New ZL Series proportional flow control valves from HydraForce Inc. (Lincolnshire, IL) are internally pressure-compensated and operate in two directions. "The valves provide identical flow vs current characteristics in opposite directions," says Zilek Lieberfarb, the inventor of the valves and an engineer at HydraForce Inc. "This allows use of one proportional valve instead of two," he says.

With no change in hysteresis between the forward and reverse flow directions, the valves eliminate the need for separate circuits in many hydraulic control applications, including off-highway and construction equipment where controlling the speed of operation is performed with single- or double-acting cylinders. "These valves have built-in compensators, which provide required flow regardless of pressure drop across the valves," says Lieberfarb. "Also, the valves have regulating spools that provide adjustable open areas proportional to the current levels," he notes.

The new valves are rated for pressures up to 3,500 psi and regulated flow rates up to 13 gpm. There are three electro-proportional models: a two-way normally closed, a two-way normally open, and three-way priority normally-closed. The ZL Series valve design is patent pending. The ZL valves also eliminate the need for check valves, according to Lieberfarb. HydraForce Inc. also offers hydraulic controllers designed to work with the ZL valves. Additional applications include material handling equipment and industrial machinery.

Additional Details... Zilek Lieberfarb, HydraForce, Inc. 500 Barclay Blvd., Lincolnshire, IL 60069 Tel:(847)793-2300; FAX: (847)793-0086; website. www.hydraforce.com or Enter No. 508