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The basic idea of an oil cooler in an hydraulic circuit to dissipate the energy losses that occur in the system is simple. The selection of an appropriate cooler, its sizing and position within the circuit are not so straightforward.
High temperatures affect the composition of an hydraulic oil, its properties and life. The chemical stability of an oil is measured mainly in terms of its resistance to oxidation. When oxidation occurs, oxygen combines with oil molecules to set off a chain of chemical reactions that create soluble and insoluble products of degradation. As a result the oil becomes darker in colour, its viscosity and acidity increases and gums and sludge’s are deposited in the hydraulic system. The tendency of the oil to oxidise is greatly increased by high temperatures, and by the effects of air, water and certain wear materials.
Although slight oxidation is not harmful, problems are encountered when the level becomes excessive. For example, the service life of the oil would be shortened, the system would be exposed to corrosive attack, the system components liable to sluggish operation, and the ability of the oil to separate from water and air reduced.
In industrial hydraulic applications it is usual for systems to operate with bulk oil temperatures of around 50 – 60 degrees C. In mobile duties rather higher temperatures may be encountered, of 70 degrees C and above. Temperature has a very major effect upon lubrication through the change that it produces in fluid viscosity. For an increase in temperature of 20 degrees C the viscosity of an oil may typically halve. Manufactures of hydraulic components specify a recommended viscosity range for the oils which may be used with their products. Fairly representative figures for the common hydraulic oils would involve a minimum viscosity of around 10cs and a maximum of several hundred cs. Normal working levels would typically be in the range of 20cs to 40cs.
Guidance about probable life of oils is very difficult to give, since it is affected both by the condition of the hydraulic system and the harshness of the working environment. Under good operating conditions an oil may last for tens of thousands of hours, whilst under bad conditions its life may be a matter of a few thousands of hours or less.
Although this blog is concerned with oil coolers, sometimes a neglected consideration concerns the operation of hydraulic systems from a cold start. In adverse conditions where low initial temperatures may be encountered it is usual to provide a heater in the oil reservoir.
Energy is dissipated as heat within an hydraulic system principally as a result of the pressure losses associated with the fluid flow. Losses occur through pipe friction, the effect of control elements such as pressure relief valves, pressure reducing valves, orifices and flow control valves, and through leakage and mechanical friction. The latter factors being particularly important in pumps and motors.
Correct positioning of an oil cooler within an hydraulic circuit requires identification of the major sources of heat generation and, within the bounds of physical constraints, the most advantageous location to dissipate the heat.
Types of Oil Cooler
The two principal types of oil cooler employ either water or air as the cooling medium. Where an adequate water supply is available the water type is commonly used. It has the advantages of compactness and of being less susceptible to changes in ambient air temperature. Water flows through the tubes and oil across the tubes, the latter guided in its flow path through the shell by baffle plates. The maximum oil pressure which the cooler can be subjected to is limited by the shell, a fairly typical figure would lie in the range 15 – 30 bar. The pressure drop associated with the oil flow through the cooler is usually small, of the order 1 bar.
Sometimes overlooked is the practical detail of fitting a strainer to the suction of the pump providing the water flow. Debris restricting the water flow through the cooler is one of the most common problems that arise in operation.
The air blast cooler in contrast is of lighter construction, and for the same heat dissipation is larger. Oil passes through the tubes of the cooler, which are usually finned to aid heat dissipation, and air blown over the tubes by a fan. The operation of the air cooler is sensitive to changes in the ambient air temperature and care must be taken in its selection to allow for this effect. The maximum allowable oil pressure is typically lower than the water type, a figure of 7 bar being representative. One of the most important applications of the air blast cooler is in the mobile industry.
For both types of cooler automatic temperature controls may be used where it is desirable to maintain the working temperature of the oil within prescribed limits. For a water cooler a commonly used technique is to employ a thermostatic valve to control the water flow, whilst for an air cooler temperature regulation can be achieved either through the intermittent use of the fan or through variation of its speed.
