New Valves For Hydrostatic Fan Drives, Directional Control

Diesel Progress North American Edition, July, 2001

While a lot has changed at Hydraforce over the years -- the company has moved operations, facilities have been built and expanded, etc. -- one thing has remained constant throughout. No matter what else has been going on, HydraForce has been extremely active in developing and introducing new products.

Most recently, the company has developed a series of new valve products for mobile equipment applications. These include the TS-27 proportional relief valves designed for hydrostatic engine fan drive systems; the SP series valves, used for speed and directional control of hydraulic cylinders and motors in mobile equipment applications; the SV120-60 selector valve and SV98-T39 flange-mounted solenoid; and 08 size miniature proportional flow control valves.

The TS-27 valves provide variable control of fan motor torque and/or speed and are appropriate for fan drive systems in both on-highway trucks and buses as well as off-road equipment. Electronically controlled hydrostatic fan drives are gaining an increasingly large following in equipment circles. Advantages include more precise control of coolant temperature through control and modulation of fan speed, as well as a high degree of packaging flexibility, since the systems are not driven directly off the engine.

Other benefits include reduced noise generation -- the fan only runs as fast as it needs to in order to provide the proper level of cooling -- which also can provide significant energy savings.

In most systems, the temperature of the engine coolant is controlled with an axial or radial fan, which is driven by a hydraulic motor. Oil flow to the motor is generated by an engine driven fixed displacement pump. The motor is controlled through a relief valve, such as the TS-27, which is positioned in the bypass leg of the fan drive circuit. Maximum fan speed is achieved when the proportional relief valve is at its highest setting.

The TS-27 valves are available in a range of sizes to fit requirements of the specific fan drive system. "It's a family of products," said Richard Fontecchio, HydraForce's vice president, marketing. "We can provide everything from a little pilot cartridge to a 12 size and ultimately, the pilot cartridge could pilot logic elements for even higher horsepower hydraulic fan drive packages.

"It's a big growth market," he added. "There are a couple of things driving it, but certainly efficiencies are an issue.

The TS-27 valves are normally closed with no electric current applied, and ramp open to decrease pressure when increasing current is applied, providing the proportional control feature. Control range is firm 2000 psi to near zero with input current of 1.2 amps at 12 Vd.c.

The valves fit industry-common cartridge cavities and feature HydraForce's wet armature linear solenoid. The newest model in the line, the TS08-27 can accommodate input flows up to 5 gpm.

"One of the neat things is that they electrically fail to the closed position," notes Fontecchio. "It's the reverse of most proportional valves where you would increase the current and increase the pressure. In this case you increase the current and decrease the pressure, so they fail the right way."

The new SP series valves provide proportional speed and directional control for hydraulic cylinders and motors. The four-way, three-postion units are designed for functions such as drive control on scissors lifts, control of small truck-mounted cranes, lifting of mower decks on turf equipment and similar mobile equipment applications where precise control is required.

The new valves are available in both closed-center and motor-spool configurations. The 08 size is rated for flows up to 3 gpm, while the 10 size is rated for flows up to 6 gpm. Both sizes can operate at pressures to 3500 psi and are available with 12 or 24 V solenoid coils with various connector options. An electronic controller for the SP series valves is also available, the company said.

The new SVl2-60 solenoid-operated, 12-size, six-way selector valve is rated for flows to 15 gpm in selector circuits and flows to 8 gpm in series/parallel drive circuits at pressures up to 3500 psi, It is a screw-in cartridge valve that can be included in an integrated hydraulic manifold consisting of other cartridge valves and control functions. Installation time, external plumbing and space requirements are minimized, HydraForce said.

The SV12-60's extra heavy-duty d.c. coil meets or exceeds all 1P67 standards for thermal shock, weather resistance and "dunk capability" under the most demanding application conditions, according to the company The coil features a rugged, external metal shell surrounding a seamless, completely encapsulated coil winding.

As a selector valve, the SV12-60 is well suited for function selection applications on construction, agricultural and material handling equipment requiring support-tool and auxiliary operations on boom-end, masts, or hydraulic PTO ports. As a series/parallel drive selector, it can be used on scissors lifts and other construction equipment, the company said.