Split-Type Pneumohydraulic Cylinders: 7-Step Guide

Engineering Guide · Pneumohydraulic Systems

Split-Type Pneumohydraulic Working Cylinders, AT & HZ Series are easiest to specify when the whole pressure-to-process chain is treated as one machine subsystem. This guide explains the operating logic, interface checks, commissioning evidence, fault isolation, and safety boundaries that sit around the cylinder catalogue.

What a Split-Type Working Cylinder Actually Changes

Split-type working cylinders separate the high-force actuator at the tool from the air-oil drive unit that creates hydraulic pressure. Their connecting hydraulic line lets a machine builder fit a compact cylinder into a restricted station while placing valves, service points, and the drive where access and cooling are easier.

Separation changes packaging, not physics. Compressed air still supplies the power source, hydraulic fluid transfers pressure, a piston converts that pressure into linear motion, and the piston and rod transmit mechanical force to the tooling. Every interface between those elements can change the installed result.

That boundary matters because a buyer can choose the correct cylinder bore and still miss the cycle target. Long or poorly routed lines can slow pressure build-up. Misaligned guidance can turn axial load into side load. Valve sequencing can interrupt the power stroke. Frame flexibility can absorb motion that should have reached the workpiece.

Terminology boundary. A hydraulic cylinder uses pressurized liquid as its working medium, while pneumatic systems use compressed gas for actuation. In a pneumohydraulic arrangement, the two domains meet without turning the tool-side unit into a conventional plant hydraulic cylinder. Search phrases such as “series pneumohydraulic cylinder” or “single cylinder booster” do not define the actual circuit. Drawings must show the diameter of the cylinder, the position of the piston at each transition, and which side of the cylinder receives pressure.

When a piston reciprocates inside the cylinder, single-acting cylinders, double-acting designs, and a single-rod layout produce different push and pull behavior. The cylinder end, external guide, and port arrangement affect mounting, while operating speed and high-speed approach depend on flow and control timing. Buyers seeking a compact package or long service life should still review moving components, energy efficiency, the force generated at the stated pressure, and how retraction is achieved. Naming the mechanism cannot replace these checks.

Search-language variants such as “piston and the cylinder” and “end of the cylinder” are not drawing definitions. Engineering documents should identify the piston, chamber, rod, cylinder end, and pressured side explicitly.

Packaging scenario. One machine builder has only 190 mm behind a clinching tool, while the valve cabinet has service space 1.4 m away. Placing the working cylinder at the tool and the drive unit near the cabinet resolves the envelope conflict, but it creates a documented hose route, two accessible pressure measurement points, and a recovery-time check. If the team treats the line as an afterthought, the first dry cycle may look normal while the loaded power stroke arrives late. Release therefore waits until the line, controls, guidance, and representative workpiece cycles are included in the test.

For the wider architecture choices, the pneumohydraulic drive cylinder family overview shows where split and integrated arrangements sit. This article stays with the split system and deliberately leaves AT/HZ model comparison and quotations to the commercial page.

The Five-Node Pressure-to-Process Chain

Called the Five-Node Pressure-to-Process Chain, this measurement map covers plant air, the drive unit, the hydraulic line, the working cylinder, and the tool with its controls. System readiness requires a defined input, observable output, and recorded evidence at every node under the same operating cycle.

How does a hydro pneumatic cylinder create high force?

Hydro pneumatic cylinders use compressed air to drive an air-oil intensifier or booster stage. Resulting hydraulic pressure acts on the area of the piston inside a cylinder, so output force rises with pressure and effective piston area. Approach motion can remain fast at low force, followed by a shorter high-force power stroke. That pressure path must still be measured at the machine because line losses, opposing loads, and tool compliance separate theoretical output from released process force.

This arrangement reduces continuous hydraulic-power demand, yet it does not make the actuator a conventional hydraulic system or remove the need to check air flow, oil volume, transition timing, and retraction force. During approach, the piston and rod move toward the workpiece before the control sequence triggers intensification. Return behavior depends on cylinder type and circuit: some designs use pneumatic return, others may use spring force or a powered chamber. That distinction changes retraction force, ports, sensors, and recovery. Treat “single acting cylinder,” “double-acting cylinders,” and “air oil cylinder” as architecture clues, then confirm the actual drawing rather than inferring motion from a search label.

Use theoretical force as the first calculation: F = P × A. For an illustrative 80 mm cylinder bore, piston area is π × 0.08² ÷ 4 = 0.005027 m². At 40 MPa, theoretical push force is about 201 kN. If a plant applies a hypothetical 0.85 system factor for its measured losses, its planning value becomes about 171 kN. That factor is not a SIMITCH rating; the installed machine must establish its own correlation.

“Treat nominal force as an input to system verification, not as a guarantee at the workpiece. The drive, line, cylinder, tooling, and controls all influence the installed result.”

