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A question we are commonly asked here at Hydraproducts relates to DC motors and the typical RPM these units normally run at. The answer to this question is simple, and heavily dependent on the load applied to the motor.
A good starting point is to look at how much pressure the system requires. This is often the least flexible parameter, as it will determine such things as the amount of load that can be lifted.
The flow rate is the next process that should be taken into account. This determines the speed of an operation and is typically more flexible.
With knowledge of these two factors, DC motor characteristic curves can then be used to determine which motor and pump combination best suits the application. To help you understand these curves and how to interpret them correctly, please refer to our previous blog on DC curves here.
The other important criteria on the curves is the duty cycle, S2 rating. This is a function largely determined by the current draw (Amps) and the physical ability for the motor to dissipate heat. So, the larger the motor size, the more easily it will radiate heat and the longer the S2 rating could be.
Whilst this seems a long answer to a simple question it is the only full explanation to what is the rpm of the DC motor.
Hydraproducts hosts a user-friendly product configurator which helps to tackle this process effectively. The user can spec their motor with options ranging from 500Watt to 3kW with motors over 1800Watt coming complete with thermal overload to help limit brush temperature inside the unit. Pumps and other accessories can then be added to the unit all the while the configurator works to ensure that all components are compatible with one another.
To see the Hydraproducts configurator in action or to simply learn more about how it works and try out different custom fitments, please click this link which will take you directly to the configurator itself.
AC motors run on alternating current delivery, exactly as domestic electrical power is delivered to the home. Both the voltage and frequency are different across the world, and appliances designed for sale in a particular country must be able to cope with the power supply in that area, as using the wrong type of appliance with the wrong power supply could cause a fire or electrocution. It might be annoying having to take travel adaptors to different countries (especially so if you forget it with you!) but there is a very good reason for that!
Thermistors in AC motors serve a vital function preventing the unit from overheating by limiting the input current and initiating shut off systems when overheating is detected. Thermistors are thermally sensitive resistors which act when temperatures change, either decreasing or increasing resistance. A PTC (Positive Temperature Coefficient) thermistor increases resistance as temperature goes up and are used to protect against surges in current. An NTC (Negative Temperature Coefficient) Thermistor decreases resistance as temperature rises and is used in temperature sensors, such as toasters, freezers and commercial food processing equipment.
PTC thermistors in AC hydraulic motors can be located just after the power input in order to regulate current if the motor starts getting too hot while still maintaining operation. The feedback from the system can affect a surge in cooling activities or alert the operator to shut down the machine in the event of serious overheating. In environments where temperature increases could lead to a potentially explosive atmosphere an AC motor with PTC thermistor regulation is ideal, as the AC motor produces no spark that could ignite any material and the PTC system can ensure the system is shut down before dangerous temperatures are reached. An NTC thermistor could be used to control the action of a cooling system to ensure that the correct temperature is achieved and maintained during motor operation.
Another thing which makes AC motors ideal for use in potentially hazardous environments is the ease with which they can be isolated and contained, generally rated IP55 as standard. DC motors are much harder to house in a sealed protective casing, so an AC motor is the obvious choice. IP (Ingress Protection) ratings denote the ability of any piece of equipment to withstand material and water entering it. The first number given relates to the ability to withstand solids from hands (1) to total enclosure from even minute dust particles (6). The second number relates to the waterproof factor of the item, from dripping water (1) to immersion beyond 1 metre deep (8). The highest level of protection is IP68, and the lowest would be IP00, although it is hard to think of any item of equipment that could realistically achieve that rating! AC motors are therefore ideal in dusty, dry environments where contamination and heat are present.
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.
The trailer industry relies heavily on hydraulic power for a range of applications be it car trailers, livestock or heavy machinery transportation. This is primarily because of the proven reliability and strength of hydraulic systems as well as their ease of operation and user friendliness.
As trailer applications use hydraulics in different ways, we have provided a breakdown of some common types of these below:
Having to operate in a range of environments, plant trailers are the first choice for transporting construction grade machinery such as diggers and other machinery.
The hydraulic tilt mechanism allows a low approach angle for loading and have advantages over other types of plant loaders as they can cater for plant vehicles with low ground clearance.
Typically available in a range of different styles including all-purpose trailers with a single axis which are suitable for agricultural and building machinery and for vehicles weighing over 3.5 tonnes, twin axle, auto tilt platform trailers are commonly used. Custom made tippers are available that cater for alternate platforms such as scissor lifts.
Regarding the operation of the trailer, the trailer deck typically extends backwards, initiating the lowering of the tailboard which locks on a horizontal plane. This enables the body to balance above the pivot point, which can then be angled allowing the machine to be moved on to the trailer. The pump valve can be closed off to allow the body to remain in a raised position in order to load other items; re-opening of the valve will then lower the body. The body is released when unloading so the tailboard will lower allowing the machine to be loaded up on to the ramp and the body will then tilt, using hydraulic damping, and the machine can be driven back off.
Coming in a variety of sizes and shapes, car transporters are typically enclosed units that protect their contents from the outside environment are and a popular solution for those wanting to transport vehicles around the country or cross continent. They provide a working platform for any owner and the low bed chassis they typically come with provides a stable and safe towing base.
They commonly feature a hydraulic-tilt bed operation, together with a loading ramp/door and popular materials used in their construction include steel and aluminium. Some specifications also include remote control electric winches and various loading and securing equipment as optional extras with the package to aid in getting the vehicle on-board.
Commercial tipper trailers
These units are primarily used to carry commercial and agricultural materials and are found in abundance in the construction industry where they are regularly seen tipping earth, bricks, mortar and other materials.
The trailers are built to have a high clearance for site access but also a low centre of gravity for optimal loading and towing performance. They have a solid and robust build due to the weights of materials they carry on an almost daily basis, and come with a single function high tilt mechanism which allows approximately 60° of tilt to ensure that any materials contained will disperse successfully.
A hydraulic power pack is typically installed in front of the hydraulic arm within a protective case and a pendant hand controller controls the tilt operation of the trailer.
Suppliers of these units comply with health and safety regulations by installing audible warning systems when the trailer bed it raised and lowered to enable operators to work safely and effectively.
Hydraproducts supplies a range of DC power packs complete with 12 or 24VDC Motors containing single and double acting valves primarily for use in tipper applications
As well as manufacturing the power packs themselves, Hydraproducts are also able to tailor their design for a bespoke fit to the majority of applications using state-of-the-art 3D modelling technology.
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.
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.
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