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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.
We have said it before and we will say it again: hydraulic power really is one of the most important technological advancements of all time! It frequently helps our society run and function far more smoothly and efficiently and most of us would not even realise. However, we are sure that nearly all of us would notice if the world suddenly stopped using hydraulic power because the world would be a very, VERY different place.
Hydraulic power is used in so many everyday applications from mechanical lifts to bulldozers and now even in our braking systems. In this article we are going to share with you, in our opinion some of the most interesting facts about hydraulic power out there.
All hydraulic power systems will contain four core components. These include the fluid reservoir, which quite simply houses the fluid, a pump to spread the fluid through the system, a cylinder to convert the fluid movement and the valves which control pressure and flow.
The word hydraulics originates from the Greek word ‘Hydros’ meaning water. This is because water was the first liquid to be used in hydraulic systems.
Hydraulic pumps are used by NASA’s in their space shuttle. These pumps operate at a whopping 3600 revolutions per minute and each one could supply hydraulic pressure of 3050 PSI.
For hydraulic power to work it must flow. If the flow encounters any block or opening, then the pressure will drop. For hydraulics to work, it is vital that the flow is unrestricted.
Hydraulics was discovered in the 17th and 18th century by two men Pascal and Bernoulli. Their principals led Joseph Bramah in the late 17th century to create the first hydraulic press. This press was used to pump beers from cellars to the taps in public bars.
Hydraulics are not the only way to transmit energy, many industries also used mechanical, electrical and pneumatic energy. Mechanical energy is from crank mechanisms, shafts and linkages, electrical is from electric motors. Pneumatics is the closest to hydraulics but instead of using fluid it used gas.
Without the pressure, you would not have hydraulic power. Hydraulic systems contain fluid that is under intense pressure. Pressurised fluid is what produces energy.
Did you know that not all hydraulic systems are the same? Generally you have two types of systems, firstly there is an open centre system and secondly there is the closed centre system. The open system has a varied pressure with constant flow and closed systems have constant pressure and varied flow.
Many people believe the common misconception that oil is pulled through the system, this is not the case. Hydraulic power is created by air pressure pushing the fluid through the system not pulling.
Finally, our last fact is that hydraulics can produce three different types of energy. You have kinetic energy which is caused by moving fluids, you have heat energy which is produced by resistance to the flow and lastly you have potential energy which is caused by the pressure.
There are so many other interesting facts about hydraulics but we really could be here all day.
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 .
The purpose of check valves within Hydraulic Power Packs and Systems is to allow fluid to pass in one direction but to prevent it from travelling the other direction, or doing what is known as a reverse flow. The device is usually added to a pipe to prevent oil from flowing backwards. When necessary the valve will close so that all backward movement of fluid is stopped.
The hydraulic check valve has two ports. One is the inlet for the hydraulic fluid to enter and the other is an outlet. They will both operate in combination with the motor, cylinders and hydraulic pump. The valve controls the flow of fluid for the correct operation of equipment.
Hydraulic valves are available in a number of different designs. They may look like a poppet, a disc or one of the ball or plunger types. This will depend on where and how they are being used as to what style and size is used.
Most often you’ll find hydraulic check valves used in application such as braking systems, construction tools, lifting systems and other hydraulic systems. They are installed in systems where the backup of fluid could cause serious issues.
For example, if oil flowed backwards through a pipe, it could empty a hydraulic system back into the equipment reservoir. Even when the machine is turned off the hydraulic valve can prevent fluid from flowing through the system, keeping it full ready for the next time it is operated.
Dual Pilot Operated Check valves (abbreviated P.O.C), are check valves that can be opened by an external pilot pressure. Flow is blocked in one direction as per a standard in line check valve, but it can be opened when sufficient pressure from a pilot line is applied to the third port. The pressure required at the pilot port is normally only 1/3 of the pressure locked within the cylinder. This is determined by the Pilot Ratio (3:1 and 4.5:1) are normally available. They are regularly used with double acting cylinders to lock the system when pressure is switched off, either intentionally or by accident or failure. They can be fitted directly between ports on a ram or incorporated into a power manifold block or module. It is preferable to mount them directly to a ram with “hard” pipework as this increases the integrity of the device. If the pilot check is only required or desired on one side of a cylinder then it can be on the A or B sides, referred to pilot check on A or B.
Regular applications for pilot check valves are rear loading ramps on commercial vehicles. Balers and compactors where the load needs to be held while baling occurs. Security access bollards and blockers to stop the creeping down when the system is at rest. It is important top note that POC are not best suited to applications that have a load that that will over run when they are reversed.
Flow control valves regulate the flow of a fluid and take many forms:
Fixed orifice: Basically a hole in a tube or an insert that fits into the hydraulic line, restricting the amount of fluid that can pass through it for a given pressure.
Adjustable orifice: The size of the effective orifice is adjustable. Common forms are inline and barrel type where the body of the valve is twisted, needle valves for fine adjustment on low flow systems. When set the adjustment can be locked. These are regularly used on lifts or tipper applications where the load is uniform.
Pressure compensating: When a load such as a cantilever passes through an arc the system pressure can vary. This causes the speed of the cylinder to change leading to potentially undesired results. To overcome this pressure compensating valve account for changes in pressure and delivers broadly uniform flow to the hydraulic actuator. In a scissor lift a high pressure is required at the initial raise and decreases as the mechanical advantage increases. The reverse is true when lowering under gravity so a compensating flow control is suited here.