When a Split Layout Fits—and When It Does Not

Split layouts fit when the tool area is tight but a remote location can safely house the drive, valves, and service points. They are weaker choices when the process needs high force through most of a long stroke, the hydraulic line cannot be protected, or external guidance cannot keep the load axial.

When should you not buy a split-type cylinder?

Do not treat a split system as the default when remote packaging has no clear benefit. Integrated boosters can reduce external hydraulic interfaces in some layouts. Conventional hydraulic systems may fit better when high force is needed across long stroke lengths.

When force and motion must be regulated continuously, or the plant already supports hydraulic power and maintenance, a conventional hydraulic system may also be a better fit.

Buying a split arrangement is premature while tool guidance, energy isolation, hose protection, or workpiece acceptance remain undefined. Those are design inputs, not installation details to solve after delivery. Next comes an interface review, not a larger cylinder.

Match the Circuit Before You Match a Model

Circuit matching starts with force at a stated pressure, usable oil volume, the approach–power–return travel profile, cycle time, dwell, and recovery. Model selection comes later. All working-cylinder, drive-unit, valve, port, line-route, sensor, and tooling decisions must support the same motion and load sequence.

Begin with the force window, not a single maximum. Record the minimum force that produces an accepted part and the upper limit that protects the tool, workpiece, and frame. Then specify where the power stroke begins, how much high-force travel is needed, how long the dwell lasts, and what retraction force or spring force must be overcome.

Next, connect pressure to the actual piston area. Head-end area determines theoretical push force; the cylinder rod end has a smaller effective annular area, so pull or retraction force is different. Friction, pressure loss, opposing load, seal condition, tool geometry, and frame deflection reduce the result available at the process.

For exact family data and the engineering handoff, use the split-type pneumohydraulic working cylinder specifications. Keeping model tables on that page gives the commercial page one clear job while this guide answers implementation questions.

Pressure must stay beside every commercial force value. The current page lists the AT family at 13–1030 kN under a 400 bar basis and the HZ family at 48–492 kN under a 250 bar basis. Those four figures belong to the family shortlist; installed acceptance still comes from the completed machine.

What information is needed before selecting a working cylinder?

Provide the accepted process force window, approach travel, high-force stroke, return travel, cycle time, dwell, plant air under dynamic load, mounting envelope, hose route, external guidance, sensor plan, control sequence, tool deflection, safety concept, and workpiece acceptance method. Missing inputs should be marked open, not replaced with assumptions. The same data lets a supplier separate approach travel, power-stroke oil volume, return demand, sensing, and acceptance criteria before proposing a model or accessory package.

Selection scenario. One team asks for a 120 mm stroke because that is the distance from the home position to the part. Drawing review shows that only the final 6 mm needs high force; the preceding 114 mm is approach travel. That distinction changes the circuit discussion. Usable oil volume, transition point, drive recovery, and sensor sequence must be checked against a 4.2 s target cycle and a 0.6 s dwell. Ordering from the 120 mm number alone could produce a cylinder that fits mechanically but cannot repeat the required power-stroke timing. Afterward, the corrected RFQ separates all three travel phases and attaches the timing diagram.

Mounting, Hose Routing, and Tool Guidance

Mounting must keep cylinder force axial, while an external guide carries side load and tool reaction. Hose routing must protect the hydraulic line from tight bends, abrasion, heat, moving pinch points, and unsupported fittings. Service access must allow safe inspection, measurement, and approved bleeding without entering an energized hazard zone.

Before startup, compare the released drawing with the physical machine. Check the mounting face, fastener strategy, rod-end connection, tool guidance, hard stops, line restraint, bend condition, fitting orientation, sensor targets, bleed access, and the zero-energy service position. Photograph any deviation and close it through the change process before the first loaded cycle.

This walkdown also checks that the cylinder cap, cylinder barrel, rod end, and inlet and outlet ports remain accessible under the planned guard arrangement. Access does not mean a technician may work while energized; it means the approved isolation and verification procedure can be executed without dismantling unrelated machine sections.

A 10-Cycle Commissioning Protocol

Called the 10-Cycle Commissioning Card, this protocol turns a successful first stroke into repeatable evidence. It checks the released build, safe low-risk motion, pressure transition, stroke and dwell, dynamic air, hydraulic response, return, workpiece result, leakage, and recovery across ten representative cycles using plant-specific acceptance limits.

1. Verify the release — match the drawing, cylinder, drive, line, fittings, sensors, guards, and energy-control procedure.
2. Check the isolated state — perform fill, precharge, and inspection tasks only under the approved machine procedure.
3. Prove low-risk movement — confirm direction, stops, sensor order, and clearance without a representative process load.
4. Set the approach — verify approach speed and the transition position without masking impact or tool contact.
5. Observe the power stroke — record dynamic air, hydraulic rise, stroke, dwell, and control timing together.
6. Run ten representative cycles — use the same workpiece, tooling, settings, and measurement method for the sample.
7. Release against the process — accept only when machine safety and workpiece criteria both pass.

