As engineers, we know that it pays to plan ahead. There simply isn’t a better business rule that will help us save time and money, avoid problems down the road or just build a better solution. Case in point: plan ahead for hydraulic applications that ultimately require non-standard tube fittings.
Let’s look at a hypothetical story of a newly designed hydraulic application. It’s nearly complete except that it requires a fitting to connect a one-half inch tube to a one-eighth inch port. Unfortunately, there is no one standard fitting on the market that will make this particular connection. The solution? The machine design team decides, for the sake of expediency, to ‘stack’ three or four standard fittings together.
The better solution would have been to ‘jump’ to a custom fitting. The new fitting may cost a little more than a single standard fitting, but overall, it’s a cheaper and more effective solution. The photo above shows an example of multiple stacked fittings along side a non-standard part with the same end types and sizes.
Stacking’s impact on leak paths and hydraulic machine performance
The one and only advantage to stacking – the fact that standard, readily available parts can be used – pales in comparison to the problems that can result from this configuration.
Leak paths top the list of concerns, and believe it or not, one small leak can quickly become costly (Oil Leak Calculator). Consider the fact that any time fittings are connected, you have a potential leak path, and anywhere you have a potential leak path, that’s an inspection point. When three or four fittings have been stacked together, the number of inspection points increases along with the number of connections that must be torqued down correctly to ensure leak-free reliability. In other words, stacking has a kind of multiplier effect on leak paths – an issue that could result in increased warranty claims and environmental pollution.
Another negative side effect of stacked fittings has to do with equipment performance. Additional connections can lead to flow path obstructions and more abrupt walls – both of which have a tendency to reduce fluid flow. A larger pump may be an easy fix to this problem, but of course it comes with a heftier cost.
Example of stacked fittings in a customer application.
Planning ahead for customized fittings
I get it. Fittings are one of the last things that engineers think about. But rather than waiting and hoping to just grab some parts off the shelf, it’s worth the effort to look at the fitting requirements early and order the exact parts needed to get the job done right. And even though that one-off custom part may cost more per part than standard fittings (e.g. $10 vs. $4 per part), you may end up saving money by using just one custom part rather than multiple standard parts.
The only real differentiator is timing. Whereas standard parts are more likely to be available, custom parts may take about two or three weeks to manufacture. Rapid service options for custom fittings are also available when you are in a pinch.
When time is an issue
The message here is simple: plan ahead and, whenever possible, jump, don’t stack! Non-standard fittings may seem like such a small detail in the scheme of things, but a little pre-planning goes a long way in saving money, avoiding trouble and, most importantly, designing a better system.
Got an interesting stacking story?
Send me your best (or worst!) example of stacked fittings. Let’s share some inspection nightmares from the field.
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If you have any questions or comments, please post them and I’ll respond if warranted. If you want to talk to me directly, I can be reached at Parker Tube Fittings Division, 614.279.7070, or via email. Click here for a print-friendly PDF version of Hydraulic Fittings: Don't Stack, Jump!
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Nathan Green, Engineer, Parker Tube Fittings Division