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Launch and Recovery System (LARS)
What is it?
The “A” Frame section is moved from the inboard stowed position to the outboard launch position by Hydraulic Luffing Cylinders. The hydraulic luffing cylinders are controlled and operated from a central control point on the “A” Frame base, where all the individual proportional control valves are located, including the controls for winches.
The individual proportional control valves where applicable are fitted with internal motor spools which give excellent control during operation of the winches.
The hydraulic cylinders are fitted with fail safe load holding counterbalance valves, to protect against hydraulic pressure failure during operation. The pivot points on the “A” Frame assembly are fitted with Stainless Steel grease nipples for lubrication purposes.
An electrical top limit switch is installed adjacent to the central fixed sheave which will trip the HPU in the event the dive basket is raised above its normal operating parameter. This additional safety feature protects the basket occupants and equipment.
At Hydraproducts we have incorporated further safety features on our HPU's with redundancy systems, this will ensure the safety of divers and valuable equipment if the hydraulic unit should ever fail.
Hydraproducts has a wealth of experience in supply and manufacture of bespoke Subsea Marine Hydraulic equipment. We specialize in bespoke projects with emphasis on quality and delivery.
For those seeking to upgrade HPU equipment in order to gain cross-compatibility with different systems, or to improve the systems performance with current equipment, Hydraproducts can provide the necessary expertise to all corners of the world.
For more information on Subsea Hydraulic products please contact the main office.
If you’re a hydraulic power engineer and you follow our blog posts, we are now going to take you on a journey deeper into our niche and introduce you to one of our hydraulic power unit related specialist areas, known as LARS or Launch and Recovery Systems.
To understand what’s involved in these machines that are used offshore in marine environments such as on oil rigs, we need to get familiar with the individual components:
Every launch and recovery system is equipped with an umbilical winch. This has to be able to accommodate the entire length and diameter of the remotely operated vehicle umbilical. This winch will typically make use of a level wind mechanism to cater for even spooling of the umbilical cable on to the drum of the winch.
To power the winch there is usually a suitably sized hydraulic winch motor attached that can pull in the remotely operated vehicle (ROV). This is where the hydraulic power pack comes in to play.
A Crane or ‘A’ Frame will need to be able to lift and on-board the ROV. It will also need to be strong enough to be able to accommodate the weight of the vehicle plus its load.
Most often it’s easier to put the ‘A’ frames and the hydraulic power unit HPU together on a dedicated mounting skid base so that they can be easily welded to the deck. Although they are sometimes positioned to be stand-alone units.
It’s a requirement for the LARS to be certified for use. This will generally include a Lloyds witness of the system load tests or DNV design approval. These are required prior to manufacturing. They are something that can cause delay and is most often extra cost.
A bit of a crash course into the world of LARS. We will be featuring more about this fascinating area in our blog posts, so if you’re unfamiliar with the offshore industries, you will have a chance to find out more about them and how we apply our hydraulic power packs in this field.
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.
Humans are creatures of habit, we like routine and familiarity as it makes us feel safe. Change is a hard pill to swallow; although some people deal with it better than others it can take a lot for someone to proactively look at a different way of doing things. Change is usually something that is imposed upon a person out of necessity, so if there is no perceived reason to change a situation then we generally carry on as normal.
This thought pattern may be one reason why hydraulic systems designers tend to opt for high pressure systems and the familiar components that can cope with being under extreme pressure. It is far easier to take an existing basic idea and tailor it for a new application without even considering alternative approaches, which is why low pressure hydraulic systems are something of a rarity in the world of fluid power.
The basic equation of force = pressure x area, lends itself to working with a smaller area and a higher pressure to exact the same amount of force that a large area under lower pressure would exert. This is attractive to designers as it means systems can have sleek, narrow cylinders and in many cases, this is needed to ensure the assembly fits in the space available. That is not always the case, however, so hydraulic designers should consider low pressure systems as a possibility for some applications.
Low pressure hydraulic systems can be a lot more cost effective than high pressure ones, as there is a reduce possibility of leaks, and if they do occur they will take less time to clean up and fix. The materials used to build the components can also be a lot cheaper, as they will not have to withstand the high pressures normally associated with hydraulic systems. Plastic components, flexible nylon tubing and even thin extruded aluminium cylinders all work perfectly well at pressures under 50 or 60 bar, and are a lot more economical than the high pressure alternatives.
