Hydra-pneumatic cylinders—also referred to as hydro-pneumatic cylinders, air-over-oil cylinders, and intensifier cylinders—combine the power of a hydraulic cylinder with the speed and precision of a pneumatic cylinder. The resultant mixture of force and control makes hydra-pneumatic cylinders ideal for various industrial applications, including punching, riveting, bending, and forming. 


An industrial press — more commonly called a machine press — can perform a broad range of tasks that require the application of pressure to form and shape metal. In addition to forming, industrial presses can accommodate tooling for cutting, assembly, and more. Presses are available in many different sizes and may use various energy sources. There are three types of standard press system frames:
*The H-frame press allows for easy material pass-through; front to back &/or left to right.
*The C-frame press facilitates easy loading/unloading from the front, or from either side.
*The CGB-frame press features a low-profile design and accommodates bench-top use.
The ideal frame and method of applying force will depend on the application. There are five types of industrial presses commonly used in machine shops. 


Actuators are designed to convert energy from different sources, such as electric currents, pneumatic pressure, or hydraulic fluid pressure, into motion. Servo actuators use feedback signals to move or control mechanical systems in a highly efficient and safe manner. This is possible because servo actuators have a controller that can accurately compare, contrast, and calculate the potential differences between the desired results and system conditions on a real-time basis before the motion starts. Servo actuators use a servo motor in either an open or closed-loop control system. Several servo actuator models have a food-grade approved coating of paint for more sanitary wash-down applications.


Aries Engineering Co., Inc. is a diversified manufacturer of “hydra-pneumatic” cylinders and presses designed for use in a wide range of assembly and forming applications. We compiled a list of commonly used manufacturing terms for your reference. This glossary is an easy-to-use guide of key terms.

Term Definition
Accuracy The degree to which the result of a measurement, calculation, or specification conforms to the correct value or a standard.
Actuator A device that causes a linear or rotary motion by converting energy, often electrical, pneumatic, or hydraulic, into mechanical force.
Adjustment barrel The part of a TSL (Total Stroke Limiter) that is threaded, and which is turned to accurately adjust the stroke of a cylinder.
Air over oil cylinder A cylinder that uses a pneumatic operated piston and rod assembly to trap and intensify the oil pressure in an adjacent cylinder body to generate a higher force output than a pneumatic cylinder alone.
Air/oil intensification The technique of transforming a relatively low pressure, long-stroke pneumatic motion into a relatively high pressure, short-stroke hydraulic motion.
Air/oil separation The technique used within self-contained air over oil cylinders which prevents compressed air from getting into the oil section of the cylinder.
Air-oil tandem cylinder A pneumatically powered cylinder coupled to a closed hydraulic cylinder by a common piston rod. The hydraulic section serves to control the speed of the strokes of the cylinder by metering the flow of oil from one side of the hydraulic piston to the other side through a crossover tube with flow controls. It is not an intensifier cylinder.
Algorithm A finite sequence of computer instructions used to perform calculations, data processing, automated reasoning, and other tasks.
Alignment Alignment of the actuator, parallel to the line of motion, is critical. The end effector connection must be designed to prevent any transfer of bending moments back to the actuator.
Anvil In pierce units, it is the side of the mechanism holding the die button, opposite of the ram which holds the punch.
Approach stroke The stroke of a cylinder needed to meet a workpiece, before the work is done. Sometimes called the fast-approach stroke.
B10 Life B10 Life is expressed in total revolutions or inches of travel a system will operate under a rated load. 90% of all systems operated at this rated load will meet or exceed this rating. Although 10% may not reach a million inches, 50% could exceed 5 million inches.
Ball screw A ball screw (or ballscrew) is a mechanical linear actuator that translates rotational motion to linear motion with little friction. A threaded shaft provides a helical raceway for ball bearings which act as a precision screw.
Bearing A machine element that constrains relative motion to only the desired motion and reduces friction between moving parts.
Bending The process of forcing an object from a straight or relatively straight shape into a shape with a curve, or a more exaggerated curve, or adding a curve on a different axis.
Bolster The perforated plate in a punching machine on which anything rests when being punched.
Booster The part of a hydra-pneumatic cylinder that converts air pressure and relatively long displacement into a higher hydraulic pressure with relatively less displacement.
Breather The small port opened to the atmosphere for venting pneumatic pressure, usually through a sintered bronze fitting.
BSPP British Standard Parallel Pipe. Refers to a parallel thread fitting or port that uses an elastomeric face ring on the fitting to do the sealing. Also known as a “G” port, or “ISO G” port.
BSPT British Standard Pipe Taper is similar to NPT, except there are important differences. While not widely used in the USA, BSPT is used in China and Japan.
