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Hydraulic motors and pumps, like all hydraulic equipment, need adequate lubrication to function properly. A lack of lubrication causes moving parts to grind against each other, causing wear and tear and also generating heat – both things which cause severe yet preventable damage to the equipment. Unfortunately, many people operating hydraulic machinery are unaware of the science behind it, and do not understand why dry starting a motor or pump is a bad idea, especially if they have been told that a motor or pump housing will fill with hydraulic oil during operation. Of course, this will happen, but not immediately on starting – it can take several hours for a decent level of fluid to build up in the housing to protect and lubricate the machine, and in that time irreparable damage is occurring. As Alexander Pope's famous misquote states, “A little knowledge is a dangerous thing” (the original quote was “a little learning is a dangerous thing” - for those who are interested).
This is one example of preventable damage that can be addressed through basic training. By instructing pump operators to check the fluid levels prior to starting and explaining the dangers of not doing so it is possible to improve and build upon the knowledge the operators already have, which helps empower staff to learn more. The simplest way to check is to remove the top-most connection on the pump or motor housing. If oil comes out of the seal, then there is enough hydraulic fluid in there for the equipment to be started. If no oil comes out, then the housing should be filled with the same hydraulic fluid that it uses to ensure proper lubrication before starting.
It should go without saying that when a pump is changed or drained for repair that clean hydraulic oil should then be flooded into the housing before the motor is started up again. Unfortunately, the misunderstood concept of a hydraulic pump filling its own housing is all too common and sometimes this misinformation prevails, leading to much shorter component life than expected, higher repair and replacement costs and unexpected downtime, all of which are undesirable consequences of taking shortcuts or making assumptions about the speed at which a hydraulic pump will fill its own housing.
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.
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.
We recently had a motor brought to our attention that had failed after only 600 hours of service. Having been expected to have a service life of over 7,000 hours, this seemed particularly strange. What could cause such a negative result? Upon inspection, it became evident that there was not enough lubrication of the bearings in the motor. In fact, there was hardly any oil in there.
Unfortunately it’s a mistaken belief that the oil that is circulating through hydraulic components is enough to maintain all parts of a hydraulic system. This simply isn’t true and each component should be taken care of and given attention in its own right to prevent this type of mishap from occurring.
In this situation, the case of the hydraulic motor should have been filled with hydraulic oil when it was installed, before the case drain line was connected. Without any oil in a piston-type motor, it’s almost guaranteed that it will fail prematurely upon starting.
Although it could be possible that the motor may have some hydraulic oil in it caused by internal leaking that is unlikely to be the case without the motor or the pump having been damaged. Until the component fails, that damage will not be known about – and this could take anywhere between 100s and 1000s of service hours to be discovered.
Our customer got back to us and told us that the warranty claim was rejected for this component. It was not installed properly, so the customer had to handle the expense of getting it repaired himself. It can be very costly to fail to install or commission components properly.
Although we aren’t a manufacturer of standard hydraulic systems, we do have some experience in how to maintain and take care of them. However, our speciality is mobile hydraulic systems. If you need to find out more, contact us today.
For most hydraulic applications, induction type variants are commonly used comprising of single phase to 3 phase motors.
To answer this question, we need to look at the type of application you are using and its function. So, for example, if you need a motor for a commercial vehicle application such as a tipper, tailift or trailer the DC motor will suit your needs, whereas AC motors are more commonly found in car lifts, security barriers and dock levellers.
It is therefore always necessary to specify your end use application first when enquiring about which motor you require.
One important fact to remember when positioning your electric motor on a power unit is its location away from other components. It is always recommended to leave sufficient space to allow the motor to breathe effectively especially if your system will be running high temperatures.
As well as the motor mountings, the general level of the ground the power unit stands on should be even as any kind of tilt could affect the motor should it suffer any short circuit forces while operational.
Electric motors are typically configured to run to temperatures from -20C up to +40C and the information on the motors running plate should be strictly adhered to.
• Take care to avoid rotating parts on the motor whilst it is in operation
• While the unit is energised it is imperative that the terminal boxes are not touched or opened as this could lead to a safety hazard
In order to maintain the reliability of the motor, manufacturer service schedules should be strictly adhered to and individual motor components such as seals and bearings should be regularly inspected for any wear or damage and replaced as necessary.
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.
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.
Hydraulic Power Pack
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