Get in touch today to discuss your requirements
Call: (+44) 01452 523352
Counterbalance valves may seem an obvious choice in preventing an accident of this type, but they cannot be relied upon. An engineer was recently injured when a machine he was working on dropped i’s load as he attended to a leaking rod seal. Although he took all the necessary precautions of lowering the load to remove pressure, he was startled and hurt when a high pressured jet of fluid fired at him from the fitting. The counterbalance valve had trapped pressure and caused this situation.
It’s essential that all hydraulic equipment is designed with safety in mind, in particular with de-energisation. High pressure oil jets can leave to serious injury or death as they can penetrate your skin. Safety should not be taken lightly.
What do you need to know to keep yourself and other people safe in the workplace?
Keeping a load safe is dependent upon ensuring that the pressure of fluid is correct. If the pressure of it becomes too high, then it will want to give that energy to other surroundings, and it’s only the soundness of the components that will prevent it from doing so. It will try to escape any way possible and this includes through weak seals, valves or other points of plumbing failure.
The metering devices such as valves, flow controls and counterbalances prevent the fluid from running away. To demonstrate this, a cylinder that is installed with rod down, and tension under load will often have a meter-out configuration to stop the load from taking control of the cylinder
Although this is safe, there is still a risk of the pressure on the rod-side intensifying. If the piston seals get blown by this, then the load will drop.
Some engineers will use a counterbalance to avoid metering out errors from occurring. Although a counterbalance valve is considered to be the same a pressure valve, it is what controls the speed of an actuator. It will control how fast the cylinder moves, even if there is a pressure intensification.
Another situation that can cause a catastrophic failure and even personal injury is a leak in the cylinder hose or tube. If fluid in the actuator exits through a broken conduit, it is no longer able to hold up a load. In the event of a conduit failure, the counterbalance valve will prevent the load from dropping. Another safety function that will hold a load is a pilot-operated check valve. Although it will hold a load indefinitely, it will not be as smooth with control of load induced movement.
The essence of a hydraulic system is pressure. It’s something that is required to make the system as powerful and effective as it is. However, there are many reasons why pressure can easily rise including load spikes, ‘water hammer’, intensification and even thermal expansion. If there isn’t enough control over pressure, then components can fail and seals can give way – leaving the machine to be unsafe. It’s for this reason that the hydraulic system has so many different types of pressure control valves.
Damage can be prevented by limiting pressure with relief valves. They can control the pressure in the main system or in isolated sub-circuits. In some systems, it’s necessary for sub-circuits to operate at different pressure to others. This can be achieved through the use of the pressure reducing valve which is able to limit pressure downstream of itself. It is also able to reduce pressure in situations where the fluid has become too heated and therefore has increased its pressure. In some systems there are a number of valves that will work to ensure that pressure is limited to a safe level in every part of the machine.
In summary, it’s important to control both the pressure and the flow in hydraulic systems. It enables safe operation of the system and movement of loads. Safe employees are everybody’s concern.
Counterbalance valves are an area that many of our clients are interested in. We’re not really sure why, but it’s a fact. If you’re new to this field, then let’s get you on the same page.
Counterbalance valves operate as safety devices. If pressure is lost in a line going to the cylinder, then they will stop a load from dropping. They will allow fluid to flow the one direction into the cylinder, but will prevent it from coming back out again unless there is an inversely proportional pressure in the pilot line of the valve. Although it’s possible to swap this this valve out with a pilot operated check valve, the method of checking for proportion is what keeps movement smooth as the cylinder piston retracts.
With the pilot operated valve, there will be some ‘chatter’ as it retracts. Although the counterbalance valve is useful and widely popular, there are some concerns with it. For example, over in the USA there has recently been a safety alert issued on the Fluid Power Safety Institute website by Rory McLaren. It’s been discovered that the counterbalance valve can create a form of deception when pressurized fluid is trapped between the cylinder and the directional valve.
With regards to safety, we understand that there was an incident with an engineer and a leaking rod seal. Following all the necessary safety precautions, the engineer needed to lower the load by shifting the directional valve, then de-energize the hydraulic power unit. He then needed to remove the power unit from the application as he was guided by the company’s hydraulic system maintenance process. Imagine his surprise to witness a high-velocity jet of fluid shooting out of the fitting that he was loosening.
Assuming that the lowering of the load would take out all the pressure from the hydraulic line makes sense. However, the counterbalance valve being in the line between the valve and the cylinder can create problems. Even if the cylinder is in the rest position with the machine shut off the pressure setting in the counterbalance valve is at its lowest pressure.
