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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.
Cavitation was first discovered in 1917 when Lord Rayleigh (a British physicist) decided to investigate why fast-rotating ship propellers were eroding at such an incredibly rapid pace. He discovered that it was all down to a condition that came to be known as cavitation.
Cavitation is related to the word, cavity and has the Latin verb ‘cavitere’ at its root. It means to ‘hollow out’ and that’s exactly what cavitation does. Cavitation occurs when very hot small air and gas bubbles develop. As they reach high pressure areas they collapse and cause hot jets to hit the surface of any pipe or components that is reachable causing erosion.
When liquid passes through an hydraulic valve, it is under pressure due to the size of the valve. The speed of the flow will rise and then the speed drops again. This change in pressure will create a vapour and then small bubbles of gas will form. When the pressure gets higher than that of the vapour, the bubbles will collapse as the vapour liquefies again. The bubble collapse can send out the heated fluid jets which are very powerful and it’s this that causes so much damage to metal.
Cavitation is no joke. It can be so severe that it can completely destroy hydraulic valves, pumps and piping to such a degree that the entire system can fail. In between, you may need to contend with leaking valves or even holes in pressure vessel walls.
Even cavitation that is at a low level can wreak havoc by eroding components until they need to be replaced. This is how engineers can recognise that their system is suffering from the effects of cavitation:
· Banging or knocking noise
· Chocked flow
· Fluid property changes
· Valve component erosion
· Control valve destruction
· Failure of plant leading to shutdown
Cavitation damage can often be identified visually with the use of either a microscope or a magnifying glass. If you are wary that cavitation is causing damage to your hydraulic system, check whether or not it is general wear and tear through corrosion. Some types of corrosion will actually mimic what you’d experience through cavitation. You can expect to find cavitation damage, if it’s in existence, downstream of the seating areas for the control valve. You could very occasionally witness cavitation bubbles further downstream from there.
Another easier way to identify whether your system is suffering from cavitation damage is to listen out for the noise of either crackling or popping. As pressure drop occurs, the cavitation will ramp up and you’ll hear rattling or hissing that increases in volume. If the cavitation is in full operation, it will sound more like you have a lot of small rocks or gravel passing through your system.
Cavitation is so powerful that there is currently no known material that can stay undamaged by it. The only way to deal with it is to eliminate it.
One of the simplest ways to eliminate cavitation is to reduce the operating temperature within the hydraulic system. The vapour pressure will be eliminated. If you have identified a valve that is experiencing cavitation, when you replace it, try to install it at the lowest possible elevation within your pipe system.
Another possible solution to cavitation issues is to introduce air or nitrogen into the area of the system where you are expecting to get it. It will need to be added through either the valve shaft or through a tap downstream on aside of the pipe as close as possible to the valve.
If for some reason you are unable to change the process conditions, then it’s recommended that you use valves with low recovery and treacherous flow path as opposed to high recovery valves such as the gate, ball or butterfly types.
In this article we want to explain the ins and outs of hydraulic powerpacks. A vital piece of equipment that is used with so many machines we see every day.
In a nutshell, hydraulic powerpacks are self contained units that are used instead of a built in power supply for hydraulic machinery. Hydraulic power uses fluid to transmit power from one location to another in order to run a machine. It really is as simple as that.
So what do they look like?
In order to recognise and better understand hydraulic powerpacks, it is a good idea to get to know the key components. Hydraulic powerpacks come in many different shapes and sizes, some are very large and stationary whereas others are much smaller and more compact. In fact, some hydraulic powerpacks are so compact that they can easily be transported in a small van or even an estate car.
The only real way to identify hydraulic powerpacks is through its main components. No matter the size of the unit, all power packs will have the following; a hydraulic reservoir, regulators, a pump, motor, pressure supply lines and relief lines.
What do these components do?
It may be obvious to some but in this post we wanted to explain every component as simply as possible. So here goes.
First up is the hydraulic reservoir which quite simply holds the fluid. Reservoirs will come in different sizes.
Then we have the regulators. Regulators are vital as they control and maintain the amount of pressure that the hydraulic powerpack delivers.
