containers can allow moisture to enter when they are kept in a wide range of temperatures through condensation. By storing containers on their sides, it’s possible to prevent water from accumulating on the tops. In addition, it’s critical to check the lids of containers every so often to ensure that they are tight.
Additives in the hydraulic fluid can also cause degradation of it. For example, there are some additives that contain contaminants that are soluble in the additive, but not in the resulting hydraulic fluid. For example, corrosion inhibitors can create a slime as soon as they come across moisture. Others can create corrosion of steel.
If you opt to flush out the system, unless it’s thoroughly cleaned, you can have contaminated liquids. Although you may know of two fluids that are compatible in theory, as they do not develop a slime or other insoluble material, they will still be contaminated when mixed as they may not retain their individual performance properties.
In summary, the best way to reduce hydraulic fluid contamination is to use good handling and storage processes. Maintenance and flushing will need to be undertaken with care when cleaning out the system properly or by draining out the old fluid, and adding new fluid a handful of times to ensure a 95/5% mix.
Hydraulic filtration is a vital component of keeping a system running smoothly.
For example, did you know that up to 75% of failures with fluid power can be attributed to contamination? With the use of hydraulic filters, contamination damage can be significantly lowered which can not only cut down on expense but lower that 75% drastically.
If you’re looking to save costs from less downtime then it’s also time you looked into what a difference hydraulics filtration can make for extending the life of your equipment. Running your system optimally is essential when it comes to cost saving, but protecting its longevity is also a critical element in running any business efficiently.
Muck and dust can destroy a hydraulic system, that’s why it’s essential to make the best use of hydraulic filters. You wouldn’t even be able to remove that dirt yourself, as it’s likely to be dust that is so fine that you won’t be able to see it without the use of a microscope. Dirt has the same detrimental effect as sandpaper or gravel and not only will generally deteriorate the system, but it could even destroy it.
However, through the use of a hydraulic filter system you will be able to maintain control over the level of contamination and by doing so reduce the failure of systems by as much as 75% just be removing that dirt.
Hydraulic parts are expensive. Combine that with down time and having to keep engineers on hand to fix worn components and that’s a lot of expense to deal with. Putting filters into place can even save costs by increasing how long the hydraulic fluid will last.
Degradation of fluid – hydraulic fluid that contains fine metallic particles can degrade rapidly through chemical breakdown. Without protecting against this, there could be issues such as slippage, internal leakage, corrosion or sticking parts.
Scoring of surfaces – this can occur when particles get trapped between surfaces of seals
There’s no doubt about it, but …
· System performance is affected by dirt levels
· Hydraulic filters can control levels of dirt. Without using this management method, the system will get dirtier and dirtier until it fails.
In fact, hydraulic filters are the only way to control how much dirt is in fluid. Without them you will be forced to change out the hydraulic fluid regularly, which can be a time consuming and costly event.
Hydraulic system dirt particles are incredibly small. In fact, they are so small that they cannot be seen by the human eye – and 98% of hydraulic fluid has some dirt in it.
Engineers have found that when it comes to size of particles in samples taken from operating systems, the smaller the particles, the more dirt there is in the system.
So where do these particles come from that we have to work so hard to deal with?
In order to have an idea of what goes on inside the closed system, let’s examine where these particles come from.
Instead of enjoying the typical 20 gpm that is the measurement of a pumped flow from a 2000 psi system, you can expect to see something in the region of just 10 gpm. Although your pump will still produce for you, you’ll discover that the degradation results in just 50% efficiency and you should als be prepared to experience extra heat and other unwanted issues.
As with any hydraulic system, there is an optimum level of cleanliness, but there is a point where you cannot get any better performance out of the system by improving the quality of the fluid. However, with the use of hydraulic filters you should be well set to extend the life of your machinery.
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