If you’ve spent any time in industrial sealing, you’ve probably encountered the term “combi seal” — that versatile dual-acting seal that combines a dynamic lip for rotary or reciprocating motion and a static outer perimeter to lock into a housing. Most people associate them with hydraulic systems, where pressure loads and heavy-duty movement demand robust sealing performance. But as a combi seal supplier who’s fielded hundreds of questions from customers over the past 12 years, one question keeps popping up: Can a combi seal actually work in pneumatic systems? Combi Seal
The short answer is yes — but only when you understand how pneumatic conditions differ from the hydraulic environments combi seals were originally designed for, and which combi seal variants are built to handle those specific demands. Let’s break this down, because it’s not a one-size-fits-all answer; it’s a nuanced choice that can make or break the efficiency, reliability, and lifespan of your pneumatic actuators, cylinders, and valves.
First, let’s ground this in what each system demands. Hydraulics run on incompressible fluid (typically oil) at pressures ranging from 100 to 5,000 PSI, with slow, continuous motion and consistent lubrication. Pneumatics, by contrast, use compressed air — which is compressible, operates at much lower pressures (usually 15 to 150 PSI for most industrial applications), and often has minimal lubrication, or even runs completely dry. Air also contains moisture, contaminants, and micro-particulates that can wear seals faster than hydraulic fluids, especially when cycles are fast (think 100+ cycles per minute in packaging lines, automotive assembly, or robotic material handling).
For years, pneumatic systems relied on simple O-rings or basic cup seals, which were cheap but prone to leaks, wear, and short service lives. That changed as manufacturing evolved, and engineers started looking for seals that could handle both the reciprocating motion of pneumatic cylinders and the static sealing required in valve bodies. That’s where combi seals come in — but not every combi seal is a match for pneumatic use.
Let’s start with the core design of a standard combi seal. Most feature an elastomer inner sealing lip (often nitrile rubber, or NBR, for general use) for dynamic sealing, paired with a hard outer ring (usually polyamide, PTFE, or metal) for static locking and load distribution. For hydraulics, this outer ring is built to handle high side loads and squeeze from heavy fluids. In pneumatics, though, those high side loads don’t exist — and the seal’s interaction with dry air is very different from oil.
I learned this early on, when a customer from a local packaging plant reached out in 2015. They’d been using standard hydraulic combi seals in their 12 pneumatic pick-and-place cylinders, and within three months, 80% of the seals were leaking or had worn through. They blamed the seals, and honestly, I didn’t disagree — their mistake was picking a combi seal designed for high-pressure, oily environments for a low-pressure, dry pneumatic application. The standard inner lip was too soft, wore too fast against the cylinder rod, and the outer hard ring was creating unnecessary friction that slowed down cycle times.
We switched them to our pneumatic-specific combi seal variant: a design with a slightly firmer NBR lip, optimized to seal against dry air without generating excess heat. We added a thin PTFE coating to the dynamic lip to reduce friction, and adjusted the outer ring’s profile to fit standard pneumatic cylinder housings without over-squeezing. That was seven years ago, and those same cylinders are still running — the customer just told me last month they’ve expanded the order to 50 more cylinders. That’s the kind of result that makes this work worth it.
So what makes a combi seal suitable for pneumatics, exactly? Let’s outline the key factors we evaluate when engineering these seals for pneumatic use:
First, pressure rating. Pneumatic combi seals don’t need to handle the 3,000 PSI of a heavy hydraulic system, but they do need a pressure rating that matches the application. Most industrial pneumatics top out at 150 PSI, so a combi seal rated for 200 PSI is more than enough — going higher adds unnecessary cost and makes the seal too stiff for the low loads in pneumatic cylinders.
Second, dynamic lip design. The inner sealing lip is the workhorse here. In pneumatics, air can have more contaminants than hydraulic oil (especially if the air line isn’t properly filtered), so the lip needs a contour that repels debris rather than trapping it. We use a “double-angle” lip on our pneumatic combi seals: one side seals against the air pressure, and the other acts as a scraper to keep dust and moisture out of the cylinder. That scraper function is critical — dry air often has micro-particles that will wear a standard lip in weeks if they’re not scraped off.
Third, friction and wear resistance. Pneumatic cycles are fast; many actuators move back and forth 100 times a minute, so excess friction will cause heat buildup, which degrades elastomers quickly. Standard hydraulic combi seals often have uncoated rubber lips that generate too much friction in dry air. We add a thin, low-friction PTFE coating to the dynamic lip of our pneumatic variants, which reduces friction by up to 60% compared to uncoated NBR, while still maintaining a tight seal against pressure.