Bushing A type of vibration isolator that provides an interface between two parts, damping the energy transmitted through the bushing. Or, a cylindrical lining for an opening (as of a mechanical part) used to limit the size of the opening, resist abrasion, or serve as a guide.
C frame press A press which has the shape of the letter C; also referred to as gap-frame presses.
CGB press A compact style of C frame press from HyperCyl whereby the frame is made from a compact, one-piece, flame-cut, steel C frame about the width of its actuator, with an integrated guide mechanism.
Clamping To hold something tightly against or in another thing.
Clinching Also known as press joining, clinching is a high-speed, mechanical fastening technique for point joining of sheet metal components. It is suitable for ductile metal sheets from around 0.5 to 3mm thick and up to a total joint thickness of about 6mm.
Coining A closed die forging process, in which pressure is applied on the surface of the workpiece impressing fine details into the top and/or bottom surfaces of the workpiece in order to obtain closer tolerances, smoother surfaces, and eliminate draft. Closed die forging is a process in which forging is done by placing the workpiece between two shaped dies.
Compressed air Air that has been compressed by a mechanical means to a pressure that is significantly higher than atmospheric pressure. Compressed air is applied to one side and exhausted from the other side, of pneumatic cylinders to do work.
Coupling A device that serves to connect the ends of adjacent parts or objects.
Cpk Process Capability Index. It is a statistical tool to measure a producer’s capability to produce a product within the customer’s tolerance range.
CPM Cycles Per Minute
Cylinder A linear actuator that uses fluid power (hydraulic or pneumatic) acting on an internal piston to move a load. A cylinder is composed of an external tube, an internal piston to which a rod is attached, a head end, and a cap end usually held together by tie rods.
Cylinder cap The end of the cylinder from which the work rod or ram does not protrude. The opposite end of the rod end, or head end, of a cylinder.
Cylinder head The end of the cylinder from which the rod or ram extends. Same as the rod end of the cylinder.
Die button A hardened steel that provides the opposing cutting edge for a punch during the punching process. During this operation, the slug or blank being stamped passes through the opening of the die button.
Die set coupling A kind of alignment coupler for connecting a cylinder rod to a die set, or another tooling, to allow some radial and axial misalignment compliance, preventing side load back to the cylinder.
Die spring A spring for providing resistance to motion prior to breaking through in a punching or piercing application.
Directional control valve A device that controls the flow of pneumatic or hydraulic fluid into, or out of, ports of a pneumatic or hydraulic actuator.
Displacement 1. The amount of fluid it takes to cycle a cylinder, usually measured in cubic inches, cubic feet, or cubic centimeters.  2. Or, it is also used synonymously with a distance traveled or “stroke.”
Draft The amount of taper given on the sides of the part required to remove it from the die.
Dynamic load rating A calculated, constant radial load that a group of apparently identical bearings will theoretically endure for a rating life of one million revolutions. The dynamic load rating is a reference value only.
Electro-mechanical Relating to or denoting a mechanical device that is electrically operated, as opposed to pneumatic or hydraulic.
Equalizing A technique for bringing both sides of a pierce unit against the workpiece without moving the workpiece, prior to punching.
Fast-approach stroke The stroke of a HyperCyl cylinder needed to meet a workpiece, before the work is done. Sometimes called the approach stroke.
Fluid A substance that flows, such as gasses or liquids.
Folding A technique of metalworking whereby metal is folded, repeatedly forged and annealed, and unfolded, at which stage it generally has a dramatic new three-dimensional form.
Force When calculating the required force, consider the force to accelerate the mass as well as the force to overcome the friction and the applied force. For sizing the system, consider the maximum force and duration. For evaluating life under varying loads, calculate the root mean cube equivalent load which weights the different load levels by the typical length traveled under that load.
G port A port in a pneumatic device with BSPP (non-tapered) threads designed for BSPP fittings with elastomeric face seals.
Gage  An instrument with a graduated scale or dial for measuring or indicating a quantity.
H frame press A press with the shape of the letter H.  It can have two side posts or 4 side posts.
Hemming A process in which metal is folded over onto itself to create a smooth edge or strengthen the part. Hemming also can be used to join two parts together.
High pressure stroke The amount of stroke required under high pressure, typically factored for hydra-pneumatic cylinders.
HMI Human Machine Interface
Hose  The reinforced flexible conduit of a satellite hydra-pneumatic cylinder system that connects the booster with the work cylinder.
Hydra-pneumatic cylinder A completely self-contained, air over oil intensifier cylinder which produces a relatively high force work stroke.
Hydraulic Pertaining to a mechanical function operated through the force of liquid pressure (usually oil).
Hydraulic cylinder A cylinder designed to function under liquid pressure, usually hydraulic oil.
