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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.
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.
Electrostatic charge builds when there are two bodies moving and creating friction. The fact is that this also occurs in hydraulic systems from the friction caused by system components with moving fluid.
Although we haven’t had a lot of situations that have involved electrostatic discharge, it is still something that every engineer should be aware of.
When an electrostatic discharge occurs, there is a clicking noise as charge increases and is then released. This is something that will often occur in a filter – leaving burn marks and potentially other damage.
With the increasing preference of using non-metallic additives in hydraulic oils the electrostatic charge could be on the increase. Those hydraulic oils that contain anti-wear additives that are zinc-based have considerably high conductivity.
Conductivity in hydraulic oils helps when it comes to moving electrostatic charge around the system. Although zinc-based additives will rarely collect enough charge to cause a big problem, synthetic oils can. This is because they have less conductivity and therefore will potentially accumulate more charge before discharging it.
Another change that could lead to an increase in electrostatic discharge is that there has been a change made to the materials that filter elements are made of. In order to make them easier to dispose of them in an eco-friendly way, they have more non-metallic material in the design, which lowers conductivity and therefore increases the capacitance.
The manufacturers of hydraulic filters are aware of these issues, and are looking into how they can minimise or even eliminate these issues.
However, if you come across a situation where there is electrostatic discharge in the meantime, then consider this:
By adding larger filter elements you can reduce flow density and therefore the amount of charge that is being generated. You might also want to consider increasing the tank size so that the time between charge generations increases.
This is one of the reasons why you shouldn’t skimp on tank size or on filter capacity.
Hydraulics has been around for a very long time. But are you aware of how far it has actually come? You wouldn’t be alone if you responded with no. It is a very technical subject that can be quite difficult to understand, but in this article we want to tell you the story of hydraulics! We want to share with you who discovered hydraulics, what it was originally used for and how hydraulic power got to where it is today.
So why don’t we start at the beginning! Where does the word hydraulic come from?
The word hydraulic originates from the Greek word ‘Hydros’ which means water. Why water? Well, this is because water was the first liquid to be used in the hydraulic system. Today, hydraulics includes the physical behaviour of all liquids, not just water.
In the world of industrial, mobile and aerospace equipment, hydraulic power systems are very popular. They enjoy a high power-to-weight ratio in addition to being able to be stalled, operated intermittently and even reversed. They can also accelerate fast and are quick to respond. Another attractive feature of the fluid power system is that they can be very long lasting in addition to offer reliable operation rates.
Hydraulic systems are able to work as they contain incompressible liquid. In many situations, it’s much preferred to use hydraulics to move machinery. For one, fluid systems do not produce the same amount of wear as a dryer method would. It also does not require so many moving parts as a different type of system would.
The pressure of fluid in the hydraulic system is controlled by the valve. They also handle the flow rate and which way the flow is going. The funny thing about hydraulic valves is that they can change name depending on how they are being used and according to which system that are part of. Used in combination with cylinders and hydraulic pumps to control the flow of liquid, hydraulic valves are powerful.
The classification of hydraulic valves is determined by how much pressure they can handle. It is also related to the flow and how many directional control valves there are in them. They may also be classified on their looks and extra features such as needle valves, spools and poppets.
Apart from their ability at moving very heavy objects, one of the reasons that hydraulic systems are so popular is because they can operate at very low noise levels. In the manufacturing industry, a low noise level is sought after, in particular at less than 70dB. The hydraulic system and pump is able to accomplish this.
The hydraulic control valve is a clever piece of kit. Browse hydraulic valves here.
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