MACHINE safety is no new concern for manufacturers, but according to Fluidsentry director, Murray Hodges, only recently have safety devices specifically designed for fixed hydraulics equipment been made available.
“For a number of years we’ve had light curtains and programmable safety systems, safety relays and lift monitors, gates and guards and emergency stops. You can buy those products anywhere, but on the actual fluid power valving, there hasn’t been a lot available,” he told Manufacturers’ Monthly.
Traditional safety measures for fixed hydraulics systems relied on cutting power to the coils. Hodges says failures and accidents have occurred using this method due to electrical faults, energy stored upstream and general wear and tear.
He claims new products such as cartridge valve systems are helping make fixed hydraulics safer.
A cartridge valve systems has two valves and multiple drains. “It’s what we call a block and bleed system, so we actually shut the system or the hydraulic flow off and then bleed off all the stored pressure in the lines.”
Valves are connected in series to provide redundancy in case either should fail. Valve components are monitored, and the system is said to immediately detected failures and prevent operators entering the machine.
Hodges warns not all monitoring devices are equally effective. “One of the big problems I’m seeing out there is the use of inductive proximities on valving,” he said.
Inductive proximity switches have a set field of measurement and Hodges claims unless the device is positioned with a high degree of accuracy, fluid may flow through the valve undetected. He added the devices’ failure modes may also be difficult to determine and mechanical switches such as those used to monitor cartridge valve systems tend to be more reliable for safety applications.
According to Hodges, different load types would also require different safety mechanisms. With gravity loads for example, valves can be shut but the system’s strength then depends on the strength of the flexible hoses. “If the flexible hose between the valving bursts, the load can come crashing down,” Hodges said.
One possible solution Hodges suggests is using additional monitored valving between the two main valves to further fail-safe the system.
He says such valves are currently available, but without monitoring. “So if they do fail, no one could possibly know…we’re looking at doing a monitored device,” Hodges said.
Mobile Hydraulics
Sauer-Danfoss managing director, Lance Thomas told Manufacturers’ Monthly safety has always been a major focus for mobile hydraulics, and advances in electronic controls are making equipment such as skid steer loaders even safer and easier to use.
Skid steer loaders are traditionally difficult for inexperienced operators to handle, but Thomas claims new controls and closed loop applications help minimise the difficulty.
“In the past it was very dangerous for someone to [hire a loader] because without the experience, they could get hurt. That’s not to say that you can put inexperienced operators on these machine, but it’s just to say that some of the special idiosyncrasies of the machines can be ironed out so that the operator won’t take so long to become familiar with that machine,” he said.
According to Thomas, electronic controls are also being used for measuring and manipulating operating parameters. He claims this also makes machines easier to use, and can lead to productivity gains as the machine automatically determines the most efficient combination of parameters.
Hydraulic components used in mobile equipment have also become more efficient over the past decade, Thomas says. Product designs have changed improving efficiency from around 70% to between 90 and 95% in many cases.
Thomas says while efficiency will continue to improve, moving above 95% efficiency may not be cost effective. Rather, Thomas expects quality and power to weight ratios to improve, components to become more compact, and controls to become more user friendly.
In the long term, however, Thomas sees electric control taking over some areas previously dominated by hydraulics. “There are areas such as forklift steering which were traditionally the domain of fluid power, hydraulic steering. These areas now are being targetted by small dc or ac electric motors through gearboxes,” he said.
“Unless there is a change in focus, that we have more OEM manufacturing in Australia, the fluid power industry is going to end up being purely an end user market place, a service market place and that is a concern,” Thomas said.