Hydraulic power unit A bulky, heat-producing, noisy device with a reservoir, motor, and a pump that is used to apply the pressurized liquid (usually oil) to hydraulic actuators.
Hydro-pneumatic cylinder Another name for hydra-pneumatic cylinders.
HyperCyl The name brand of Aries Engineering Co. of Dundee MI, USA, for medium to high force hydra-pneumatic actuators up to 200 tons, and servo actuators up to 25 tons.
Impact Impact is unacceptable to ball screws as well as anti-friction bearings. Severely shortened life and/or catastrophic failure are the results. Avoid impact or provide a mechanical system to buffer the ball screw assembly from shock loads. Impact loads are generally acceptable for air-oil units as the oil provides a cushion due to incompressibility preventing damage to the cylinder.
Inline To have the characteristic of being in one line or axis.
Intensification The action of making a fluid pressure in an enclosed system go substantially higher.
Intensifier cylinder A cylinder which intensifies the fluid pressure on the work piston in order to produce a higher output force.
Kilonewton A unit of force measurement. One kilonewton = 224.8 pounds-force.
Linear velocity Linear velocity is limited by (1): the maximum ball screw rpm without “whipping” of the ball screw shaft; (2) critical speeds for the ball nut assembly (beyond which the motion of the balls becomes erratic and performance life suffers).
Load cell A force transducer that converts a force such as compression into an electrical signal which can be measured and standardized.
Locking ring A type of jam nut used on the top of the adjustment barrel of a Total Stroke Limiter, which is used to lock the adjustment in place.
LVDT Linear Variable Displacement Transformer, (or Linear Variable Differential Transformer, or Linear Variable Displacement Transducer) is a device for converting a linear displacement into a proportional electrical signal for measuring direction and distance.
Marking A technique of impressing letters, figures, or texts into the surface of workpieces for the purpose of identifying workpieces, giving sequences for assembly operations, or durably noting down dates of manufacture.
Maximum operating pressure The maximum pressure at the ports for which a fluid power device is designed or tested by the manufacturer. Usually, this pressure should not be exceeded.
Minimum operating pressure The minimum pressure at the ports for which a fluid power device is designed or tested. The device may not work properly unless at least this pressure is used.
Misalignment The inaccurate axial or radial position of something in relation to something else.
MOP Minimum Operating Pressure
MTBF Mean Time Between Failure
NFPA National Fluid Power Association
Notching A shearing-related metalworking process that involves the use of a punch press to selectively cut unwanted material from the outer edges of a workpiece.
NPT National Pipe Tapered threads. It is a U.S. standard for measuring tapered threads on threaded pipes and fittings. Unlike straight threads found on a bolt, a taper thread will pull tight, making a closer seal.
Pierce unit A mechanical device for piercing or punching holes in a workpiece.
Piercing A shearing process in which raw metal is pierced with a machining tool, resulting in the creation of a circular or other shaped hole. As the raw metal is pierced, the metal from the newly created hole is considered scrap. Often, the terms “piercing” and “punching” are used interchangeably.
Platen The movable table of a machine, on which the work is fastened and presented to the action of the tool. A flat plate, especially one that exerts or receives pressure.
PLC Programmable Logic Controller. The PLC takes inputs, performs logic on the inputs in the CPU, and then turns on or off outputs based on that logic.
Pneumatic Containing or operated by air or gas under pressure.
Pneumatic cylinder A cylinder operated by compressed air.
Port The connection on a fluid power component that allows flowing into, or out of, the device. Typically, a port is female and is tapped NPT, BSPT, SAE, or BSPP.
Pound-force The amount of force equal to the gravitational force applied on a mass of one pound on the surface of Earth. One pound-force is about 4.448 newtons.
Power stroke The stroke distance of the cylinder needed to perform the intended task under full force loads. The power stroke is accomplished within the total stroke of the cylinder.
Pressing To move or cause to move into a position of contact with something by exerting a physical force.
PSI Pounds per Square Inch. A unit of measurement of pressure of a fluid.
Punching A forming process that uses a punch press to force a tool, called a punch, through the workpiece to create a hole via shearing. Punching is applicable to a wide variety of materials that come in sheet form, including sheet metal, paper, vulcanized fiber, and some forms of plastic sheet. The punch often passes through the work into a die. Often, the terms “piercing” and “punching” are used interchangeably.
Quadrature encoders An incremental encoder that lets you measure the speed and direction of a rotating shaft (or linear motion) and keep track of how far you have moved.
Ram A rod of a cylinder that is at least one-half the diameter (or more) of the piston area.
Repeatability The closeness of the agreement between the results of successive measurements of the same measure, when carried out under the same conditions of measurement. This is sometimes called test-retest reliability.