Sometimes a low-pressure system is really the only possible solution to a problem, especially when designing complex systems with many lengths of tubing, serving several small cylinders off a central motor. This is when the materials that need to be used dictate the operating pressure of the system, rather than the operating pressure dictating the materials. If the pipes need to fit through pre-defined holes in the machinery casing, or need to wind around parts of the machinery then flexible nylon is the best option. This low-pressure approach allows designers to consider every angle from which to solve the design problem, and can result in some great innovations that otherwise might have gone undiscovered.
The only drawback to low pressure hydraulic systems is the need for a larger reservoir to hold the extra fluid that is needed to fill the system when it is in operation. Size and space can be a stumbling block for low pressure systems, as the larger cylinder diameter means more space is needed. Sometimes this can be cleverly engineered in, by placing the reservoir further away from the operational components of the hydraulic system and making good use of the cheap nylon tubing to run the fluid up to the moving parts.
There will always be cases where high pressure systems are a must, due to the application, the forces needed and the space available to house the hydraulic system, but at the same time there will always be systems where low pressure is more effective in terms of performance and cost, so considering both angles before diving in to a design is a worthwhile task that could lead to the next big thing in hydraulics.
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.
When replacing hydraulic fluid, it is tempting to believe that the new oil will be clean and free of contaminants, and that it can be put straight into the reservoir without any problems. Unfortunately, this is not always the case. If you use hydraulic oil from a large drum, there is a high chance that it already contains some water and dirt particles; new hydraulic oil typically has a cleanliness level of ISO 4406 23/21/18, which is more than most hydraulic systems will tolerate. If the system has a rating of say, 20/18/15, then the new hydraulic oil is already too contaminated, as a single digit increase in any of those numbers is effectively a doubling of the contamination level for each micron size.
We can see, therefore, that it is a good idea to filter new hydraulic oil before it enters the system taking with it contamination that will potentially lead to problems with the system. Most hydraulic system failures can be traced back to contaminants in the oil causing friction, high temperatures and a loss or build-up of pressure that can cause serious damage to the components within. Avoidable problems should not be encouraged by cutting corners when replacing hydraulic fluid as it is a false economy.
If you usually replace the hydraulic oil straight into the reservoir, you can add a filtration cart or a kidney loop system to clean the fluid before it gets into the system itself. Even if you have a filter downstream it is a good idea to still keep a filtration system in the reservoir too, to ensure that the downstream filter does not have to work too hard and retains the lifespan it is expected to have, cutting down on element changes. A kidney loop system is ideal for filtering hydraulic fluid in the reservoir and runs independently of the equipment itself, meaning it can still be cleaning the oil even when the equipment is not being used. This means that the fluid can be filtered thoroughly before the machinery is switched back on and also offers a higher level of filtration throughout the life of both the hydraulic fluid and the equipment itself.
Dual filter elements are usually used in kidney loop systems to filter out particles of different sizes and ensure that the filter does not become clogged too early. This also allows for better element change schedules as they can both be done at the same time, rather than replacing the first, then the second, then the first again and so forth more frequently. The dual filter elements in a kidney loop system also perform better than in-system filters, as they are not exposed to any pressure and can retain contaminants more effectively.
Alternatively, new hydraulic fluid can be filtered into the system via the return filter. If the application is very sensitive, it may be best to stick with a kidney loop filter, but if this is not possible due to the nature of the hydraulic equipment, the return filter route is a good option. A tee needs to be installed in the return line above the filter, and one branch connected to a drum pump discharge hose via a quick connector. When it is time to filter the new oil in the drum pump, it is attached to the return line and the oil gets pumped through the return filter and into the reservoir.
Not filtering new hydraulic oil into a system basically opens the door wide to dirt and water getting in, and undermines maintenance activities and careful user behaviour designed to keep the equipment in full running order. If you need to change how you replace the hydraulic fluid or add a filtration component into the system, the cost of doing so should be weighed against the savings in unnecessary maintenance and repairs due to contamination related damage.
System performance and longevity can be greatly affected by using different viscous fluids as well as the various individual system components that can suffer reduced lifespans and early failures if the wrong fluid is used.
The size and also the structure of molecule chains are the crucial factors in measuring a fluids viscosity and the larger the molecules, the thicker the fluid.
To get around this hurdle, multi-grade fluids are used which typically have a high viscosity index and are less sensitive to temperate change than a typical monograde oil.
As lubrication is the prime objective of hydraulic fluid, it is essential that full lubrication is maintained even if temperatures fluctuate. If this does not happen, boundary lubrication is witnessed which means that only a thin layer of fluid works with system componentry, thus leading to possible friction issues and component wear.
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