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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.
Changing the filter element in your hydraulic machinery is a very important part of routine maintenance and for this reason it is often tacked onto a schedule and done at a set time, usually determined by the number of hours it has been in service for. Changing filter elements, wherever they are situated in the hydraulic loop, needs to be done in order to keep the fluid as clean as possible to therefore prolong the life of the components in the system, however, getting the timing right to ensure you are making the most of your expensive filter elements is a more intricate art than simply totting up the service hours and basing a filter change schedule on that data alone.
If a filter element is changed early it will still have plenty of dirt holding capacity left, and to replace one with life left in it is a false economy – yes, you will not run the risk of leaving it too late and potentially allowing contaminants into the oil, but it is also a waste of resources. Leaving an element change too late means that dirt can enter the system and cause damage to the components, leading to machine failure and spiralling associated repair costs. If we cannot use service hours to inform the timing of a filter change, how can we tell when is the right time for a switch?
The location of the filter can make a difference to the regularity of the element changes, as pressure filtration systems work a lot harder than off line or return filter systems. They are often higher in initial cost as well as in ongoing maintenance costs, but offer a fine level of cleansing as they can trap the smallest particles, thanks to the pressure forcing the fluid through the filter. The same pressure can dislodge trapped dirt, sending it back into the machinery and causing damage, so there are also downsides to using this location for hydraulic fluid filtration. Off line filtration systems are also very expensive but are the most effective at filtering, as they run continuously and therefore offer the best extension of machinery life. They also require regular replacement of the filter elements, as they are active for much longer than a filter that is only operational while the machinery is running. Return filtration is the most popular and most economical location for filtering hydraulic fluid within a system and also offers the opportunity to filter new oil in via the same part of the loop.
The best way of knowing when a filter element needs to be changed is to monitor the pressure drop across the filter, with a marked drop in pressure on the downstream side indicating that the dirt holding capacity is almost used up. A clogging indicator is one way of measuring the pressure drop and this can be used when it is suspected that the time may be approaching. Clogging indicators can be visual or electronic and set to go off before the pressure for the filter bypass valve is reached. Not all hydraulic systems have a filter bypass, but those that do can link the associated pressure point to the point at which a clogging indicator is activated.
A more sophisticated system involves continually monitoring the pressure drop across the filter, wherever it is located, and the resulting data can be used to inform a more reasonable and reliable filter element change schedule, as it shows the true lifespan of the filter elements. The data also acts as an early warning system of system or component failure. Although an advance continuous monitoring system costs more, in the long run it will save money on unnecessary filter changes, warn of expensive system failure before it happens and provide valuable information about the operating capacity of your hydraulic equipment that could prove a lot more valuable in the long run, and just think - all these benefits can arise from simply trying to work out a proper filter element replacement schedule!
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.
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.
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.
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.
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