Telescopic Hydraulic Cylinder Basics

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telescopic hydraulic cylinder

Hydraulic cylinders are an unavoidable part of every hydraulic system. The work done by the hydraulic cylinder due to the applied hydraulic fluid pressure s what makes most of the systems work.  We can find different varieties of hydraulic cylinders in the market. They differ based on construction, design, application, fluid compatibility, and other parameters. This article focus on one such hydraulic cylinder called telescopic hydraulic cylinder also known as multi-stage cylinders.

Unlike the welded rod cylinders, where the barrel is directly welded to the end caps and ports to the barrel, the telescopic hydraulic cylinders are linear actuators with sleeves or stages. Sleeves or stages means that the design contains a series of four or five tubular rods that are nested inside another. The diameter of these tubular rods decreases sequentially in such a way that it fits perfectly inside the other rod and to extends when pressure applied. This construction feature enables it to be used with applications that require a long forward stroke such as trucks, trailers, and similar agricultural and construction machinery. 

The major benefits of the telescopic hydraulic cylinder are compact size, long-stroke capability, and ability to meet angle requirements. The sleeves or stages of this cylinder are nested inside one another and it extends when the hydraulic pressure is applied and retracts to the original compact position when work is completed. This feature makes the hydraulic system compact and user-friendly. Similarly, in applications in dump trucks, for smoothly releasing materials from the truck, it is necessary to maintain specific angles. In such situations, telescopic hydraulic cylinders are most favorable. The drawbacks of the telescopic hydraulic cylinder are complex design and more expensive.

Telescopic Hydraulic Cylinder Construction and Working 

As discussed, the telescopic hydraulic cylinder has sleeves or stages. In the design, each ram except the smallest and last one will be hollow. The main telescopic cylinder with the largest diameter is called barrel and the one with the smallest diameter is called a plunger. Each of the remaining tubular rods is termed as stage or sleeve in general. During hydraulic system operation, when the hydraulic fluid is pumped to a telescopic cylinder, the barrel(one with larger diameter) will extends first and when it reaches its maximum stroke, the next stage will extend and this operation proceeds till the plunger(stage with the smallest diameter). 

Single-acting cylinders and double-acting cylinders are the two different types of the telescopic hydraulic cylinder. In single-acting cylinders, the cylinder extends with the applied hydraulic pressure and for retraction, it requires additional mechanism or gravity. Whereas, in the double-acting telescopic cylinder, hydraulic force is required for both extension and retraction.

Telescopic Hydraulic Cylinder Testing

Telescopic cylinders are complex in construction and it is necessary to properly test the cylinder before its installation. Pressurized fluid passes through the cylinder and it can be dangerous if it leaks. Also, the primary operation involved in the hydraulic cylinder is its extension and retraction. If the operation is not smooth enough, then the result will be a complete failure of your hydraulic system. So, the best method for testing the telescopic cylinder is by pressurizing the cylinder to its maximum. Vertical cylinder tester is a type of telescopic hydraulic cylinder testing that can bleed air out from the multi-stage cylinder. The test procedure starts by securing the cylinder and then pressurizing it to the maximum limit(till all the tubular rods fully extend). Once the cylinder is fully pressurized, the reading on the gauge will be noted in a timely manner. There will be a change in pressure reading when the cylinder indicates any failure.

During cylinder testing or installation, the technician or other professionals need to be more cautious. Because of that, they are advised to follow all the rules mentioned for worksite safety.

Also Read : Hydraulic Cylinder

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