Hydraulic integrated circuits consist of a manifold and multiple cartridge and/or subplate mounted valves contained in a single assembly that can drastically reduce the number of fittings and lengths of hose and tubing otherwise required for circuits using line-mounted components.
Even people with virtually no knowledge of electronics realize what a tremendous impact integrated circuits have had on just about every product in consumer electronics — small size, light weight, fewer components, and lower cost. Although the effects of hydraulic integrated circuits (HICs) are not as dramatic as those in the world of electronics, they still can substantially reduce the size, complexity, and overall cost of hydraulic systems. Furthermore, HICs exhibit additional advantages that go beyond these benefits.
An HIC consists of a manifold containing multiple pressure-, directional-, and even proportional-control valves. In extreme cases, an HIC may even contain pumps, filters, actuators, or any combination of these to form a completely self-contained hydraulic system. Most HICs, however, consist of a manifold containing inlet and outlet ports, cartridge and subplate mounted valves (or both), and a network of internal passages that route hydraulic fluid through branch circuits of the hydraulic system.
Sizing up the benefits
Conventional hydraulic systems use hose and metal tubing to route hydraulic fluid from a hydraulic power unit (HPU) to a variety of valves and actuators, and back to the HPU. With an HIC, hose and tubing still routes fluid from the HPU to a variety of valves, but most of these valves may be contained within a single manifold tucked away in an available space on a machine.
With a conventional system, the line-mounted valves take up more space than cartridge valves, so they may end up being installed at many different locations throughout a machine. This complicates troubleshooting and maintenance and can require installing hoses in locations where they could be struck by foreign objects or otherwise damaged by ambient conditions.
Although the time to design the HIC and machine the manifold are additional expenses for the initial system, Dick Simoni, vice president, R. L. Miller Inc., Pittsburgh, says this cost usually is more than offset by the lower cost of cartridge valves, reduction in the cost of required hose, tubing, and fittings, and the much lower cost of assembly and installation. This means benefits like a lighter, more compact system and easier maintenance come at no additional cost.
Simoni adds that troubleshooting can be easier with an HIC because multiple valves, switches, and test points may all be located within close proximity to each other, instead of being located throughout a machine. Furthermore, he says eliminating hose and tubing assemblies and fittings reduces the potential for leakage and component failure, so less maintenance is required and reliability is improved.
Beyond breaking even
However, Simoni explains that you shouldn't expect to integrate all in-line valves into HICs. "The break-even point must be considered when making a switch to integrated circuits. The financial advantage to using HICs depends on quantity — but not in the usual sense that unit cost decreases as the number of units increases.
"From the aspect of quantity," continues Simoni, "mine equipment, for example, would not seem to be a viable application because only a few units of a particular machine are manufactured annually. But HICs are effective here because one machine — such as a roof bolter — contains so many components that can be incorporated, integrated, or eliminated.
"We may provide a specific HIC only two or three times a year, so there's no way a custom-made block will be more economical than off-the-shelf components. However, the installed cost of the block with the many cartridge valves can be much less than the numerous individual valves, fittings, hose, and the cost to install them would've been. What's more, the HIC adds even greater value throughout the life of the machine because a cartridge valve can be replaced at a fraction of the cost of its in-line counterpart — and without even having to disconnect a single hose!"
Make it a ductile
Mention a custom-machined manifold, and a block of steel comes to mind for most people. However, for the past few decades, ductile iron has served as a cost effective alternative to carbon steel. Although people often perceive any cast iron as hard, brittle, and difficult to machine, Bob O'Rourke, of Dura-bar Div., Wells Mfg., says that "cast iron" represents a wide range of materials with tensile strengths ranging from 10,000 to 250,000 psi, depending on how it is cast and heat treated.
O'Rourke explains that ductile iron is a continuous-cast material with strength comparable to that of plain carbon and free-machining steels. However, because it is more machinable than steel, ductile iron can save substantial cost by reducing machining time, extending tool life, or both.
Along with better machinability, ductile iron also produces fewer burrs from drilling, reveals Gordon Weiler, of Daman Products Co., Mishawaka, Ind. Hydraulic manifolds usually require many intersecting holes, so complete burr removal is essential, but it can add substantial cost to a manifold. However, burr removal is easier with ductile iron, which further adds to cost savings, especially with manifolds.
Another benefit, adds Bill Calcagno, of Selling Precision, West Milford, N.J.,a producer of custom hydraulic manifolds, is that unlike hot-rolled steels, continuouscast ductile iron does not require ultrasonic testing prior to machining. He says that hot-rolled steels contain sulphur and other agents to enhance machinability. However, these agents can produce inclusions — discontinuities or cavities within the structure that could turn a highly machined manifold intro scrap. Because 65-45-12 ductile iron (the type most widely used for hydraulic manifolds) does not require these machinability agents, manifold producers generally can forego the expense of ultrasonic testing.
However, Calcagno explains that ductile iron cannot replace steel in every instance. "If you'll be welding something to a machined manifold, you'll go with steel because it has much better weldability. The additional cost to weld ductile iron more than offsets any cost advantage from machinability in most cases."
Finally, Weiler points out that another reason for the more widespread use of ductile iron is availability. "Size often dictated whether we would use steel or ductile iron. If a manifold had to be larger than a certain size, we had to go with steel. Now, however, we've been able to make manifolds with a cross section as large as 25 in. square, and we anticipate being able to continue increasing that."
For more technical information on ductile iron, visit www.ductile.org. In addition to explaining the technology, properties, and characteristics of ductile iron, this website also offers a comprehensive eBook, Ductile Iron Data for Design Engineers, that can be downloaded for free.