Pneumatic control systems are commonly used in applications where electrical signals aren’t welcome. Combustible chemical factories, oil processing complexes, and fuel storage depots are industries that choose air-powered signaling over spark-prone electricity, which can cause sparks. Process control is maintained, but there are no electrical hazards anywhere within the danger zone. See ISO 80079-36 for more details on signal processing in combustible atmospheres.

As for hydraulic systems, fluids that refuse to compress like air, we see these all the time in aerospace and mobile power transmission systems. For example, a pilot makes a small adjustment to a course, and a much larger mechanical output moves ailerons and rudders. Smaller actions cause larger responses due to the presence of hydraulic actuators. Exactly the same principle applies to large-bucketed excavators, injection molding equipment, and even those megalithic presses used in machining factories.

By necessity, hydraulics components handle higher pressures, often in the range of thousands of PSI (pounds per square inch), whereas pneumatic system actuators aren’t as robust, and this statement can be backed by science.

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The bulk modulus of elasticity

Expressed as K = - dp / (dV / V0), elasticity is a self-evident property of air (pneumatics) where K = Bulk Modulus (Fluid compressibility), dp = Differential pressure change, dv = Differential volume change, and V0 = Initial volume.

It doesn’t have nearly as much of an impact on hydraulic fluids. Actuators in a closed system compress the chosen fluid medium, then that medium produces a corresponding change in state elsewhere in the equipment, moving a valve, operating an actuator, etc.

For fluid-compressed equipment, this means air and pneumatic actuators compress more, so attributes like load displacement responsiveness and carrying capacity are low to moderate. For hydraulic components, responsive load displacement and much higher load capacities are commonly built into their designs.

Understanding hydraulic components

There’s a hydraulic press in California, the 60K forging press in the Weber Metals factory, that can manipulate 60,000 tons of alloy-shaping fluid power. High-pressure hydraulics pumps produce the energy required to generate this metal-pressing impetus. As determined by the type of hydraulic pump, and there are a few, the brute force nature of the output mechanism exhibits desired loading characteristics and motion-based responsiveness.

Piston-type hydraulic pumps are popular, and there are vane and gear pumps and others. Each possesses its own unique fluid discharge characteristics. A gear system with a fixed displacement design would suit a powerhouse system, whereas a variable displacement reciprocating piston pump would fit in well with mobile hydraulics equipment due to its much more responsive design characteristics.

Problems arise when hydraulic components lack alloy strength. A high-grade 316 stainless steel wouldn’t look out of place on high-pressure hydraulics, boasting corrosion resistance and mechanical strength in fittings and tubing, but the same could be said for carbon steel. A carbon steel, such as SAE 4140, would likely be reserved for valves and other actuators, as it exhibits high tensile strength, perfect for moving large booms on a crane.

Besides the steel backbones built into linear cylindrical mechanisms and turning valves, there are flexible hoses and tubing all over fluid systems. Concerning hard-to-compress oils, these flexible plastics must be fabricated from pliable materials that can resist both oily wear and wall-bulging inner pressures.

Pneumatic-coded industrial processing

Pneumatic process control in explosive atmospheres is a popular application for air power, with systems finding their way onto oil platforms and chemical processing plants. Also, food-safe industrial processing and packaging takes place on sites where hygiene is ruled by numerous safety standards, including the ISO 8573-1:2010 food safety guidelines.

Load capacity, like that found on telescoping crane booms, isn’t the goal this time. Rather, it’s finite control and responsiveness, the manipulation of incredibly precise EOAT (End Of Arm Tooling) mechanisms that function as well as humans. Pneumatic components in this sector are made of oil-resistant plastics and pliable hoses, polymers and thermoplastics that won’t wear when tasked with repeatable production-grade jobs.

Comparable to hydraulics circuits, pneumatic systems use air compressors and receiver cylinders, complete with intricate filtration and moisture removal units. Water is unwanted, but it’s an artifact difficult to eliminate, especially when the compressor is pulling in room moisture along with the air. Industrial components in this equipment assembly must be corrosion-proof. While brass and low-carbon steel are popular, stainless alloys like 304 and 316 are often selected due to their compatibility with food-safe industries.

Choosing the right system for industrial applications

Expect hydraulic systems, valve actuators, and fittings in fluid-based power transmission systems, to use heavier alloys. Stainless and carbon steels are common, the latter used to reinforce valve stems and reduce wear. High temperatures are also generated when fluids are placed under great duress, so metal-encapsulated elastomers and fluoropolymers, PTFE or Teflon, will increase frictionless actuator contact without causing thermally introduced parts brittleness.

Components used to build a high-functioning pneumatics system, air compressor, fittings, and valves, must maintain a well-regulated pressure. Although lower than the pressure flowing within a hydraulics setup, it needs to be precisely maintained so that the robotic limbs and EOAT parts can precisely manipulate tiny product items, assembling them rapidly and without issue.

Whether talking about a new car assembly plant or a food processing facility that’s scaled to industrial proportions, pneumatics equipment works cleanly and precisely. Hydraulics, while it might not always be as clean, needs to be responsive enough to ‘joystick-move’ heavy excavators and aerospace systems, booms, or ailerons, working as one closed-system whole to move multi-tonnage loads.

Hydraulics gear is building the industrial framework of tomorrow, leaving pneumatics components to precisely assemble the equipment and parts that will function as the physical manifestation of that evolving infrastructure.