Thirdly we have the pressure supply lines and relief lines. The supply line simply supplies fluid under pressure to the pump and the relief lines relieve pressure between the pump and the valves. The relief lines also control the direction of flow through the system.
Finally we have the pump and a motor. We will begin with the simpler component of the two, the motor. The motor is simply there to power the pump. Easy as that. Now the pump generally performs two actions. Firstly, it operates as a vacuum at the pump inlet and through atmospheric pressure forces fluid from the reservoir into the inlet line and then to the pump. It then delivers the fluid to the pump outlet and pumps it into the hydraulic system. We did warn you that the second part would be slightly more confusing.
So what is the function of hydraulic powerpacks?
Hydraulic powerpacks deliver power through a control valve which in turn runs the machine it is connected to. Hydraulic powerpacks come with a variety of valve connections. This means that you can power a variety of machines by using the appropriate valves.
Hydraulic powerpacks are relied upon by a range of different machines that use hydraulic power to do its work. If a machine is required to carry out heavy or systematic lifting then its likely it would need help from a hydraulic powerpack.
To make it easier for you to understand, we have included a list of trades that regularly rely on our powerpacks. On a building site you will see machines like bulldozers and excavators, which both need hydraulic powerpacks. But, it is not just on building sites that you will find these types of machines. Fishermen and mechanics both need hydraulic powerpacks too. If we did not have them then how would fishermen lift their nets or how would mechanics lift our cars?
When picking a hydraulic powerpack there are a variety of pumps and options to pick from and it is important to pick the right pack to meet your machines needs. It is also important to consider a pack that will help maximise productivity and minimise cost.
Many people will overlook the necessity of hydraulic powerpacks, but they really are vital to ensuring our society runs efficiently.
Do you need to maintain hydraulic powerpacks?
Yes you do and this is hugely important! Hydraulic powerpacks require regular maintenance to ensure they are working properly and safely and to help extend their life. Maintaining hydraulic powerpacks is relatively simple and includes checking the tubing, this can be for any noticeable problems such as dents or cracks. It is also vital to regularly change the hydraulic fluid and look at the reservoir to check for any corrosion or rust.
What hydraulic powerpacks do we provide?
Generally we provide four different types of hydraulic powerpacks. You can pick from a standard powerpack, a mini powerpack, a micro powerpack or a bespoke powerpack.
The standard hydraulic powerpack uses a standard range of modular components and is ideal for the most demanding industrial applications. The mini powerpack is ideal for applications requiring up to 5.5kW. The micro hydraulic powerpacks were originally produced for mobility applications, so are great for when space is limited. Finally, if none of these seem to fit your needs then we offer bespoke hydraulic powerpacks ensuring your application gets the hydraulic powerpack it requires.
Finally, who is the genius behind hydraulic powerpacks?
The man behind hydraulics was Laissez Pascal. A French mathematician, physicist and religious philosopher who lived in the mid seventeenth century. Pascal made observations about fluid and pressure which led to Pascal’s law. Pascal's law states that when there is an increase in pressure at any point in a confined fluid, there is an equal increase at every other point in the container. Hydraulic powerpacks have been designed based on Pascal's law of physics, drawing their power from ratios of area and pressure.
So, interested in our Power Packs? Come on over to the main website and see what we can do for your Hydraulic Power Pack Needs .
Although aeration and cavitation are very similar, they are caused by completely different situations.
Cavitation occurs when air cavities are formed and are then collapsed in liquid. For example, when hydraulic fluid is being pumped from the reservoir, the suction line to the pump will drop pressure. The fluid then gets pushed into the pump, rather than sucked. Aeration is caused when there is a leak on a fitting. Fittings can become loose from years of vibration.
Most hydraulic oil contains around 9% of air that has been dissolved. When the oil is not flowing fast enough to the pump, air will be pulled out of the oil. The air then goes into the pump at a considerably high pressure, and then implodes. This can cause the pump to whine with a high pitched sound as damage is made.
It’s also possible for cavitation to occur when there are extreme temperatures. For example, bubbles can form when the fluid is at a high temperature but at low pressure. Again, bubbles that enter the pump can collapse and create cavitation. It’s also possible for low temperatures to make the oil more viscose, and this can prevent it from flowing into the pump. (Oils that have a high viscosity index will usually resist this tendency, but they can be expensive, and are therefore not widely used). A best practice is to not start a hydraulic system with oil that is colder than 40°F. Not until the oil has reached at least 70°F should the system be put under load.