Blank fields are intentional. Responsible plant personnel supply the released limits, calibrated instruments, sampling method, and part-acceptance criteria. Ten cycles are a commissioning screen, not a statistical capability study.

Formatting example only. A hypothetical record might show dynamic air changing from 6.0 bar to 5.6 bar, hydraulic peak from 250 bar to 248 bar, power stroke from 6.0 mm to 5.9 mm, cycle time from 4.2 s to 4.9 s, and dwell from 0.60 s to 0.58 s. Another project could use 7.0 bar, 400 bar, 12 mm, 3.8 s, and 0.40 s. None of these values is a recommendation; the point is to keep units, measurement locations, and cycle identity attached to every entry.

Instrument records should also state resolution and range. Formatting examples include 0.1 bar, 1 bar, 0.1 mm, 0.01 s, 0.1 kN, 1 MPa, 1 °C, 5 ms, 10 ms, and 0.5 %; actual requirements come from the plant measurement plan and selected hardware.

Commissioning scenario. Three unloaded cycles return cleanly, so the team adds the representative tool and part. Cycle 1 reaches the planned pressure, but Cycle 6 takes 0.7 s longer and the dynamic machine-inlet air trace dips at the start of the power stroke. Hydraulic peak remains close to target. That pattern directs the team upstream before anyone changes the cylinder. They inspect the local regulator, valve flow path, and supply restriction, then repeat the complete 10-cycle card after correction. Release uses the new cycle set; those early successful strokes remain diagnostic evidence, not proof of acceptance.

Troubleshoot by Measured Node, Not by Guessing

Our Symptom-to-Measurement Triage Matrix starts at the first abnormal signal and moves one node upstream or downstream. This method separates air-supply, valve, drive, line, cylinder, tooling, and control faults before parts are removed. It also keeps live-line loosening and guard bypass out of the diagnostic routine.

Useful diagnostic notes record the symptom, cycle number, command state, pressure point, position, workpiece result, and what changed from the released baseline. “Cylinder weak” is not a diagnosis. “Cylinder-side pressure matched baseline, but tool position stopped 1.8 mm early after contact” is a useful branch point.

Maintenance and the Zero-Energy Boundary

Maintenance starts with a machine-specific zero-energy boundary, not a stopped piston. Isolate pneumatic, hydraulic, electrical, mechanical, and gravity hazards; dissipate or restrain stored energy; then verify isolation under the site’s authorized procedure. Stop buttons, interlocks, and PLC indications are control information, not energy-isolating devices.

OSHA’s typical lockout/tagout procedure specifically addresses stored or residual hydraulic and pneumatic energy and requires verification before work. Its energy-control circuitry guidance also explains why control circuits cannot replace energy isolation.

System designers should review both ISO 4413 for hydraulic fluid power and ISO 4414 for pneumatic fluid power in the context of the complete machine. These standards do not turn a component into a certified machine. Risk assessment, controls, guards, instructions, and validation remain project responsibilities.

Routine work can then be organized by condition and duty: inspect hoses and fittings for damage or leakage; review mounting and external guidance; compare sensor timing with the baseline; check contamination or aeration clues; verify that the line remains restrained and protected; and trend cycle or pressure changes. Use the component instructions and the plant’s environment to set intervals. Any universal “every 500 hours” claim would be guesswork without duty and contamination data.

Point-of-operation safety is separate from energy isolation. OSHA’s machine-guarding rule requires protection appropriate to the hazard. Cylinder selection cannot replace the guard, safety function, or validation for the assembled machine.

Prepare the Engineering Handoff

Effective engineering handoffs give the supplier and machine builder one controlled set of process, motion, utility, layout, guidance, sensing, safety, and acceptance inputs. Each handoff should identify owners and open questions, so a missing limit is resolved by test or design review rather than hidden inside a model assumption.

Send that package for an AT and HZ configuration review. Readers evaluating the supplier can also review SIMITCH manufacturing and application-engineering background before the project discussion.

Frequently Asked Questions

These answers cover the operating and integration questions that sit around the commercial AT/HZ selection page. They are intentionally general because actual force, stroke, pressure, port, line, duty, and safety decisions depend on the selected components and the assembled machine.

References & Sources

Load-bearing technical and safety statements in this guide use first-party product documentation and primary standards or government sources. Commercial competitor pages were reviewed for content gaps but are not used as evidence.

1. SIMITCH — Split-Type Pneumohydraulic Working Cylinders, AT & HZ Series
2. ISO 4413 — Hydraulic fluid power: General rules and safety requirements
3. ISO 4414 — Pneumatic fluid power: General rules and safety requirements
4. OSHA 1910.147 Appendix A — Typical minimal lockout procedure
5. OSHA — Energy control circuitry prohibition
6. OSHA 1910.212 — General requirements for all machines

Engineering note: examples in this article illustrate a method, not a product rating or machine-safety approval. Final selection and validation must use the released component documentation and the assembled machine’s risk assessment, measurements, and acceptance plan.