Here at Hydraproducts we have a wealth of experience in selecting the correct cooler for a system, for more information on this subject please call the sales team on 01452 523352.
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 hydraulic power pack 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 in hydraulic power packs.
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 .
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.
How to read hydraulic circuits
Hydraulics symbols are an essential component of hydraulic circuit diagrams. Knowing some of the basic principles will help understand a wider range of symbols. Explaining the common ISO1219 symbols enables a complete hydraulic system to be followed:
1. Hydraulic Pump
Hydraulic pump produces flow. Oil is pumped from the hydraulic reservoir into the system. The basic symbol for a pump:
A fixed displacement pump is the simplest type and has a fixed output for each revolution of the input shaft. Modifications to this symbol describe the variable displacement pump. The types of control circuits show how the output is varied.
Filters clean oil entering the system, and are used in various places within a system. They protect hydraulic valves and pumps. Suction filters are placed at pump inlets to ensure only clean oil enters the system. Pressure filters can be placed throughout system. Return filters are common and filter oil returning to the reservoir.
3. Pressure Relief Valve
Pressure in a hydraulic system should be limited to control the force any motive devices produce and to ensure the safe/design limits are not exceeded. A pressure relief valve symbol is normally shown as:
A pressure relief valve or PRV passes fluid from an area of higher pressure to a lower pressure (typically the tank). Hydraulic pressure shown by the dotted line acts as a pilot to actuate the PRV by moving the arrow across the box. This happens when the pilot pressure produces an internal force equal to the spring load the valve begins to open and pass flow.
4. Check Valve
This valve is a one way valve that prevents flow in one direction. The addition of a spring ensures the valve will only open when this pressure is exceeded. Dotted pilot lines can be added so that pilot operating pressures can be used to open the valve and allow flow in the reverse direction. Commonly used to hold pressure in a hydraulic cylinder.
5. Hydraulic Reservoir (tank)
Hydraulic systems all have a means of storing hydraulic fluid. This is referred to as the hydraulic reservoir. Hydraulic reservoirs are shown as:
Vented hydraulic reservoirs are common place, but sealed systems can be found ion aerospace and marine applications. The return lines shown indicate the position above or below the oil level.
6. Directional Control Valve
Hydraulic fluid flow is controlled by a directional control valve. Commonly consists of four parts, valve body, spool, actuator, and springs. The spool is moved with respect to the valve body, this opens and closes internal flow galleries to control fluid flow. Various types of actuators provide power to shift the spool and springs are normally used to return the spool when the actuator is de-energised.
Look at the typical three position four way valve:
How to read directional control valve symbols:
a. Each box in the valve symbol represents a possible valve condition. In the three position valve above there are 3 possible conditions controlled by the actuators.
b. Number of ways tells you how many hydraulic connections could be connected to the valve.
c. Actuators always push and never pull the spool.
d. The box furthest away from the actuator is the normal or de-energized position, and is the position where the circuit connections are drawn. In the above valve this is the middle position.
7. Hydraulic Cylinder
Hydraulic cylinder or actuator uses hydraulic power to generate mechanical force. A hydraulic cylinder is shown as:
A double acting cylinder (above) has two ports and is therefore powered in and out. Single acting cylinders have one port and would typically be used for lifting applications.
We hope this gives you a useful introduction to hydraulic circuits. For a full list of hydraulic symbols can be found in ISO1219, or contact www.hydraproducts.co.uk for more help.
In this blog, we look at air coolers and how they are used to disperse excess heat from a hydraulic system to help retain system efficiency and reliability.
As you may well know, excess build-up of heat in a hydraulic system can cause a multitude of problems including fluid decomposition, damage to seals and other system components such as bearings.