If the right amount of fluid cannot be delivered to the pump due to the drive speed being too high, then that can also create cavitation. The pump should not be mounted above the hydraulic fluid level in the reservoir otherwise there will not be enough atmospheric pressure for the oil to be delivered to the pump inlet. This is something that is a tendency of systems that operate high above sea level, due to there being lower atmospheric level conditions.
Read our hydraulic system blog regularly for more information about how to avoid cavitation and aeration.
To the hydraulic system maintenance engineer, it can be both normal and alarming that hydraulic oil contains air.
Nonetheless, it’s part of hydraulic fluid’s natural composition to contain between 6% - 12% of dissolved air. The trouble starts if this air transforms into being a form that is not dissolved, and it can lead to serious trouble!
If the air makes its way into the pump intake, then air can then transform into entrained air. The problem with this is that it can spoil the stiffness of the fluid, which will decrease its efficiency. It can also increase the levels of noise. But that’s not all.
Supposing the entrained oil reaches the pump outlet and gets compressed, you can then expect very high peak temperatures to develop. Air mixing with the oil film will oxidize it. The cracking noise is an indication of oxidisation. As we all know, it’s oxidisation that degrades hydraulic fluid. The air bubbles will then start to pop after smashing themselves against the valve plate of the pump and any other areas that they touch. This is when cavitation takes place and there’s erosive wear going on.
The only way to stop this occurring is to prevent it. Air will come out of the solution in certain conditions. For example, when the temperature of the hydraulic oil increases or there is a decrease in static pressure, then the solubility of the air is reduced and that’s when the fluid can host the formation of bubbles.
The release of the air is referred to as gaseous cavitation. It can come about from:
· Suction strainers or inlet filters becoming clogged
· The intake-line isolation valves causing turbulence
· An inlet that has been poorly designed such as it being too long, having multiple bends or the diameter of it being too small
· The intake line being restricted or collapsed
· There being too much lift between the minimum fluid level and the pump intake
· The reservoir being clogged or undersized
The bottom line is that although you will have air in your hydraulic fluid, it’s key to keep an eye on what condition it is in. it can be a serious and costly error to allow air to contaminate a hydraulic system.
Hydraulic pumps, one of the more common mechanical applications of hydraulic technology, use fluid to push an arm a set distance forwards and backwards (or up and down). One example is the mechanical arms of a digger or other ground-working machinery. A hydraulic pump is perfect for this use, as the machinery works using the set distances between the components of the arms.
A hydraulic gear motor uses fluid to power movement for a much longer distance (or to put it another way, for an unspecified length of time). The motor works by running fluid through a chamber containing two cogs. One is linked to the drive shaft and transfers the power to the component that needs to move, and the other is idle, existing only to complete the mechanism. The same fluid is pumped through the motor chamber for as long as the power is needed, and it works in a similar fashion to an electric motor, but is much smaller and can be used in places where electricity is not safe or viable to use. It is a natural development of the waterwheel that was commonplace in the UK during the Industrial Revolution, powering cotton mills, woodworking and even bellows for blacksmiths forges.
A hydraulic gear motor is more appropriate than a pump for any piece of machinery that needs continuous power in a simple mechanism; a series of hydraulic pumps, arms and cogs can be used to create continuous power, but the resulting apparatus is bulky and made up of several components, which increases the likelihood of mechanical failure. A hydraulic motor, by comparison, can be very small and portable, meaning it is ideal for any application that is a long distance from traditional power sources and remote areas of the planet where other forms of energy are not viable. They are also reasonably simple in construction, so parts and maintenance are not an issue.
Hydraulic motors are ideal for use underwater and in dangerous places like mines and gas works, where the spark from an electric or petrol motor poses a serious fire risk. They are also good for any task where the motor is operated remotely, as the fluid can be pumped a long distance to the motor using comparatively little power and the only connection needed is piping, compared to more expensive electrical cable for running a remote electric motor. What is the most ingenious application of a hydraulic motor you have ever seen? Let us know in the comments below.
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