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Preserving the quality of hydraulic fluid is something that will make a huge difference to the life span, lack of downtime and condition of your Hydraulic Systems and Machines. If it’s condition is allowed to degrade, you’ll be setting yourself up to have to deal with cavitation, machine damage and eventually the machine could even come to a halt. This is not going to look good in front of your boss nor your next employer.
That being the case, let’s explore what you need to know in order to preserve the quality of hydraulic fluid in your system.
After you’ve completed reading this post, you should understand what hydraulic fluid should be like, whether it needs any additives put into the fluid and how to get maximum life from your fluid.
As we have covered, without your hydraulic fluid being in good condition, there is likely to be a negative effect on the running of your hydraulic machine. We always recommend to our customers that they continue to use the fluid that the manufacturer of their machine has suggested. It’s also wise to use filters in order to prevent the fluid from deterioration through contamination. The pump and reservoir unit should also be considered as these play a critical role in the health of your fluid.
These are the properties that you want your hydraulic fluid to have in order for it to operate at it’s best.
Compressibility – it’s not very easy to squeeze liquids into a lesser volume. This is why precise motion control is one of the strong points of hydraulics. If air enters the system, then it takes it into being compressible and it won’t work as it should. You can test how compressible fluid is by forcing fluid into a rigid vessel with a screwed plunger and measuring the pressure.
Viscosity – this is a measurement of how easily the fluid will flow. Low viscosity fluid (for example water) will flow very easily, whereas high viscosity fluids will flow slowly and with some difficulty. This is what will result in loss of pressure. However, it’s only fluids with high viscosity that will lubricate well, so a balance needs to be sought.
Viscosity index – as a fluid gets hotter, its viscosity will usually decrease. This means that as it heats up it can become less effective at lubricating. Less change can be expected from a fluid with a low viscosity index. It might be possible to improve on this with the addition of chemical additives.
Air absorption – when liquids are under pressure they will absorb gas and then when the pressure is released, they will release it again. This can be seen with fizzy drinks. Air will not be absorbed easily by a good hydraulic fluid without causing foam and froth. It’s possible to add chemicals in order to improve this. Chemicals can be added to prevent foam from building up on the surface of the reservoir.
Oxidation – this can occur when oxygen is in the fluid and combining with elements. It can cause the oil to thicken to produce a varnish. This will stain the surface of the components and will reduce the life of the oil. Although there are additives that can help with this, it’s important to keep out air as much as possible. The main reason for air and fluid mixing is when there is foam and cascading in the reservoir.
Corrosion – corrosion of metals can be caused by hydraulic fluids. This can be helped by using materials that are compatible with it in addition to the addition of chemicals to the fluid.
Wear – when chemicals have been added which encourage the development of surface film where surfaces meet, such as in pumps and motors, it’s possible to slow down wear.
Pour point – this is the name given to the lowest temperature point at which the fluid will flow from a container when tipped up. If you’re working in cold climates, it’s possible to add chemicals to lower this temperature.
Flash point – the name given to the point when the vapour produced by a fluid will ignite when a naked flame makes contact with it. A Pensky Martins apparatus is used to measure this.
If you haven’t done so already, take time to become familiar with these technical engineering terms. They will prove useful for testing, explaining if you need advice from a third party and for keeping records of the condition of both the fluid and your hydraulic system.
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.
Firefighters use hydraulic equipment on a daily basis when they put out blazes and rescue people from burning buildings or crashed vehicles. The ladder on top of a fire engine is raised and lowered by a hydraulic piston, that is controlled by the ground crew, with another set of hydraulic hoses controlling the extension of each section of the ladder independently, allowing the correct length of ladder to be deployed for each situation. The ladder position is also controlled by a hydraulic motor, that turns the ladder left and right, making it easy to get the ladder in exactly the right place by using all three hydraulic components.
It is not just the firefighters ladder that uses hydraulic power, but the rescue and cutting tools, as well. Fire crews are often called upon to rescue people from crushed vehicles and getting them free is often a time sensitive operation, so the large forces exerted by hydraulic cutters, rams and spreading equipment are vital in terms of getting people free as quickly as possible. These tools operate at 720 bar, which is a large enough force to cut through steel rods and easily bend the structure of a car or lorry cab. Often referred to as the Jaws of Life, some hydraulic rescue equipment combines cutting and spreading capabilities into one tool, as both these functions are usually needed in rescue situations. Hydraulic jacks are carried on some fire trucks that are called to the scene of a heavy vehicle crash, as lifting a crashed train carriage or petrol tanker requires some serious force to be applied quickly, especially if there are people trapped underneath or inside the vehicle.
