Telescoping Cylinders

Custom Designed Telescopic Hydraulic Cylinders

Hyco Canada designs and manufactures both Single Acting and Double Acting Telescopic Cylinders. We specialize in large bore custom designed cylinders.

We also have a series of Standard Catalogued Telescoping Cylinders . These standard models range from 7 ton to 50 ton capacities and stroke lengths up to 343 inches ( 28.6 feet).

Our Custom Designed Telescopic Cylinders, however, are available in an infinite variety of bore sizes and mounting configurations. We have built special units up to 28" in diameter and 600 inches in stroke. These actuators are used in highly demanding service applications around the world including oil field drilling rigs and large capacity marine cranes.

Above: Hyco Telescopic Cylinders are used in rugged oil field applications.

The advantage of telescopic cylinders is that they extend to an overall length that is longer than their retracted length. In fact, 5 or 6 stage telescopic cylinders will have an extended length many times longer than the collapsed length.

A conventional single stage rod cylinder in comparison has a stroke that is less than its retracted length. Typically a rear pivot mount rod cylinder with a 12 inch stroke will have an overall length retracted of at least 20 inches.

While telescoping cylinders have this remarkable extended length to retracted length ratio, their use has certain procedures and design considerations that must be followed in order to ensure a long, safe, trouble free service life. This is even more critical in the case of double acting telescopic cylinders.

Design Considerations with Telescoping Cylinders

Hydraulic cylinders must be used in a way that avoids side loads from pushing on the actuator. Side loads will cause excessive wear and a decreased service life. In extreme cases, a catastrophic failure could occur such as when the cylinder buckles in service.

This is even more critical in the use of telescoping cylinders. The long extended body length of a telescoping cylinder makes them very susceptible to side forces.

Above: Hyco Telescopic Cylinders erect the mast of a Mobile Drilling Rig.

For this reason, a telescoping actuator must only be used as a force generating device and never as a stabilizing structural component. They are the muscles of a machine, not the bones.

A telescoping cylinder should therefore be allowed to float in its mountings so as to enable proper alignment with the load. Cylinder pivot pins less than 5 inches in width should have about 1/4 inch clearance per side in the pivot eye hole. Pivot eyes larger than 5 inches width should have a clearance of at least ½ inch per side in the pivot eye hole. These pivot mounts should be regularly lubricated to ensure free movement.

The exposed cylinder sleeves should be protected from external contamination as much as possible so as to preserve the seals. A light film of oil should be visible on the exposed cylinder plungers with the unit extended. A small amount of oil will gather on the cylinder heads over the course of many cycles. This is actually a normal and desired condition. The cylinder should be bled of air regularly (at least weekly).

The hydraulic hoses leading to the actuator should be protected from rubbing, chafing, and kinking as the cylinder moves through its complete cycle extending and retracting. These hoses should be inspected regularly and replaced when worn. A hose failure is one of the most common causes of hydraulic system failure. A hose failure will cause a rapid drop in a raised load and could cause extensive damage to equipment and be very dangerous to personnel.

Above: Telescopic Cylinders are used to raise a dump platform in the pulp and paper industry.

Telescoping cylinders should never be exposed to pressures beyond the maximum recommended operating pressure for the unit as stated by the factory. Excessive pressures may cause the cylinder tubes to bulge out or even split. This will result in the cylinder jamming in service or even suddenly dropping the load at high speed.

Application and Use of Telescoping Hydraulic Cylinders

Telescoping cylinders are often used in mobile equipment such as heavy truck dump bodies and hydraulic cranes. This is rugged and demanding service. A few simple procedures should be followed to maintain safe operation and ensure a long service life.

Above: Two Single Acting Telescopic Cylinders lift a dump body.

Cylinder end mounts should be lubricated regularly to enable them to move freely.

Hydraulic fittings and hoses should be inspected regularly for wear and fatigue. Replace them promptly if a problem is detected. A line failure could cause a sudden drop in the load and endanger personnel.

Air should be bled from the system weekly to ensure smooth operation.

Maintenance on telescoping actuators should only be performed by trained qualified personnel. The actuator should be lowered to the ground or supported to prevent movement before inspecting or performing maintenance. Sufficient personnel and equipment must be on hand to support the equipment when removing an actuator from service.

A dump box must only be lifted with the truck on solid level ground. A tractor trailer unit must be in a straight line and not jack knifed before tilting the dump box. Do not operate the unit in a heavy cross wind or when the box is swaying. If the truck body begins to lean or sway, lower the unit immediately. The telescopic cylinders are not able to withstand the side forces that occur when a dump box is leaning or swaying. An actuator failure may occur or the truck may upset.

Click here to download the Hydraulic Dump Box Safety Bulletin .

Do not operate the dump body with other personnel or equipment alongside. Do not allow personnel under the dump body unless the body is prevented from dropping by external equipment in addition to the cylinder.

Do not leave the controls while the actuator is operating. Do not cause the actuator to jump or jerk as this will cause hydraulic pressure spikes that may damage the telescopic actuator. Feather the control valve to avoid hydraulic pressure spikes.

Completely lower the dump box before moving the truck. Do not jerk or slingshot the truck by moving and then engaging the brakes in order to try to free up a sticking load. This will cause hydraulic pressure spikes that will damage the actuator.

Above: A large bore, multi-stage telescopic cylinder is readied for shipment from Hyco Canada.

Use and Application of Double Acting Telescopic Cylinders

A double acting cylinder extends and retracts using hydraulic pressure both ways. Because of the special porting involved, a double acting telescopic cylinder is much more complex than a single acting telescopic cylinder. In addition, because of the difference in the effective piston areas on extension and retraction, extremely high, damaging pressures can occur if a double acting telescopic cylinder is not operated correctly. Only fully trained personnel should operate a double acting telescopic actuator. With these factors in mind, double acting telescopic actuators have additional operating requirements compared to single acting units.

A double acting telescopic actuator should be fully retracted when not in use.

A double acting telescopic actuator should not be extended until it has been fully retracted. Oil trapped on the retraction side will be captured and subjected to very high pressure intensification causing seal failure or a cylinder sleeve to bulge. This can happen if the unit has been partially extended and then the pressure relieved.

Do not operate a telescopic actuator if the load being pushed is misaligned. Misalignment will cause side forces on the actuator that will cause excessive wear and even buckle the unit.

A new unit should be fully extended and retracted about 10 times without a load in order to bleed the actuator of entrapped air. Check that the stages are sequencing in the proper order. The largest stage should move first, then the next largest, and so on. On retraction, the smallest stage should retract first, then the next larger stage, and so on.

If when operating a load, such as on a Roll Off unit, the cylinder is pulled open by a heavy load, a column of air will form inside the actuator. If then the container goes over center and now compresses the actuator, a large pressure spike may occur as the cylinders close and suddenly hit the internal column of oil. To prevent this, the actuator should be extended with the control valve in order to completely fill them with oil before pulling the container further onto the Roll Off unit.

Above: 6 new telescopic cylinders ready to ship from Hyco Canada

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