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Closed-loop hydrostatic drive proves an efficient muck shifter!

21 November 2012

Green Cove Springs, Florida based Vac-Con is one of the USA’s largest manufacturers of drain cleaning equipment, and its Combination Cleaning Machines are the most popular products. These combine a high-pressure water jet pipe cleaning system with a vacuum system to remove accumulations from sewers and storm drains.

Aware that innovation was going to be the key to its continuing success, the company was delighted when it was invited to join Eaton’s pump development programme. As a result of joining the programme, Vac-Con has since adopted Eaton’s new 760 series hydrostatic pump as standard equipment on its storm water drain cleaning vehicles This replaces another manufacturer’s pump that it had been using for 17 years. Vac-Con engineering manager, Tom Armstrong takes up the story:

“The 760 was part of the pump development programme and we field tested it over 18 months of real-world use. It proved to be a viable product and better than anything competitively available. But it was a prototype, so we continued to specify the original product.”

However, three years later when Vac-Con was temporarily unable to get pumps from its usual supplier. the company renewed its contact with Eaton. The 760 pump wasn’t a production item then, but Eaton and the local distributor, Jacksonville based Hydraulic Supply Company, pulled out all the stops and delivered the first production pumps in short order. “…..and they’ve been arriving on time ever since,” adds Mr Armstrong. “We had to be galvanised into making the switch to Eaton’s 760, but I am glad we did.”

Vac-Con’s waterjet cleaning system operates at 140-200bar with flows of 2-7.5 litre/s, to clean land drains up to 300m long. The vacuum system lifts accumulated debris out of the catch basin and into a truck-mounted collection tank.

Both the high-pressure water pump and Vac-Con’s high performance fan (the only fan in the industry that can vacuum underwater) or positive displacement blower for the vacuum system are powered by engine-driven Eaton 760 hydrostatic pumps. Vac-Con introduced the concept of a closed-loop hydrostatic drive system to the industry to eliminate the inefficient, maintenance-prone mechanical drives that are still used on many competitive products. Tom Armstrong again:

“The hydrostatic drive delivers smooth, infinitely variable power. The pumps and motors are connected in a closed loop, and we inject cooling oil with an auxiliary charge pump on the low pressure side to control system temperature. It’s a very efficient and reliable system.

“We have a lot of experience with hydrostatic drives, so we didn’t expect any surprises when we swapped to the 760 pump. But, when we installed the production pump we discovered that the Eaton controller with its ability to customise stroking speeds brings the pump on stroke at such a controlled rate that it virtually eliminated an engine ‘bogging’ problem that had challenged us for many years.

“The 760 is so smooth we can use the full 130cc stroking volume right from the start. With the old pump we had to de-stroke and run at a higher rpm to pick up the fan load. This has had a very positive impact on fuel economy, and that’s a huge issue today.”

Integrated Valve System
The Series 760 features a new design concept for Eaton Hydrostatic pumps called the Integrated Valve System (IVS) that combines a high-pressure relief valve, a pressure override control (POC), system check valves, and a bypass valve in one cartridge. By combining these functions in a single cartridge, the IVS reduces pump size and weight while simplifying diagnostics, troubleshooting, and service.

The direct acting high-pressure relief valve actuates whenever system pressure equals the relief valve setting to protect system components from pressure spikes. The POC works in combination with the high-pressure relief valve to protect the transmission when it is operated for extended periods at overload pressures. If the system pressure reaches a preset limit, the pump de-strokes and adjusts its displacement to the load.

Eaton engineers also modified the housing and valve plate on the 760 series to make them stronger and quieter. 

“I’ve recommended the 760 and other Eaton products to several of my associates who use hydrostatic pumps. That’s not something I would do if I had any doubts about their willingness and ability to deliver what they say they will, when they say they will,” says Armstrong.

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