By Josh Cosford, Contributing Editor
The hydraulic designer most frequently creates a hydraulic schematic to represent the entirety of the hydraulic pumps, valves, actuators, accessories, and plumbing of a machine. After the first sketch is pencilled, the circuit is migrated to CAD software for refinement, while the bill of materials is systematically populated to reflect all the chosen major components. A few revisions later, due to unexpectedly expensive items or those with unacceptable lead times, many designers will move on to the next project.
What’s not on the schematic, and perhaps of little care to the designer, is the plumbing and connections used on the real-life machine. Often, these decisions are left to the technician building the machine or power unit, which, depending on the size of your company, might be subject to “whatever’s in stock” and can be made to work with the inventory available on that particular day. Furthermore, technicians have their preferences, so without thoughtful planning of the plumbing aspect of machine design, you may have two entirely differently plumbed machines should another make its way down the pipeline.
In reality, hydraulic fittings and adapters should be part of the design process, which not only provides the most efficient build but also a consistent appearance using the fewest SKUs possible. A hydraulic design should be comprehensive and consider the best combination of effective fittings that balance cost and performance, while also being sensitive to the region to which the machine is shipped, if not local.
The designer must ensure that the chosen fittings and adapters are suitable for the working environment, which includes ambient conditions, fluid compatibility and pressure rating. Many fittings come standard as nickel or zinc-plated steel, but corrosive or oxidative ambient conditions may call for stainless steel. The designer should bear the responsibility of adhering to risk-based regulations, such as EU REACH or American TSCA, to avoid selecting fittings and adapters that contain banned substances in their manufacture or plating.
There are many thread standards to choose from, and the designer knows they are not created equally. Sure, NPT is inexpensive and readily available, but it is designed for a one-and-done installation and is not intended for regular servicing and disconnection. Soft seal technology rules the day, so look for ORB port fittings with ORFS (O-Ring Face) fittings that are reliably leak-free for the life of the machine. Is the machine going to Europe or Taiwan? Be aware that fitting preference aligns geographically, so BSPP should be installed for machines heading to Europe, while BSPT (British Taper) might be more suitable for Taiwan.
Once the construction type and standard are defined, the designer must understand the nature of the plumbing layout on the machine. Preselecting the appropriate elbows, tees, and adapters that best suit the porting of the pumps, manifolds, and actuator orientations should be part of the design stage and not relegated to the technician. For example, a vertically mounted cylinder with horizontally oriented ports should include a 90° adapter so that the hose hangs with no radial stress. Selecting these fittings ahead of time limits the guesswork during installation, and also avoids any surprise rat’s nests that appear when multiple fittings and adapters are joined together to create the result of an intelligently planned single fitting.
Probably the most underestimated criterion the designer is responsible for is the sizing of fittings and adapters. The designer has the opportunity to select a size appropriate to the circuit’s flow rate, which ensures fittings are large enough for the related flow but not oversized, thereby not detracting from the budget. And with appropriately sized fittings comes appropriately sized plumbing, so you must view all of the fittings, hoses and tubes holistically.
Once the BOM is complete with the list of fittings and adapters, the designer or buyer may send out the RFQs to their preferred suppliers to bid against, which ensures you can not only select the best price and lead time, you don’t have to worry about the last minute surprises of low stock or poor selection, which both lead to poorly plumbed machines. If you’re a designer not already selecting fittings and adapters, consider taking on this responsibility to enhance your capabilities while reducing costs and lead time for your employer.
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