Hydraulic air coolers are found in a wide range of applications covering various sectors including agricultural, industrial, manufacturing and mobile machinery. Air coolers are essential if your system has been designed to operate at an optimum hydraulic oil temperature, as they ensure that this temperature remains at its correct level.
The larger the system, the more likely it will need a cooler, unlike smaller systems which can harness the power of natural convection due to them typically running at lower operating temperatures. For example, if working with mobile equipment such as material handling, industrial process machinery or construction based applications where hot fluid can be a big issue, it is imperative the right type of air cooler is selected to control temperatures. This leads us on to our next area, which is the type of cooler that should be considered depending on the application it will be used for.
Selecting the right type of air cooler for your system
Identifying the correct specification of cooler for your system is a vital process that needs a lot of research to back up your final decision. We look at several key areas that will influence your selection:
Environmental factors – This can largely effect the amount of work a system has to do, with high environmental temperatures taking more out of a system, thus a bigger cooler being needed to correctly regulate temperatures. Likewise in colder climates, less cold air feed is needed for optimal performance
Temperature cycles – Machines often go through various temperature cycles during their running period, so this has to be taken into account when cooling measures are looked at so a best fit can be found. The timescales of temperature change must also be factored in so if for example, if a system tends to run at higher temperatures during a long cycle, a higher level of cooling is required to counter this.
Available space – With the complexity of some systems and any bespoke extras that have been added, the amount of space needed for fitment of an air cooler can vary greatly. This is something that should be looked at closely during the planning stage of a system design so as to ensure that there is enough space to accommodate a suitably sized cooler unit.
So, with all the factors taken into account above, you will hopefully have a clearer understanding of what to look at when choosing an air cooler, and at Hydraproducts, we can guide you through your bespoke design process and recommend best fitments for your system.
Feel free, click on the following link, to visit our new Hydraproducts Components Division page on our website where you can learn more about our Air Cooler range.
Injuries are a relatively common occurrence for people working with hydraulics, especially those working in the maintenance and/or repair of hydraulic equipment. The most serious injury is a pressurised fluid injection, but accidents can also happen with moving parts when the stored energy in the system is not released before inspections and repairs are made. Unfortunately, it is not routine for tags and gauges to be used to denote places where energy is stored. The engineer must study the schematic thoroughly before starting any investigative work, in order to be sure that there is no danger of anything moving while they are working on the machinery.
If pressure gauges were used to show the residual pressure left in moving parts the engineer could utilise the pressure relief valve to release the stored energy and make the hydraulic equipment safe to work on. Relieving pressure stops anything moving of its own accord, which could be dangerous, and also reduces the risk of high pressure hydraulic fluid injection injuries, which can be fatal.
When inspecting for leaks in seals and hoses, it is important that pressure is released before checking but even then, it is not advisable to check with your hands. Instead, perform a visual inspection and look for other signs of leaks, such as fluid on the floor or on parts of machinery that sit underneath the suspected location of the leak.
Hydraulic equipment can be just as dangerous as electrical circuits for those investigating and repairing faults; but electrical work is governed by strict regulations which include the use of lockout tags and labels denoting the location of potentially dangerous components. Hydraulic equipment is not covered by such stringent regulations and as such, it is at the discretion of the designer whether pressure gauges and safety accessories are included in the machinery at the time of building. These items can be retrofitted by the owner, but this is not often done and this means hydraulic engineers must spend a lot of time reading manuals and schematics to understand where the dangers lurk, before being able to safely get on with any repair work.
Just because it isn't legally required, there are no good arguments for overlooking these safety precautions, but several reasons why they should be addressed., such as: reduced downtime on repair and maintenance tasks, a reduction in the potential for workplace injuries and a speedier repair. All effected by removing the need to spend time studying diagrams to pinpoint potential dangers. Employee health and safety is of paramount importance to employers, and this could well be the biggest reason why hydraulic equipment should be fitted with pressure gauges, relief valves and lockout tags, to prevent tampering with settings and to alert engineers to the locations to address first.
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