Reverse flow check: On a single acting power pack the pump and motor combination are optimized to give the desired lift speed of the hydraulic cylinder. The flow control valve has an integral bypass line that allows full flow in the out direction, through a built-in check valve. When lowering the full flow oil path is checked and forced to go through the flow restriction allowing controlled descent of the cylinder.
This consists of two valves in one block. When operating a double acting ram the extend and retract speeds will differ, due to the different fluid volumes. From our control valve full flow is permitted through in one direction whereas the other side is flow controlled and/or vice versa, in this way the different valve settings will optimize the actuator speeds. A common example of this valve configuration would be a rear door on a horsebox where the door will need to close much more slowly to prevent shock and noise.
A relief valve is an important control device in virtually every hydraulic system. They protect the overall system from generating a pressure that could cause mechanical failure. It is a mechanical valve that requires no external input other the applied pressure. When this excess pressure is relieved it re-seats to allow normal operation to resume. The most common type comprises a spring and plunger pushing onto a seat. If the pressure exceeds that of the spring force the oil is spilled to a volume usually the oil reservoir. The springs have adjustment ranges for example 20-100 bar and the valves can be housed in cartridge, module or designed directly into an aluminum or steel hydraulic manifold.
A hydraulic circuit may have multiple relief valves, one at the power pack end to protect the pump, another may be fitted onto a control valve circuit to relieve an induced load caused by external mechanical forces. If a hydraulic cylinder requires different relief valve settings on it full bore or annulus side then a dual relief valve module can be set to handle these needs. On the annulus side the area the oil is acting upon is smaller requiring higher pressures to exert the same force as the full bore side hence two relief valve settings are needed. One example of this is a hydropower generation sluice gate operation where something jammed in the gate such as log stops it closing.
Some terms associated with relief valve operation:
Overshoot: The pressure reading when a relief valve operates to bypass fluid. (It can be two times the actual setting.)
Hysteresis: The difference in pressure when a relief valve starts spilling some flow (cracking pressure) and when full flow is passing.
Stability: pressure fluctuation as the relief valve is bypassing at its set pressure.
Reseat pressure: The pressure a relief valve closes at after it has been operating.
Counterbalance valves are fundamentally a relief valve that is fitted in an application to generate back pressure in a system. They are normally used for ‘counterbalancing’ a load to stop it from running away during lowering. The valve is usually set at 30 percent higher than the pressure induced by the load.
Figure 1 Counterbalance valve circuit.
A built in check valve allows flow in the reverse direction (i.e. to by-pass the counterbalance valve when lifting the load). It should be noted that both sides of the valve will be subjected to full pressure, this is not possible on all relief valve designs. In Figure 1 the counterbalance valve has an integral check valve. When counterbalancing the return path must have a low back pressure to tank, as this will be additive to the valve setting.
Hydraulic filtration is a vital component of keeping a system running smoothly.
For example, did you know that up to 75% of failures with fluid power can be attributed to contamination? With the use of hydraulic filters, contamination damage can be significantly lowered which can not only cut down on expense but lower that 75% drastically.
If you’re looking to save costs from less downtime then it’s also time you looked into what a difference hydraulics filtration can make for extending the life of your equipment. Running your system optimally is essential when it comes to cost saving, but protecting its longevity is also a critical element in running any business efficiently.
Muck and dust can destroy a hydraulic system, that’s why it’s essential to make the best use of hydraulic filters. You wouldn’t even be able to remove that dirt yourself, as it’s likely to be dust that is so fine that you won’t be able to see it without the use of a microscope. Dirt has the same detrimental effect as sandpaper or gravel and not only will generally deteriorate the system, but it could even destroy it.
However, through the use of a hydraulic filter system you will be able to maintain control over the level of contamination and by doing so reduce the failure of systems by as much as 75% just be removing that dirt.
Hydraulic parts are expensive. Combine that with down time and having to keep engineers on hand to fix worn components and that’s a lot of expense to deal with. Putting filters into place can even save costs by increasing how long the hydraulic fluid will last.
Degradation of fluid – hydraulic fluid that contains fine metallic particles can degrade rapidly through chemical breakdown. Without protecting against this, there could be issues such as slippage, internal leakage, corrosion or sticking parts.
Scoring of surfaces – this can occur when particles get trapped between surfaces of seals
There’s no doubt about it, but …
· System performance is affected by dirt levels
· Hydraulic filters can control levels of dirt. Without using this management method, the system will get dirtier and dirtier until it fails.
In fact, hydraulic filters are the only way to control how much dirt is in fluid. Without them you will be forced to change out the hydraulic fluid regularly, which can be a time consuming and costly event.
Hydraulic system dirt particles are incredibly small. In fact, they are so small that they cannot be seen by the human eye – and 98% of hydraulic fluid has some dirt in it.
Engineers have found that when it comes to size of particles in samples taken from operating systems, the smaller the particles, the more dirt there is in the system.
So where do these particles come from that we have to work so hard to deal with?
In order to have an idea of what goes on inside the closed system, let’s examine where these particles come from.
Instead of enjoying the typical 20 gpm that is the measurement of a pumped flow from a 2000 psi system, you can expect to see something in the region of just 10 gpm. Although your pump will still produce for you, you’ll discover that the degradation results in just 50% efficiency and you should als be prepared to experience extra heat and other unwanted issues.
As with any hydraulic system, there is an optimum level of cleanliness, but there is a point where you cannot get any better performance out of the system by improving the quality of the fluid. However, with the use of hydraulic filters you should be well set to extend the life of your machinery.
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