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Temperature is an important variable in many aspects of hydraulic motor operation. The operating temperature of the machinery informs the type of hydraulic oil used in the system, as it must be able to withstand certain temperatures without degrading or becoming too thin, both of which cause damage to internal components. The ambient temperature in which the machinery is located also informs this decision, as machinery that operates at low temperatures will require a certain type of oil, that remains at the right viscosity even when cold. Similarly, a high ambient temperature requires a hydraulic fluid that is capable of remaining thick enough even at these temperatures. Factoring in the increase in heat that comes from the operation of the motor should also inform the type of hydraulic fluid that is used.
Temperature shock in a hydraulic system is when the fluid in one part of the system has reached peak operating temperature and is then allowed to flow into an idle part of the system. In this idle part the components are cold, and expand when they come into contact with the hot fluid. The tiny spaces between moving parts are compromised and in some cases closed entirely due to the expansion of the metal and this causes seizing, erosion of the components and serious damage to the moving parts.
Temperature shock is a big issue for hydraulic systems which operate in stages, such as diving winches, where two motors are used to drive two winches, one which lowers equipment and another which brings it back to the surface. To start with the lowering motor is in operation, which raises the temperature of the oil inside the system. When the returning motor is initiated it is cold, but the fluid entering it has already been heated by the first motor. If you are finding that the same components in the second stage of the system are frequently wearing out or breaking and there is no other plausible reason for this, (such as incorrect maintenance, contaminated or incorrect fluid) then temperature shock is the most likely culprit. It causes expensive repairs and a huge amount of downtime that can be avoided with a simple measure.
The best solution to reducing and eliminating temperature shock is to continuously flush the motor case during operation. Only a small amount of hydraulic fluid needs to be flushed through the system, as it is not there for operation but to maintain a constant temperature. By keeping a constant temperature through all parts of the motor system, the components have time to adjust to the increase in temperature, rather than quickly expanding and seizing, causing breakages of vital components.
The flushing system does not have to drain any oil as part of this process, as the flushing itself is not intended to clear the system but to circulate fluid at a constant temperature throughout the system. A flushing valve installed between the pump, where most heat is generated and transferred to the fluid, and the motor case is a simple way of achieving the correct circulation. It is also possible, with some clever engineering, to adapt an existing case flushing and draining system to function as solely a case flushing system when needed, but this should be carried out by an experienced hydraulic engineer with experience of rebuilding systems.
If you're reading this then the operation of hydraulic motors is probably no secret to you, but perhaps the people you work with or machine operators struggle to grasp exactly what is happening inside the equipment, and more importantly, why? We have put together a short, user-friendly guide to hydraulic motors that can serve as an educational tool, for those not in the know and will hopefully reduce the number of repeat questions you have to answer.
In a nutshell, all hydraulic power systems comprise the same four basic elements. They are:
The size of these components can affect the speed, pressure, flow, strength and efficiency of the hydraulic motor but the basic concept is the same across the board. Essentially a hydraulic motor uses varying pressures conducted via hydraulic fluid to increase and magnify force in an energy-efficient and reliable manner.
The jargon terms used to describe hydraulic motor operation can seem confusing and complex to the lay person, but learning what these words mean and how they relate to the hydraulic equipment is important to fully understand what is happening during normal running, and also what is happening where there is a system failure.
Torque is probably the most important term which refers to hydraulic motors. It is used to describe the ability of the engine to translate pressure into motion and is measured in Newton Metres (Nm) or inch pounds (lbf). A hydraulic motor will have a starting torque and a running torque. The starting torque is the force required to start the motor turning and the running torque refers to the pressure generated to maintain operation, at a certain pace. Torque ripple refers to the difference between the minimum and maximum torque delivered during a single rotation of the motor.
Motor displacement is an important term to know. It refers to how much hydraulic fluid is needed to turn the motor through one revolution and is measured in centimetres or inches cubed per revolution. A motor may be a fixed or variable displacement type, meaning that either torque or speed is the priority. A fixed displacement motor has torque as the priority, running at a constant pressure. Speed can be controlled by varying the amount of fluid going into the motor. In a variable displacement motor both torque and speed can be controlled.
Hydraulic fluid replacement is also something that machine operators should be trained in, if they are expected to top up the reservoir or replace the fluid. Hydraulic oil comes in a variety of weights, which refers to the viscosity of the fluid. Different types of hydraulic fluid can withstand different temperature ranges and different chemical make-ups of hydraulic fluid are recommended for different applications. It is vital that the correct fluid is used, as any mistakes can cause costly damage to the equipment. When replacing or topping up hydraulic fluid, it is important that it is filtered before entering the system, (we have written more about this topic previously on this blog). Contaminated hydraulic fluid causes the same problems as using the incorrect product and it is crucial for operators to know how their actions can affect the operation of the machinery and cause problems.