The choice of hydraulic fluid is very important in fire engines, as by nature they are used in situations where high temperatures are present. The fluid used in hydraulic rescue equipment is usually a phosphate-ester fluid, that does not conduct electrical charge and is fire resistant. It is vital that the hydraulic fluid used is fire resistant and capable of operating at high temperatures. Hydraulic fluid does heat up under pressure, so adding this factor to the issues of prolonged exposure to high heat at fire scenes means that there are limited choices of hydraulic fluids for fire engines. If oil based hydraulic fluids are used there is a high risk of fire if a line breaks or there is a leak, so for safety reasons any fluids used on a fire truck must be non-flammable.
Regular checks and maintenance of hydraulic fluid levels should be performed with any equipment that uses hydraulic fluids, but in the case of fire trucks it can make the difference between life and death. Fluid reservoir levels should be checked under the same conditions each time, which is best done when the fluid is cold and the fire engine has not been recently used. Keeping the reservoir topped up reduces the risk of air entering the system through the pump, which can lead to faulty operation and lasting damage to the components. This is a job that firefighters can carry out at their station, but for testing the hydraulic fluid a professional service should be used. The hydraulic fluid should be replaced regularly to keep the equipment in good working order.
Each type of hydraulic equipment may use a different type of fluid, and it is important that these are not mixed up during routine maintenance. Most fire departments display the information clearly at the point of topping up on the inside of cap covers or nearby. It is also good practice to label the fluid containers so they are not accidentally used on the wrong engine or the wrong piece of equipment, as each fire department may favour a particular type of oil for each application, and when fire trucks are loaned out to other departments there is a serious risk of hydraulic fluid mix up.
Some companies run a lot of different hydraulic equipment. Firefighters are one example of a workplace that uses a range of hydraulic equipment, each with its own specification of the type of hydraulic fluid that is indicated for use. Construction, healthcare and agriculture also use a range of different hydraulically powered equipment, from hospital beds to hay balers and everything in between. Being in charge of maintaining all this equipment is a large undertaking, and a common theme for those tasked with keeping everything running is staying on top of the sheer number of different types of hydraulic fluids that are stored and used routinely.
There may be very good reasons why a piece of equipment uses a certain type of hydraulic fluid, but sometimes the choice is determined by the past – “we've always used that type of oil so we will continue to do so” – is a common reason behind why different types of oil are used. That, coupled with the fact that some engineers have their own favourite types, can mean that after a few years the stock of hydraulic fluids is running into tens of bottles, all half empty (or full, depending on how you look at things) and taking up valuable storage space. There are some ways you can reduce the number of containers and types of oil you use.
Firstly, identify which bottle correlates to which piece of equipment. There may be more than one for very complex equipment. Mark the bottles so you know what hydraulic fluid goes with what. Anything that is unmarked can be discarded, as it is probably not in use anymore. Any bottles that are old or have been open for a long time may have degraded past the point at which they are still useable – the more contact there is between a hydraulic fluid and the air the more degradation will have occurred, so to avoid accidentally using hydraulic fluids that have gone off it is a good idea to regularly discard old containers.
The next stage is to identify where the same, or very similar fluids are being used on more than one type of hydraulic equipment. All hydraulic fluids have a viscosity rating, but these are a guideline of the viscosity under normal operating conditions. There is a 10 per cent variation on the viscosity grade, so where there are fluids of, say, 38, 40 and 42 grade then one grade should fulfil the requirements of the three varying grades. Consolidating the same types of fluid into one viscosity grade for all pieces of hydraulic equipment could reduce the number of bottles considerably, and make it much easier for anyone replacing or topping up the fluid levels.
It is important when consolidating fluid choices in this way that one refers to the specification of each piece of machinery, to ensure that there are no special reasons why a particular grade of hydraulic fluid is used. Pieces of machinery that experience a lot of fluctuation in operating temperature may require a certain type of hydraulic oil to ensure premium performance throughout operation.
When choosing new hydraulic equipment, it is worth considering whether the fluid types indicated by the manufacturer matches what you already have, and whether you are able to use one of the hydraulic fluids you already own if they are a close enough match. By keeping things very simple and reducing the number of hydraulic fluids kept on site you can save money, time and avoid unnecessary cross contamination of fluids within the machinery.
During the development of modern hydraulics water was the fluid used most often. Freely available and cheap to acquire, water was the obvious choice. However, as technology moved on mineral oil became the fluid of choice; from the 1920s mineral oils were chosen due to their lubricating nature and higher viscosity than water. Mineral oil also has a much higher boiling point than water, so could be used in applications where heat was an issue for hydraulic machinery using water. Mineral, natural and synthetic oils are still used today as the base for all hydraulic fluids on the market, and ingredients are added to create a range of hydraulic fluids suitable for many different purposes.