Reservoir A place where something is stored, such as a part of an apparatus in which a liquid is held as a supply or in reserve.
Retract stroke The stroke of a cylinder returning the rod back to the home, or retracted position.
Riveting Fastening with a headed pin or metal bolt used for uniting two or more pieces by passing the shank through a hole in each piece, and then deforming the plain end so as to make a second head.
Rod lock A mechanical device on the head end of a cylinder that grabs the rod when supplying air pressure to the rod lock drops below a minimum operating pressure. Usually, a rod lock is spring-loaded.
Roller screw A roller screw is a mechanical actuator similar to a ball screw that uses threaded rollers (instead of balls) as the load transfer elements between the nut and screw.
Satellite Something dependent or controlled by another entity.  A HyperCyl satellite series cylinder (HPS) has a separate work section controlled by the booster to which it is attached by a hydraulic hose.
Self-contained Having the reservoir of oil contained within the cylinder itself, and not having an external reservoir.
Separator block A block in a HyperCyl cylinder which separates the pneumatic high-pressure piston section from the reservoir section.
Serial number A discreet, unique number for a manufactured item by which the item’s date of manufacture and all its attributes can be identified.
Service ratio In hydra-pneumatic cylinders, the ratio of hydraulic pressure (in psi) in the work section, generated by the pneumatic pressure on the high-pressure piston. For example, a 10:1 ratio means that 10 psi hydraulic pressure is generated by every one psi pneumatic pressure applied to the high-pressure piston.
Servo A servomechanism, often shortened to servo, is an automatic device that uses error-sensing negative feedback to correct the action of a mechanism.
Side loading A force applied to a linear actuator radially, rather than along the intended axis of motion. It can be generated from an unsupported offset load, insufficiently fixed mounting, or external loads pushing against the actuator.
Soft touch The characteristic of meeting the workpiece with low force (and sometimes low speed) before the high force work is done to the workpiece.
Staking A method of joining in which one workpiece has a hole in it, while the other has a boss that fits within the hole. The boss is very slightly undersized so that it forms a slip fit. A staking punch is then used to expand the boss radially and to compress the boss axially, so as to form an interference fit between the workpieces. This forms a permanent joint.
Stamping A manufacturing process used to convert flat metal sheets into specific shapes.
Stiffness System stiffness is an essential attribute of high accuracy positioning systems. Specifying 0.0002-inch positioning accuracy and repeatability without considering spring rate may result in a disappointing performance. For precision light-duty applications a spring constant of 1 x 106 lbs/in is acceptable and a range of 3 x 106 to 6 x 106 lbs/in may be necessary for higher load applications.
Tandem Having two things arranged one in front of the other, or alongside each other. HyperCyl provides a Tandem cylinder called the HPT (Link Here, )
Tensile strength A measurement of the force required to pull something such as rope, wire, or a structural beam to the point where it breaks.
Threshold sensor A threshold sensor provides a pneumatic or electronic output when the port it is sensing has little to no pneumatic gauge pressure. It sends a signal in the absence of pressure.
Tie rods In actuators, the four or more threaded rods that run the length of the entire cylinder assembly which hold the head end, cylinder tube(s), and cap end of the assembly together.
Ton In U.S.A. and Canada, a unit of force measurement equivalent to 2000 pounds force. Sometimes called a short ton.
Torque A measure of the force that can cause an object to rotate about an axis.
Total stroke The entire stroke of the cylinder. The approach stroke and the power stroke are done within the total stroke of a HyperCyl cylinder.
Total stroke limiter An adjustable stop for a cylinder’s stroke.  A “TSL” consists of an adjustment barrel and locking ring threaded to a secondary piston rod extending from the cap end of a HyperCyl cylinder.
Valve block The valve block in a HyperCyl hydra-pneumatic cylinder is the section of the cylinder which, when the high-pressure rod is extended, seals on the high pressure rod, trapping the oil in the work section, and allowing the oil to be intensified.
Vent port fitting A small plug threaded into the hydraulic cap of the booster, or the hydraulic end of the work section, which can be loosened to allow the venting of air from the oil.
Welding A fabrication process whereby two or more parts are fused together by means of heat, pressure, or both; this process forms a joint as the parts cool.
Wizard A help feature of a software package that automates complex tasks by asking the user a series of easy-to-answer questions.
Work cylinder The section of a hydra-pneumatic cylinder that has the work rod (or ram), and which is distinguished from the booster section of the cylinder.
Work rod The rod of the cylinder which does the desired work.  It is also often called the ram.
Working ratio The ratio of pounds force generated by the cylinder is proportional to the pressure on the high-pressure piston. For example, a working ratio of 54.54:1 means the cylinder will generate 5,454 pounds force when 100 psi is applied to the high-pressure piston.