Of course, there is a lot more to hydraulics than we have covered here, but the very basics that we have covered, should help hydraulic machinery operators understand a little more about their equipment, how it works, and most importantly, what can cause it not to work.
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 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 .
There are a wide range of choices over an even wider range of budgets, but the right hydraulic oil will prolong your machine life and reduce your overall running costs.
Three initial questions must be answered:-
1) In what type of equipment will the hydraulic fluid be used?
2) How severe will the duty be?
3) What operating temperature and pressures will be experienced?
4) Environment food safe etc
Answers to these questions will lead to the primary choices of viscosity grade (VG) and hydraulic fluid types.
In what type of equipment will the hydraulic oils be used?
Selection of a hydraulic fluid with a viscosity that bests suits the system pump is a good place to start. Manufacturers will normally specify a range of oil viscosity. These will vary dependent upon the pump type. Vane pumps typically require 14-160 cSt, Piston pumps are more durable than a vane pump and require 10-160cSt. Gear pumps are the most tolerant to contamination and a conservative range would be 10-300cSt. Industrial machinery is typically designed to operate within a cleaner more stable environment, where outdoor and mobile applications will more likely have severe temperature variations, higher humidity and more demanding duty cycles.
How severe will the duty be?
Duty would normally be described by running time, environmental factors, likelihood of contamination ingress, maintenance arrangements etc.
Examples of Low/Medium/Heavy Duty would be:-
> 24 hours
Heavier duty demands will normally lead to the use of a mineral oil with a good additive package (such as a HVLP) to improve performance or the selection of a fully synthetic oil.
For hydraulic systems with high running times a fluid with a high viscosity index (VI>130) will avoid damage and breakdowns as it extends lifetime of hydraulic pumps and components.
What operating temperature and pressures will be experienced?
Where temperature extremes are large (below -5oC and above +60oC) and pressures above 250 bar the use of a fluid with a good mix of additives will be important. Mineral based oils (HM/HLP) will be sufficient in the most common applications as these often have anti-wear additives, oxidisation inhibitors and viscosity improvers. Fully synthetic oils will however out-perform mineral hydraulic oil ensuring that the viscosity and lubricity remains stable over a longer period.
Viscosity Grade (VG)
A hydraulic fluid has a low viscosity when it is thin and a high viscosity grade when it is thick. The viscosity reduces as the temperature rises and visa-versa. The hydraulic fluid must be thin enough to flow through the filter, inlet and return pipes without too much resistance. On the other hand, the hydraulic fluid must not be too thin, in order to avoid wear due to lack of lubrication and to keep internal leakage within limits. Viscosity grade is expressed at 40oC eg ISO46 which is an oil with a viscosity of 46 cSt measured at 40oC.
According to DINISO 2909 oil viscosity changes versus temperature, Viscosity Index (VI), is normally between 90-110. VI above 130 are largely insensitive to temperature change.
A viscosity range of 12-80sCt is recommended for a large range of commercially used hydraulic equipment.
Hydraulic oil specifications
Hydraulic power packs can be used with a wide range of hydraulic oil grades, commonly:-
· Hydraulic Oil (ISO11158-HM) – Mineral based – hydraulic oil grades widely used in light duty applications where temperature and pressures are moderate.
· Hydraulic Oil (DIN51524-2-HLP) – Mineral based with additives for oxidation, corrosion and wear protection. Used for general applications where temperature and viscosity conditions are observed.
· Hydraulic Oil (51524-3-HVLP) – Premium grade mineral based as per HLP but with improved viscosity temperature behaviour (VI>140).
· Biodegradable hydraulic oil – HETG, HEPG, HEES and HEPR – A developing technology and is yet to replace mineral oils in all applications. Storage and service life is limited, particularly at elevated temperatures.
· Fire Resistant Fluids (ISO12922 – HFA, HFB, HFC and HFD) – HFA,HFB and HFC contain water solutions and must only be used with specifically designed products. Not suitable for systems containing aluminium and some paint products. Seal compatibility must be checked.
For Hydraproducts powerpacks we recommend the following:-
HPU and HPR Micro powerpacks
HPM Mini packs
HPS Standard Hydraulic power units
Some sources of these oils would be:-
HM32 – Shell Hydrau HM32 – Castrol Hyspin VG32
HLP32 – Shell Tellus 32 – Castol Hyspin AWS32
HVLP32 – Shell Tellus S3V 32 – Castrol Hyspin HVI 32
Where environmentally sensitive fluids are required the use of Castrol Carelube HES32 can be employed in all our products, for light and medium duty ONLY.
