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Hybrid valve design offers lower cost, longer life
Combines hydraulic power with electric actuation
By Design News Staff -- Design News, March 4, 2005
Using a hybrid design that combines hydraulic power with electric actuation, a new valve could deliver cost-effective servo-like performance in applications ranging from conveyor drives to mobile equipment accessories.
Known as the F24 motorized flow control valve, the device combines a flow rate of 130 gallons per minute (gpm) with the ability to offer infinite valve adjustments ranging from fully closed to fully open.
“It can be a very inexpensive, bullet-proof way for bringing remote electronic control to high flow rate applications,” notes Gary Miller, president of Source Fluid Power (Chaska, MN), maker of the new valve. “If someone is controlling a big piece of mobile equipment, and wants to adjust the speed on an application, they can easily do it through this valve.” Miller said that in addition to mobile equipment applications, the valve can serve in grinders, fan drives, and process pump drives.
The key to the new system is its use of a brushless DC motor, planetary gear set, and microcontroller to rotate a spool on the valve, thus providing an infinitely variable range of valve openings. By doing so, the valve can achieve a high level of flow control, while using as little as 24 W to actuate the spool. At the same time, it does so for far less cost than traditional servos and proportional valves. Source Fluid Power engineers say that their 130-gpm valve costs between $1,000 to $1,500, while servos typically run from $2,500 to $5,000 and proportional valves go from $2,000 to $2,400.
The company’s engineers acknowledge that the product serves a precisely-defined niche, and can’t be used in certain control applications, particularly calling for very fast response times. While servos typically have response times of 100 milliseconds (msec) or less, Source Fluid Power’s cartridge-type valves go from full-open to full-closed in about one second.
“If you’re controlling a machine that needs really fast performance, this is not the right valve,” notes Pat Novak, an engineer and sales manager for the company. “But in any application where you want to control the speed of a high-flow hydraulic motor or cylinder, this valve can do it.”
The F24 valve uses a brushless DC motor to rotate its spool, thereby offering infinitely variable valve adjustments.
Novak says that the company developed the technology during the 1990s, but applied it to smaller valves with lower flow rates, typically not exceeding 50 gpm. But by changing to a larger cartridge size and using a brushless DC motor, instead of a brush-type motor, the company vastly increased the flow rate and achieved the added benefits of longer life. The F24 reportedly offers an estimated life of 2.5 to 3 million cycles, which is significantly more than could be achieved by a brush-type motor, or a servo or proportional valve.
The company also claims that its technology offers a softer shift than faster-acting proportional and servo valves.
“If you shift 130 gallons per minute in 50 milliseconds, you run the risk of getting ‘water hammer,’” Novak says.
Source Fluid Power engineers say they were prompted to design the new valve by customers who wanted variable control of a high-flow-rate valve, but needed to combine that control with soft shifting and longer cycle life. Those customers said they were unable to attain two to three million cycles with a conventional servo valve.
The company plans to target the valve at conveyor drives on manure spreaders and asphalt pavers, as well as on sewer cleaning trucks and harvesters. Using the new valve, OEM engineers could enable operators to control accessory speeds simply by toggling a switch, thus changing the opening on the valve.
“All of those applications offer potential because they don’t really need 50-millisecond response times,” Novaks says. “They just need a simple way to adjust the valve.”
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