The OMCN single-acting hollow plunger hydraulic cylinders are designed for industrial applications where a simple front pushing force is not sufficient and where a threaded rod, tie rod or pulling element must pass through the cylinder axis. The central bore passes through both the cylinder body and the piston, allowing the cylinder to be used in pulling, extraction, tensioning, straightening and controlled assembly operations.

This configuration is mainly selected when a component cannot be pushed directly or when a press-fit part must be removed without damaging seats, surfaces or adjacent components. The cylinders are normally used with threaded puller rods, reaction nuts, bridge plates, bearing separators, pulling sleeves, flanges and dedicated accessories suited to the application. The threaded rod passes through the central bore and connects to the component to be extracted or tensioned; hydraulic pressure moves the annular piston and transfers the required force along the working axis.

The cylinders are single acting, meaning that hydraulic pressure generates the active piston stroke, while a built-in return spring retracts the piston when the pressure is released. This system makes the cylinders practical and fast to use, especially in operations where the ram must automatically return to its initial position after extraction, pulling or pressing. Spring return also reduces the time required between one operation and the next, particularly in repetitive maintenance work or industrial assembly operations where the equipment must be repositioned frequently.

The maximum operating pressure is 700 bar, a standard value for high-pressure hydraulic systems used in workshops, industrial maintenance, heavy fabrication, infrastructure work, energy plants and mechanical assembly operations. For correct operation, the cylinder must only be connected to pumps, hoses, quick couplers, pressure gauges and valves rated for at least 700 bar. A pump with a controlled release valve is recommended, while a pressure gauge is particularly useful in sensitive applications to monitor the actual pressure applied to the system.

The main advantage of the hollow plunger is the ability to perform pulling operations using a compact and concentric system. In a typical bearing removal application, for example, a threaded puller rod passes through the central bore of the cylinder and is connected to a bearing separator or puller positioned behind the bearing. The cylinder reacts against a bridge plate or rigid structure; when the pump is operated, the piston generates the force required to pull the component along its axis. The same principle can be used for removing bushes, pins, pulleys, couplings, shafts, taper pins, railway components, transmission parts and interference-fitted mechanical assemblies.

For tensioning applications, the cylinders are used with through rods, nuts and reaction plates to apply controlled force to large-diameter bolting, steel structures, flanges, industrial equipment and mechanical joints subjected to high loads. In these applications, the central bore keeps the puller rod aligned with the cylinder, improving load distribution and reducing the risk of side loading. The cylinders may also be used for controlled straightening of metal elements, positioning of structures, recovery of seized components and alignment of mechanical parts during installation or maintenance.

The correct model should be selected according to the required push or pull capacity, stroke length, useful bore diameter, available installation space and oil volume required by the cylinder. The range includes capacities of 12 ton, 24 ton and 37 ton, with strokes approximately ranging from 8 mm to 150 mm and oil capacities from 15 cm³ to 471 cm³. Compact versions are suitable for clamping, limited pulling work, short extraction operations or work in restricted areas. Long-stroke versions are better suited to deep extraction, removal of long components, tensioning operations with greater axial travel and applications requiring a larger operating distance.

Oil volume is a key factor when selecting the pump. A cylinder with a low oil capacity, such as 15 cm³ or 56.4 cm³, can be operated quickly using a compact manual pump because only a limited number of pumping strokes are needed to complete the movement. A cylinder with a higher capacity, such as 360 cm³ or 471 cm³, requires a larger quantity of oil and more manual pumping cycles; in these cases, a two-speed hand pump, air-hydraulic pump or electric hydraulic power pack can be more efficient, especially for repetitive work or reduced cycle times. The pump reservoir capacity must always exceed the cylinder oil requirement while maintaining a suitable operating margin.

Cylinder selection should never be based on nominal capacity alone. Required force must take into account friction, corrosion, assembly interference, component geometry, misalignment and an appropriate safety factor. For corroded parts, very tight fits or applications with high breakaway resistance, a higher-capacity cylinder may be necessary compared with the theoretical calculated force. However, excessive force should not be applied without control, as it can deform the part, damage the seating surfaces, break the puller rod or overload the extraction accessories.

During operation, the cylinder must always remain aligned with both the puller rod and the component being moved. Side loads, angled rods, uneven supports or reaction plates that are not sufficiently rigid can cause abnormal wear, reduced efficiency, deformation and unsafe operating conditions. Before applying pressure, the cylinder, rod, nuts, washers and accessories must be checked to ensure that they are correctly tightened and dimensioned for the expected load. Reaction surfaces must be clean, flat and sufficiently strong; adapters must be centered and free from excessive play.

For improved performance, pressure should always be applied gradually while checking the alignment of the system and the response of the component. If the part does not move, pressure should not immediately be increased to the maximum limit. It may be necessary to check for mechanical stops, screws, locking pins, circlips, seized threads, corrosion or unexpected assembly conditions. The use of penetrating lubricant, controlled heating of the outer component or appropriate pulling accessories can significantly reduce the required force and improve safety.

These hollow plunger hydraulic cylinders are used in mechanical workshops, steel fabrication, industrial mechanical maintenance, railway applications, energy plants, infrastructure, construction sites, industrial assembly, technical lifting, automotive, marine, steelworks, cement plants, material-processing systems, machine tool maintenance and production plant servicing. They are especially useful when components must be pulled or tensioned without dismantling complete structures, when working space is limited or when force must be applied accurately along a defined axis.

The 12 ton versions are suitable for light and medium extraction tasks, general maintenance, bushes, small bearings, pins and compact mechanical components. The 24 ton versions offer an effective balance between force, stroke and handling and are suitable for more demanding work on shafts, couplings, industrial components and structural assemblies. The 37 ton versions are intended for heavy-duty applications, high-resistance extraction, large tie-rod tensioning, heavy maintenance and work on larger mechanical components.

With pressure up to 700 bar, a through hollow piston, spring return and a selection of capacities, strokes and oil volumes, these hydraulic cylinders provide a versatile technical solution wherever a component must be pulled, extracted, tensioned or moved with controlled force, precision and safety.