Unfortunately in the above situation, the pressure was set in the counterbalance at 1200 psi which means that the shot of oil is going to be expected. Although the engineer was injured, he fortunately, wasn’t killed by it – although this is an outcome that would have been entirely possible. His action should have been to check that each of the lines were depressurized prior to opening them to atmosphere.
Here are our tips to ensure that you’re safe when performing this type of hydraulic system maintenance:
1. Take necessary actions and verify that the lines have been de-energised.
2. The written maintenance process needs to contain a step to safely remove any pockets of hydraulic energy in the system. If there is a chance that the pressure could re-accumulate, then take steps to check that isolation is in operation until you have completed your maintenance or servicing or until it’s simply not possible for pressurisation to occur.
3. Make it mandatory for all hydraulic system personnel to have lockout and de-energisation training.
4. Create a written safety process for both lockout and de-energisation of machines.
5. Schedule drills for de-energisation and lockouts to verify that all staff know what to do to make the machine safe to work on. Some situations can be more complex as more than one machine may need to be locked out for maintenance purposes.
6. Make it a punishable offence to ‘crack’ connectors in order to remove stored energy.
7. Don’t risk your life by tampering with a hydraulic machine that is not designed to safely de-energise. Don’t follow instructions to crack a connector as this could kill you.
8. When purchasing any new machines, look for those that have de-energisation functions or facilities.
9. Contractors will need to obey all safety rules and they should have a history of training and certification. This is particularly vital if they have been brought in for their skills and to mentor your employees. You don’t want your employees picking up any behaviours that are not considered to be industry best practice.
If for some reason you cannot remove the energy from the system, then call the manufacturer for guidance. This is not the type of situation where you can use guesswork, or you could even lose your life or health when pressurised oil penetrates your skin. Hydraulic systems can be dangerous with fatal consequences when not used correctly.
Although using high-pressure hydraulic systems is considered to be one of the safest methods of applying force, there are still some important factors to take into account. They are powerful tools and can take on any bending, lifting, pushing or pulling work that you need performed, but there are some important safety factors that need to be observed.
Surprisingly, one of the weak points of the hydraulic system when it comes to safety is that it is very easy to use. This can lead to complacency and in some cases abuse. As with any type of equipment use, there are rules to be followed and disciplines to observe in order to get the best from these machines whilst keeping yourself and others in the vicinity of the equipment safe from harm. Following these guidelines can also often ensure longer lifespan and greater efficiency of the machinery.
In the following passages we look at the different areas of safety that will need to be taken into consideration when dealing with high pressure hydraulic tools.
Just as with any equipment, it’s necessary to observe standard safety rules. This means that gloves, safety glasses, boots or safety shoes and a hard hat all need to be worn. As in any environment that can be hazardous, these should be considered fundamental necessities.
Although most engineers will take the most obvious precautions to avoid accidents whilst taking the longevity of the equipment life into consideration, most mishaps and issues will come from either not operating the equipment properly or not assembling it in the right way. It’s important to understand each function in addition to being clear how it works. Take time out to learn your machinery and how it works.
Lifting of loads that are over capacity is something that can result in trouble. Not only will the cylinders be at risk of damage but it can also result in bent plungers and blown seals.
Keep in mind the following points:
- Take an estimate of what you think the load will be, then apply a suitable safety factor.
- Keep in mind that some of your pumps will be equipped with relief valves whilst others won’t be.
- The use of a gauge will help to give an indication of which operating loads are safe.
- Your gauge should also be used to determine whether there is any pressure in the system before you make any changes or breaks in the hydraulic connection.
- Check your environment before you either advance or retract a cylinder.
Fundamentally, two types of cylinders are used in hydraulic systems. The single acting and the double acting.
Single acting cylinders may be any of these types:
· Spring return
· Load return
Double acting cylinders work with the use of hydraulics and advance and retract.
It’s important that you follow these safety guideline rules for cylinders:
- If you need to position the cylinder on the ground, ensure that the base is able to bear the weight of it. It wouldn’t be funny to watch your hydraulic cylinder disappear into soil. A jacking based should be used, or at least a steel or timber plate that will enable the load to be spread.
- The saddle should have the load spread across it, and not be point loaded.
- Stay clear of and be careful around any areas that are directly below a load that the hydraulic cylinder is supporting.
- Situate your cylinders in order to give enough clearance space for extension of them.
- Excessive heat is any heat that is above and beyond 65°C. This needs to be avoided otherwise packing will be softened and hoses weakened. If there is heat that is not avoidable, use either a piece of metal or a heat-resistant blanket to protect the cylinder.
- Keep oil connectors clean and wipe any couplers before they are connected. Dust caps are provided for a reason and that’s to keep dust and dirt out. If you choose not to use them, be aware that you’re likely to experience scoring of the cylinder walls and this can lead to the eventual failure of seals.
