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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.
Cavitation was first discovered in 1917 when Lord Rayleigh (a British physicist) decided to investigate why fast-rotating ship propellers were eroding at such an incredibly rapid pace. He discovered that it was all down to a condition that came to be known as cavitation.
Cavitation is related to the word, cavity and has the Latin verb ‘cavitere’ at its root. It means to ‘hollow out’ and that’s exactly what cavitation does. Cavitation occurs when very hot small air and gas bubbles develop. As they reach high pressure areas they collapse and cause hot jets to hit the surface of any pipe or components that is reachable causing erosion.
When liquid passes through an hydraulic valve, it is under pressure due to the size of the valve. The speed of the flow will rise and then the speed drops again. This change in pressure will create a vapour and then small bubbles of gas will form. When the pressure gets higher than that of the vapour, the bubbles will collapse as the vapour liquefies again. The bubble collapse can send out the heated fluid jets which are very powerful and it’s this that causes so much damage to metal.
Cavitation is no joke. It can be so severe that it can completely destroy hydraulic valves, pumps and piping to such a degree that the entire system can fail. In between, you may need to contend with leaking valves or even holes in pressure vessel walls.
Even cavitation that is at a low level can wreak havoc by eroding components until they need to be replaced. This is how engineers can recognise that their system is suffering from the effects of cavitation:
· Banging or knocking noise
· Chocked flow
· Fluid property changes
· Valve component erosion
· Control valve destruction
· Failure of plant leading to shutdown
Cavitation damage can often be identified visually with the use of either a microscope or a magnifying glass. If you are wary that cavitation is causing damage to your hydraulic system, check whether or not it is general wear and tear through corrosion. Some types of corrosion will actually mimic what you’d experience through cavitation. You can expect to find cavitation damage, if it’s in existence, downstream of the seating areas for the control valve. You could very occasionally witness cavitation bubbles further downstream from there.
Another easier way to identify whether your system is suffering from cavitation damage is to listen out for the noise of either crackling or popping. As pressure drop occurs, the cavitation will ramp up and you’ll hear rattling or hissing that increases in volume. If the cavitation is in full operation, it will sound more like you have a lot of small rocks or gravel passing through your system.
Cavitation is so powerful that there is currently no known material that can stay undamaged by it. The only way to deal with it is to eliminate it.
One of the simplest ways to eliminate cavitation is to reduce the operating temperature within the hydraulic system. The vapour pressure will be eliminated. If you have identified a valve that is experiencing cavitation, when you replace it, try to install it at the lowest possible elevation within your pipe system.
Another possible solution to cavitation issues is to introduce air or nitrogen into the area of the system where you are expecting to get it. It will need to be added through either the valve shaft or through a tap downstream on aside of the pipe as close as possible to the valve.
If for some reason you are unable to change the process conditions, then it’s recommended that you use valves with low recovery and treacherous flow path as opposed to high recovery valves such as the gate, ball or butterfly types.
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.
Made of a number of precision machined components, hydraulic equipment and systems require care and maintenance to get the best of them and in order to give them what they need for long lasting and trouble-free operation.
We’ve covered troubleshooting before, and if you want to know more in further detail then check out our blog posts on:
Troubleshoot Hydraulics: Basic Knowledge
Troubleshooting Hydraulic Relief Valves
This checklist is for those who have not had extensive experience with troubleshooting hydraulics and it might suit your interns or newbies in the workshop.
Let’s get started.
First off, it’s essential to keep all of the hydraulic system clean. This includes the hydraulic fluid. Oil and oil filters need to be changed at regular intervals. You could say that dirt and grime is your and your equipment’s worst enemy and it’s your role to keep it at bay and prevent it from messing up your machinery and its peripherals.
Here is a checklist of what is at the root of most trouble:
1. The fluid or oil being used is not of the correct viscosity.
2. There is not enough fluid or oil in the system
3. There is a leak
4. There is dirt, moisture or there is another foreign body in the system
5. There is air in the system
6. Structural failure.
7. Adjustments have been made but they are wrong
Here are some shortcuts to answers that you can refer to when getting started with hydraulic troubleshooting:
Your Pump is Operating Incorrectly and not delivering fluid or oil. It could be down to any of these reasons:
· The fluid is too low in the reservoir. You may need to check its level and refill if necessary.
· If there is a hole in your intake pipe allowing air to pass through, you may hear a noise or experience erratic results. This will need to be repaired. Alternatively there could be a blockage in your filter. In which case, you will need to clean it.
· The oil is too thick and the viscosity is too heavy. Check the specs suggested by the manufacturer.
· The pump shaft is rotating in the wrong direction. Reverse it otherwise you will cause irreparable damage as there won’t be enough lubricant.
· Dirt in the pump – clean it.
Your System is Not Developing Pressure
The most likely causes for this type of situation are:
· The pump is not delivering fluid (see info above – with remedies listed)
· The relief valve is malfunctioning either through leakage, incorrect settings or because the valve spring is broken. You may need to check the settings according to the manufacturer, check the valve seat to look for either dirt or scoring or even replace the spring and then adjust it as suitable.
· The valves may be allowing the oil to be recirculated through the system. Check the directional valve to ascertain what the situation is with it.
· There is leakage internally in the valves or the cylinders. Check these components and their condition.
Pump is making noise
· The intake line or the filter is not allowing fluid to pass. Clean these and assure there are no kinks or anything to stop them being fully open.
· There are air leaks either in the intake pipe at the joints, at the pump shaft packing or through the inlet pipe opening. You can check the joints for leaks by pouring on oil. Also check the shaft by pouring oil onto it and check that the inlet pipes are below the oil level in the reservoir to ensure that suction is strong enough.
· If you are seeing air bubbles, you may need to use an oil with a foam depressant.
· Check the reservoir air vent to see if it’s plugged, if so clean it.
· You may find that the pump is running too fast, in which case you will need to refer to the manufacturer’s specifications.
· The oil is at the wrong viscosity. Again, check the manufacturer’s specifications for details.
· Check whether the filter is of the correct size, as this could also be a problem. Refer to manufacturer’s specs for details.
· Check for work or broken components and parts, and replace as necessary.
If you’re experiencing an external oil leak around the pump, you may need to look for:
· Worn shaft packing which needs replacing
· Head packing damaged, again replace it.
· Loose or broken parts, which may need to be tightened or replaced.
Excessive wear can be caused by and remedied as follows:
· Abrasive material or dirt in oil being circulated. Clean and/or replace the filter and change the oil.
· If the viscosity of the oil is too low, check what is recommended by the manufacturers.
· Pressure could be too high for maximum rating of the pump. In which case you may need to check the settings of the relief valve or regulator valve.
· The drive is not aligned correctly. Check this and correct as appropriately.
· Air is in the system. This will need to be removed.
Broken pump parts can come about from:
· Pressures are above the maximum pump rating check the relief or regulator valve settings.
· Seizure from lack of oil in the system. Check the level of the reservoir, the oil filter and the suction line.
· Dirt or material in the pump – clean it and check the filter.
· The head is screwed on too tight – check the specifications as listed by the manufacturer.
Follow our blog for more handy hydraulic system troubleshooting checklists.
Checklist for Hydraulic Power Troubleshooting
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.
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.
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