It is very important in mechanisms like brakes that the fluid is not hygroscopic, meaning that it will not absorb any water. Braking creates heat, caused by the friction between the callipers and discs. This heat can boil and vaporise any water in the brake fluid, leading to the presence of a vapour in the system that will cause brake failure as that vapour is compressed by the action of the mechanism. It is for this reason that brake fluids are mineral oil or silicone based, and no other type of hydraulic fluid should be used in brakes or other mechanisms where such failure could be catastrophic.
Safety is also a concern in industries where there is a high risk of fire. Hydraulic fluids can be very flammable, but water-glycol and polyol-ester based fluids have naturally fire-resistant properties, meaning they are excellent for use in hydraulic firefighting equipment and other places where high heat, oxygen and combustible materials are routinely used. There is a similar concern for safety in environmental applications, such as agriculture, fish farming and other marine based industries. The failure of a seal or even a small leak in a pipe will cause hydraulic fluid to escape from the system and enter the environment, so it is imperative that biodegradable and non-toxic fluids are used in case of a spillage or leak, as these will not harm the surrounding habitats.
Hydraulic fluids are chosen for the properties that are needed in a specific application. In the examples above fire resistance, biodegradability and hygroscopic properties are very important, but there are several other factors to consider when choosing between fluids. Viscosity and lubricating properties are important in applications where it is not easy to change the fluid regularly (for example sub-aquatic machinery) as the hydraulic fluid also needs to help maintain the mechanisms. Lubricating fluids also have a low tolerance for water ingress so are good for systems where stopping action is just as important as the movement itself.
Aircraft controls use hydraulics to make the transfer of power from the pilots hands to the machinery easier for the pilot; many systems require a large amount of force to operate and this is unsustainable, especially on long flights or in the military. Hydraulic actuators initiate the systems, which are in turn controlled by valves operated by the pilot, flight crew or autopilot. The hydraulic power is generated by the engines and by a backup system that can be deployed in the event of engine failure or during ground maintenance, meaning that even in the event of main engine failure the control systems can still be operated. Aircraft hydraulic fluid must be handled very carefully to avoid contamination, as even a small amount of water or dirt in it could cause catastrophic failure of the systems while the aircraft is in flight. The fluids are checked during every routine maintenance check to ensure they are free from contamination. The types of fluid that can be used on any given aircraft are specified by the manufacturer, and should not be substituted for any other type.
As a multi-functioning and essential component to any hydraulic system, hydraulic fluid is responsible for lubricating components such as transmissions, and also gets involved in heat transfer and wear related conveyance.
This makes choosing the correct fluid for a hydraulic system a critical decision as it could make the difference between a finely tuned system and a costly failure. A number of factors should be taken into account when choosing the right fluid for your system; these include fluid viscosity, dependent on the temperatures the system will be running at as well as taking other operating parameters into account, system requirements and environmental conditions and regulations.
Key points to take into account when selecting fluids:
Fluid viscosity explained
Fluid viscosity can vary from application to application with environmental and climate factors playing a large part in this.
The lower the fluid viscosity, the thinner the fluid thickness. If this level drops too much there is the chance of metal on metal contact between componentry which is never a good sign.
Low viscosity fluid can also reduce the volumetric efficiency of hydraulic pumps and other components as it increases the chances of leakage occurring.
Effects of using the wrong hydraulic fluid
If a mistake is made and the wrong type of fluid is added to the system it is good to know the typical warning signs to look out for. For example, an oil with any variation of a set parameter can cause to damage to areas such as rubber seals, gaskets etc.
Just one of these damaged areas could put the system into shutdown and cause irreversible component damage, so it is vital that the correct oil specifications are used.
Selecting the correct fluid
After you have read up on your systems specs and the level of lubrication it requires, you can look at fluids that have the following properties which help protect system components:
· Corrosion and rust inhibition – most hydraulic fluids on sale today have anti-corrosion qualities added and these come in the form of a thin layer of film which settles on metal surfaces, protecting them.
· Hydrolytic stability – This is basically the chemical degradation of fluid over time due to the effects of water. This is mainly due to the additives in the fluid which react with the water. Zinc-based additives are especially bad for this and any components made from copper can react especially badly.
· Materials compatibility – Because of the large amount of components in a hydraulic system, most of which are made from different materials such as hoses, gaskets and seals; it is imperative that the fluid used has no adverse reactions to these materials and thus ensures system reliability and performance.
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