Mechanical Technology October 2015

⎪ Hydraulic and pneumatic systems ⎪

the vehicles’ functions. A particularly sophisticated hydraulic system is used to handle the opening, closing and clamp- ing of the tank door. “These vehicles are emptied like tipper trucks. The back door opens and a hydraulic ram raises the cab end to discharge the tank’s contents through the door at the back. But in op- eration, the tank needs to be well sealed to hold the vacuum. We use six hydraulic clamps around the rear door seal. Each of these each has an interlock and a hy- draulic cylinder for opening and closing the clamp mechanism. And when open, hydraulically actuated hooks secure the door to allow people to safely enter the tank to clean it,” Visser says. The clamping and interlocking system is operated via a hydraulic sequencing circuit that uses a manifold block with Sun Hydraulics cartridge valves. “We use kick-down valves, which deliver a pressure spike as a circuit is completed. By designing the system to produce spikes at the appropriate pressures, we achieve a very robust cascade activation sequence,” he explains. “The clamps open in the first hydrau- lic sequence. Then the door opens and, finally, the safety lock engages – and the sequence control is 100% mechanical. We do not depend on any electronic controllers.” The system also has an equivalent reverse sequence to close the door again, with the lock releasing, the door closing and the clamps re-engaging. This is achieved via a separate hydraulic circuit built into the same manifold block. “Both sequences are fully automatic, so an operator cannot close the door while the lock is still engaged, for example, which would damage the mechanisms. “Sun Hydraulics cartridge valves are so accurate that you can activate them during a half cycle. If the door is half open, the system can be put into reverse, which will close the door safely in the reverse sequence. Nothing needs to be reset. The sequence simply trig- gers immediately on activation,” he tells MechTech . Highlighting the advantages of using hydraulic controls, Visser relates that the Highpoint HPVR 1000s typically work at acid plants and in petrochemical compa- nies, which are highly corrosive environ- ments. “Exposed electrical connections in these environments will corrode, making the vehicle unreliable. “The nice thing about hydraulic con-

filters, for example, a little moisture will trigger the reaction to set the cement and destroy the filter. This has really happened! That is why we have the elec- tronic monitoring system fitted, to protect the truck from costly damage,” he says. HPVR Combis Designed for combined jetting and vacuum applications, such as municipal sewer and line cleaning, Highpoint’s Vacuum trucks can also be used for vacuum applications such as emptying industrial sumps and slurries, removing toxic waste, and wet and dry ash removal from power station boilers. “In the rainy season, a lot of mud and silt accumulates in the drains, which cannot be carried away by subsequent liquid flows. To clean this from the drain, we use a retrojet nozzle, which has more jets pointing backwards that forwards,” Visser explains. Typically, this nozzle is fitted to the end of a 120 m sewer cleaning hose on a hydraulically driven hose reel behind the truck. “This jetting nozzle is placed down a manhole into the drain line. Water is pumped through the nozzle at about 200 bar and, because there are more jets pointing backwards than forwards, a net forward thrust is generated. This propels the jet and hose up the drain towards the next manhole. “Once there, the hydraulic reel is acti- vated to withdraw the hose, causing any sediment to be washed down towards the entry point, where a separate vacuum tube sucks the waste and water back up into the truck, allowing it to be safely disposed of at an appropriate dump or sewage plant,” Visser says. When using a traditional Combi truck, according to Visser, the operator might spend a third of each day looking for water from fire hydrants, for example, refilling and returning to the manholes. Overcoming this problem is the com- pany’s recently released Recycler, which, in addition to all of the features of its traditional Combi trucks, also includes an onboard system to filter the water from the waste so that it can be reused for jetting. “The water recycling system itself is sourced from Dietmar Kaiser, but all of the rest is built here in our facility just outside of Sasolburg,” he adds. The hydraulic door clamping system All Highpoint vehicles contain a range of hydraulic pumps and circuits to support

The vehicle and equipment arm of Highpoint Vacuum now has a production capacity of more than 20 vehicles per year.

trols is that the whole system is hermeti- cally sealed and 100% protected from outside influences. Everything is running in very clean oil, which makes it ideal for use in dirty, corrosive and aggressive environments. We also use hydraulics for most of the physical actuation tasks, such as the tank tipping and aligning the hose reels, with pneumatic actuators for the valves. But we try to stay away from PLCs as much as possible on the industrial vehicles,” he says. “When we have to use electronic controllers, for municipal vehicles, for example, we use IFM-controllers, a German specialist in mobile electronics that manufactures 100% sealed IP65- rated, so they are not prone to dust or moisture ingress,” he adds. “Like-for-like, our vehicles are about 20 to 30 % cheaper that imported equivalents. Compared to our European competitor, our trucks are at least R1.5- million cheaper and, more importantly, our turnaround times are much better. If ordering from Europe, first, you are forced to use a MAN truck, which is already about R400 000 more expensive than the UDs we use, and we can deliver in four months, from order to delivery. In addition, we can offer unparalleled turnaround times on spares and repair,” Visser concludes. q

Mechanical Technology — October 2015

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