- Over-extending cylinders should be avoided as not all of them have safety stop-rings installed.
- If you need to add oil to the pump, check whether the cylinder is already extended, if it is be sure not to disconnect them. The trouble with having too much oil in the system is that your reservoir could become pressurised and blow. If it doesn’t blow it will rupture.
Hydraulic Hand pumps
Depending upon the speed and oil capacity of your system, there is likely to be a pump available for each cylinder. These may be power-assisted or they could be manual in nature. Those applications that are lower speed and where it’s necessary to have that added human ‘touch’ will usually have a hand pump. If the application needs faster movement, or the cylinder is particularly large, then it will use a power pump.
It’s essential that the pump valve is suitable for the cylinder. For example, with single acting cylinders, there is usually a pump that has a 2 way or a 3 way valve. This equates to one outlet. When it comes to double acting cylinders you’re likely to find a 4 way valve which means it has 2 outlets. It’s dangerous to use a 2 way valves in combination with a double acting cylinder.
Check the pump reservoir level before using. Fill using the correct procedures if necessary. Remember that pump hoses will shorten when they are filled with pressure, so ensure there is enough slack to handle this.
With regards to power pumps, you can expect to come across one of these types:
· Petrol / Diesel
It’s fairly obvious that hose failure can occur after heavy objects being dropped on the hose cause damage, but it’s surprising how this escapes the thoughts of many engineers. We often hear stories of how something was dropped but then it was a forgotten memory and the next thing the engineer knows, the hose has failed and there has been a hydraulics disaster.
Another strongly recommended tip is that hydraulic equipment should not be carried by the hose. Most of us are well aware of this, but you will need to keep an eye on any young apprentices who are as yet unfamiliar with the norms of operating hydraulic systems. There should also be an eye kept out for any sharp bends in the hose. The internal wire braids can be damaged from this type of event and this will weaken the set up and could result in leaks and at worst a lethal situation.
An essential fundamental when it comes to hydraulic system safety is to check all fittings, hoses and connections to ensure that they are tightened as they should be and that they comply with the amount of pressure that they will need to be able to handle with your specific system.
We generally recommend that hydraulic systems use oil that is suggested by the manufacturer. The system will usually have been manufactured around that oil and the creators know that it will perform best with that particular one. You will need to change the oil periodically. This will ensure that the system does not get damaged by dirty oil. Ensure that hydraulic oils do not touch your skin.
After you have finished using your hydraulic machinery, it’s time to get it ready for the next job. You will need to clean it before storing it. You can do this by wiping it down. You will also need to lubricate any parts that are exposed.
In conclusion, operating hydraulic systems safely entails using the right cylinder with the right pump and the right oil. Although these rules may seem obvious and safe, it’s surprising how many people fail to adhere to them and put themselves and others in danger. Hydraulic equipment is very powerful but it can also be very dangerous.
As we sympathise regularly with our readers, running hydraulic systems can be very costly. Not only can costs build rapidly from replacing damaged or worn components, but there is also system downtime to consider and to add to the expense.
If there is one deadly enemy for hydraulics, it’s contamination. In fact, contaminated fluids can be connected to more than 80% of all hydraulic failures. This includes all the related failures that can result including those of hoses, fittings, pumps and valves.
In fact, there is such a strong correlation between contamination of fluid and the lifespan of components that manufacturers of hydraulic and filtration products actually publish charts with the consequence predictions of not having inadequate filtration installed. Those systems that undergo rises in pressure will suffer from even more damage as contaminant particles make their way around the system.
Unfortunately the particles involved in hydraulic system contamination are usually far too small for the naked eye to see them. This is why it’s essential to use instruments specifically designed for contamination monitoring, otherwise a high system reliability cannot be expected to be maintained.
Although the operators and engineers who take care of industrial hydraulic systems are well aware of this problem, it’s only really coming to the fore of the mobile hydraulic system now. In this microcosm of the hydraulic world, there is still some time-based fluid maintenance going on. However, it’s becoming more apparent that this and spin-on filters are no longer enough to keep mobile hydraulic systems operating at their peak performance levels.
Quantifying contamination in hydraulic systems
Ideally every hydraulic system should have absolute filtration to capture both micro particles and those that are larger.
A Beta ratio of filtration will usually capture 99.5% of all particles that could contaminate a system. Alternatively the 1000 measurement will capture 99.9% of the particles. This will support the hydraulic system in enjoying a maximum service life. However, in addition to the Beta ratio, there are other considerations to ponder over when looking to keep the system clean.
How much dirt a filter can hold and how stable Beta ratio is will determine how well the filtration works out for the system. The best filters are usually cartridge-type that use a number of layers to help to maximise performance for all areas. Each layer will help the filter to either capture the dirt, hold it or to deliver the beta stability.