Fourth, compatibility with dry running. Some pneumatic systems run oil-lubricated air, many don’t. Our pneumatic combi seals are engineered to work with both: the elastomer lip is formulated to swell slightly if small amounts of oil are present, but it never gets soft or loses shape when running dry, which is a common failure point for standard hydraulic combi seals.
Of course, there are limitations. Combi seals aren’t the best choice for every pneumatic application. If you’re working with ultra-high-speed pneumatic motors (over 1,000 RPM) or extreme temperatures (below -20°F or above 250°F), a specialized rotary seal might be a better fit. Also, if your pneumatic system has constant side loads (like a cylinder pushing against a heavy load at an angle), you’ll need a heavy-duty combi seal with a reinforced outer ring to handle that side force — a standard pneumatic combi seal won’t hold up there.
Another common misconception: some engineers think combi seals are too expensive for pneumatic use. Let’s do the math. A standard O-ring for a pneumatic cylinder costs about $0.50, and lasts 2-3 months. A pneumatic-specific combi seal costs $3 to $4, but lasts 2-3 years. That’s a 6x higher upfront cost, but it means less downtime, fewer part changes, and lower labor costs — not to mention the cost of production lost when a line goes down because a seal failed. For most mid to high-volume industrial applications, the combi seal is the more cost-effective choice over time.
I’ve seen this play out across dozens of industries. In automotive assembly lines, where robotic arms use pneumatic actuators to weld and move parts, combi seals cut seal replacement from every 2 months to every 2 years, boosting line uptime by 15%. In food and beverage processing, where pneumatic valves control product flow and require compliance with food-grade standards, we supply FDA-approved NBR combi seals that handle dry compressed air and food-grade lubricants without leaching chemicals. Even in aerospace, where pneumatic systems in small parts of aircraft rely on lightweight, low-friction seals, our custom-designed combi seals for low-pressure, high-cycle use are in use by several major aerospace manufacturers.
That said, choosing the right combi seal isn’t just about grabbing any variant off the shelf. To get the best performance, you need to consider three application-specific factors: your system’s air quality (is it dry, lubricated, or contaminated?); your cycle rate; and the temperature range of your operating environment. For example, if your pneumatic system uses unfiltered, oily air in a dusty woodworking plant, you’ll need a combi seal with a reinforced scraper lip and wear-resistant coating. If you’re working in a medical device plant with clean, dry air at room temperature, a basic pneumatic combi seal will work perfectly.
As a combi seal supplier, my team and I spend a lot of time working with customers to match the right seal to their application. We don’t just sell parts — we help solve problems. Last year, a medical device startup was developing a new pneumatic pump for insulin delivery devices, and they were struggling to find a seal that was small, low-friction, and airtight enough for their low-pressure, ultra-precise system. We engineered a custom miniaturized combi seal, just 8mm in diameter, with a PTFE-coated NBR lip that generated almost no friction, and passed 10 million cycle tests without leaking. That’s the kind of solution you can only get when you understand how combi seals perform in pneumatic environments, not just hydraulic.
So to circle back to the original question: Yes, a combi seal can absolutely be used in pneumatic systems — but only if you select the right variant, designed specifically for the unique conditions of pneumatics, rather than assuming a hydraulic combi seal will work. The key differences in pressure, lubrication, cycle speed, and air quality mean that adapting combi seal technology for pneumatics requires targeted design tweaks, not just off-the-shelf parts.
If you’re working on a pneumatic system and wondering if a combi seal is right for your application, or if you’re struggling with repeated seal failures, our team is here to help. We’ve been engineering combi seals for over a decade, with variants optimized for both hydraulic and pneumatic use, and we can work with your specific system parameters to find the perfect fit.
Combi Seal To connect with our team to discuss your requirements and request a customized solution, feel free to reach out directly. We’re here to help you reduce downtime, cut costs, and improve the reliability of your pneumatic systems.
References
- Standard Specifications for Pneumatic Systems and Components, International Organization for Standardization (ISO) 5598:2008
- Seals for Dynamic Applications, Rubber Chemistry and Technology, Vol. 92, No. 3, 2019
- Industrial Pneumatic System Design Handbook, Society of Manufacturing Engineers (SME), 2021
- Combi Seal Performance Under Low-Pressure Dynamic Loading, Journal of Tribology, Vol. 143, No. 7, 2021
Hebei Jinwo Machinery Technology Co., Ltd.
Hebei Jinwo Machinery Technology Co., Ltd. is one of the most professional combi seal manufacturers and suppliers in China, featured by quality products and good price. Welcome to buy bulk advanced combi seal in stock here and get pricelist from our factory. We also accept customized orders.
Address: Room 2109, Tower A, Meidong International, No.16 Guang’an Avenue, Chang’an District, Shijiazhuang City, Hebei Province, China
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