Where a small level of fire resistance desirable then the use of a Castrol Anvol SWX FM HFDU fluid may be implemented in all of our products, for light and medium duty ONLY.
Throughout the history of automotive development hydraulics have played a critical role in the engineering of brakes, steering and gears, as well as suspension. Specialist functions on road going vehicles as well as vehicles designed for non-road use, such as tractors, other agricultural machinery and military vehicles, also use hydraulic power to effect movement of harvesting machinery, aerial ladders and artillery. Hydraulic engineering offers a tested and trusted way of effecting actions with a quick response time and most importantly, it is reliable, efficient, and easier to fix than electrical systems designed to do the same.
Electrical systems are becoming more commonplace in road going vehicles, as the move to all electric or hybrid powered cars starts to take off in the mainstream. Electric actuators are starting to replace their hydraulic equivalent in some systems, especially those from manufacturers who are pro-actively making advances in alternative car design; self-driving cars and fully electric vehicles are pushing electric actuators to the fore of the minds of automotive designers. The appeal to designers is the easy integration of electrical components into an existing electrical system; if most of the controls are electric rather than mechanical it makes sense to extend the same technology as far as possible. Electric actuators are cheaper, easier to control and generally last as well as hydraulic actuators, and it is far easier to work these into the wiring and software system of a vehicle than to install a separate hydraulic system just to run the brakes, or the gearbox.
Advanced braking systems are one of the more important uses of hydraulics in motor vehicles. Hydraulically operated brakes are much more responsive and deploy very quickly compared to electric brakes. Although there is an argument for electric motors being used to achieve regenerative braking in electric and hybrid vehicles, these systems still use hydraulics for the quick action that is required when the brake pedal is pressed. ABS systems also rely heavily on the speed with which hydraulic brakes act; a miniature hydraulic power pack controls the system to deploy the brakes up to sixteen times per second in a skid situation, a speed which cannot be achieved by electric actuators. Mechanical brakes have a strong future in motor vehicles for safety reasons, and this will remain the case until electric actuators can replicate the speed at which a hydraulic system can function.
Gearboxes have been hydraulically operated since the early 1940s, when General Motors introduced the technology to its range. Although they were first developed in the 1920s, it took a while for the new design to be accepted and fitted in the new cars they were producing, but very little has changed since, apart from the introduction of solenoid valves in the early 2000s. Electric systems are now integrated into the control of the gearbox, especially for the twin clutch, but the mechanics at the centre of gearbox function are still hydraulic. This is one of the areas in which electrics will really have to try hard to oust hydraulics, and the only way hydraulics will be replaced here, may be if an engine can be developed where a gearbox is no longer needed.
Motor vehicles have used hydraulic dampers in suspension systems since the humble leaf spring fell out of favour. Even though some modern suspension systems (which allow the driver to adjust the settings for a particular driving style or road type) use electrics to adjust the shock settings, it is still hydraulics that effects the suspension action. Even electric vehicles use hydraulic suspension, as it is the best solution, and despite some manufacturers looking to recover energy from bumps in the road through an electrical suspension system, the complexity of such a system is not worth the small amount of energy that may be recovered, and certainly not at the cost of replacing a very capable suspension solution with something more expensive and difficult to fix.
Power steering used to be a hydraulic aid to assist drivers in steering and parking; right up to the 1990s there were still cars on the road that did not have power steering and anyone who has ever driven one, will attest to the huge difference that power steering makes to the driver. The first power steering systems used hydraulic pumps to provide the driver with extra power, but these have long since been replaced with electric motors. Self-parking cars are already widely available and these would not be possible without electrically operated steering. Power assisted steering is one area where hydraulics has already fallen out of favour and electrics have taken over.
Hydraproducts' miniature and micro hydraulic power packs are ideal for the automotive industry, and are perfectly suited to use in suspension, braking and power steering systems. Although there are some areas of automotive engineering where electrics have taken over, the key areas mentioned above are safe for now. Other areas have seen a better integration of electric and hydraulic systems, with the benefits of each being user harmoniously to affect the best system possible. As new designers emerge into the automotive market and look to shake things up, we may see electrics replacing hydraulics at least in the design and testing stage, but the reliability and relative simplicity of hydraulics means it will always have a place in the automotive industry.
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.
Hydraulic Power Pack
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