Another unexpected benefit of the cartridge-type filters is their ability to reduce how much loss of fluid there is when the filter is changed. This can keep go towards keeping costs down, whilst also lowering the impact on the environment. Although the cartridge type filter may cost more to buy, they deliver when it comes to protecting the system and cutting back on fluid loss.
With industrial hydraulic applications, cartridge filters are now considered to be the standard. They are also becoming more popular and widespread in the mobile market, which is becoming more sophisticated when it comes to components in addition to enduring rising costs.
Mobile Filtration Challenges and Solutions
Another area of concern with mobile hydraulic systems is that of space in the system to add filters and other components such as sampling valves. Quite often manufacturers will produce tank-top filters that can be integrated into the hydraulic reservoir, but sit out of the way. With global emission requirements becoming tighter, this trend is likely to accelerate in the coming years.
One issue that is unique to the mobile world is that of the cold start. It’s well known that any hydraulic fluid will thicken when sat at lower temperatures. This can increase the pressure drop for the filter element. The performance will take a downturn until the fluid begins to gain temperature and reaches the operating temperature level. Quite often the comment from an engineer will be ‘I started up and when I hit the level, nothing happened’.
Although it’s possible to install a large filter, it can add to the bulk and the cost of the system. Another work around is bypass the filter by adding in a pressure relief valve until the fluid is warmer. However, this can send contamination downstream. An approach that is less troublesome is to return the fluid to the reservoir as opposed to allowing it to circulate throughout the system.
In summary, as an engineer, the best move you can make is to identify and implement a fine filtration strategy that will enable your hydraulic system to run at its ultimate performance.
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.
Providing all the necessary diagnostic tools to a hydraulic system technician almost guarantees that the source of an issue will be discovered and remedied rapidly. However, as with any ill, prevention is better than cure. Using the diagnostic tools on a regular basis can identify any trends that could result in the failure of a component.
Hydraulic system fluid contains many answers
Quite often, it’s the hydraulic fluid that reveals the answers as to where potential problems will arise. For example, taking a fluid sample can provide a multitude of measurements including how much of the following are in the fluid in addition to any signs of oxidation which is typical of being subjected to too much heat:
There are some tools which can make taking samples easier such as a ply and sampling valve. It also means that you won’t further contaminate your machine by adding more contaminants to it.
The value of sampling fluid regularly twinned with the fact that hydraulic equipment is usually caked in some form of dirt or dust, does not make an easy marriage. It’s essential to keep that dirt out of your system and your sample. Engineers know that sampling from hydraulic systems is a risk that engineers have to take. It’s a risk to take the sample as there is a good chance that something from the surrounding environment could enter either the system or the sample. Nobody wants dirt, particles or even water in their hydraulic system.
The risk increases when it’s necessary to draw the fluid from the hydraulic motor. Unfortunately a tube must be inserted through an open port that is accessible once an access plug has been removed. This makes it possible for contaminants to enter the system or even to stick to the tube and then be inserted directly into the fluid.
Of course, being careful will prevent contaminants from entering the hydraulic system, but it’s very important to be very careful, otherwise the fluid could be compromised.
If the environment that you keep your hydraulic system in is far from clean and dry, then you may prefer to use a sampling kit. It cuts down on the potential for contaminating the hydraulic fluid. It is not funny when you go out of your way to ensure that everything will be ok, but then realise that something must have gone wrong when you find a large particle in the system.
The sampling system is inserted into the access plug that the pump came with. Once the plug is in place, then I won’t protrude more than 1 inch, which makes it a very easy system for those who are limited to smaller space.
Then once the tap is in place, it’s easy to just unscrew the cap which will expose a cavity where you can easily take a sample from. There is then a sampling probe which will connect to the sampling valve. You’ll then find a length of clean sampling tube that connects to the vacuum pump and a clean sample bottle. Just pull on the handle to draw out fluid for adding to the sample bottle.
Taking clean samples is essential in order to take a balanced view of what’s going on with any hydraulic system. It’s possible to attain this by using one of the sampling valves that are available on the market. They create a closed loop circuit which will prevent any contamination from entering the oil sample. The sample can only be taken once the probe is fully engaged with the valve. Once the sampling probe is disconnected the sampling valve will reset.
By taking clean samples, you can discover what is going awry with your hydraulic system, and even predict potential future issues. However, if it’s not clean or you introduce further outside dirt or muck, then it’s not going to be at all helpful and you’d be better off not doing it at all. Ensure that you keep your sampling clean to promote the ‘health’ of your hydraulic system.
Hydraulic Power Pack
Connect with us
Connect with us on social media or eBay