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A Synopsis Of Hydraulic Cylinders

An actuation device that makes use of a pressurized hydraulic fluid is known as a hydraulic pump. This mechanism is used for producing in linear motion and force in applications that transfer power.

In Insight Into Hydraulic Cylinders

What Are Hydraulic Cylinders?

An actuation device that makes use of a pressurized hydraulic fluid is known as a hydraulic pump.

This mechanism is used for producing linear motion and force in applications that transfer power. In other words, a hydraulic cylinder converts the energy stored in the hydraulic fluid into a force used to move the cylinder in a linear direction.

Operation Of A Hydraulic Cylinder:

The hydraulic pressure in these cylinders is in the form of hydraulic fuels that are stored under pressure in these cylinders. The energy stored in these oils is converted into motion. In a complete hydraulic system, a hydraulic motor consists of one or more hydraulic cylinders. A pump regulates the oil-flow in the hydraulic system. The pump is a part of the generator of a hydraulic system. The hydraulic cylinders initiate the pressure of the oil, which cannot be more than that required by the load.

A hydraulic cylinder consists of a cylindrical barrel, piston, and a piston rod. The piston that is placed within the barrel is connected to the piston rod. The cylinder bottom, and the cylinder head, closes the bottom and the head of the barrel respectively. The cylinder head is the side from where the piston rod exits the cylinder.

Hydraulic CylindersThe cylinder bottom and the piston rod are mounted with mounting brackets or clevises. The piston in the hydraulic cylinder consists of sliding rings and seals. The piston rod chamber and the bottom chamber are the two chambers within the cylinder.

The piston rod starts moving outwards, as the hydraulic fluid is pumped into the bottom side of the hydraulic cylinder. In the reverse process, the hydraulic fluid is pushed back into the reservoir by the piston. The pressure in the cylinder is the ratio of unit force per unit piston area.

The pressure generated in the piston rod chamber is the ratio of the unit load per the difference in the unit piston area and unit piston rod area. This calculation is used when the hydraulic fluid is let into the piston rod chamber as well as the fluid flows smoothly (without pressure) from the piston area to the reservoir. In this way, the expansion and retraction (push and pull) action of the hydraulic cylinder is generated.

Classification Of Hydraulic Cylinders According To Function:

Single Acting Cylinders:

In single acting cylinders the fluid is pressurized from only one side of the cylinder during both the expansion as well as the retraction process. A spring or an external load is used to return the cylinder top to its original position i.e. when pressure of the fluid is cut off.

Double Acting Cylinders

In the double acting cylinders, the pressure from the fluid is applied in both the directions. Single cylinders that consist of springs are not used in large stroke applications because there are inherent mechanical problems associated with the spring. The double acting rods could be of two types:

•  Single rod ended

•  Double rod ended

Classification Of Cylinders According To Specifications:

Plunger Cylinders:

These cylinders are also known as Ram cylinders. These types of hydraulic cylinders are placed in an upright position. This is done so that once the supply of the fluid is stopped, the weight on the cylinder will make it return to its original position. The cylinders used in automobile service centers are a good example of the plunger cylinders.

Telescoping Cylinders

Telescopic cylinders are also known as multistage hydraulic cylinders. These cylinders have at the most six stages. These are specially used in applications where there is less area. Telescopic cylinders can either be single action or double action. The stroke of these cylinders is long and is used in applications such as cranes and forklifts, etc.

Cable Cylinders

The cable cylinders can either be hydraulic or pneumatic powered cylinders that are of the double acting type. These cylinders have long strokes and produce moderate force. The cable cylinders can be operated in limited space.

Diaphragm Cylinders

Diaphragm cylinders are of two types i.e. flat diaphragm and rolling diaphragm. These cylinders have zero leak around the piston.


Components of A Hydraulic Cylinder:

There are various components that form a part of the hydraulic cylinders.

The various parts are the cylinder bottom, cylinder bottom connection cylinder barrel, and cylinder head. It also consists of the piston, piston rod, and the piston rod connection. And some of the hydraulic cylinders may comprise of the feet. These are used to mount the barrels.

The cylinder barrel is a thick tube that has to be machined from the inside. The interior of the barrel is honed or ground and in some cases both. The cylinder barrel and the bottom of the cylinder are welded together in most of the hydraulic cylinders.

This welding of the bottom of the cylinder to the barrel can damage the interior of the barrel. Hence, it is preferred to have the two screwed together. This type of connection will be helpful during repairs or maintenance of the cylinder barrel. On the other hand, the barrel is connected to the cylinder head with a lock.

There is a simple lock system used for a simple cylinder. In most of the hydraulic cylinders the flanged or screwed connections are used. The best type of connections and most expensive connections are the flanged connections. It is considered to be the best type of connection because before machining a flange is welded onto the tube.

The other positive aspects are that the flange is always bolted and can be removed easily when required. The disconnection process as well as the alignment process while mounting is much tougher for the bigger hydraulic cylinders. This problem in particular arises where the screw size is between 300 mm to 600 mm.

There should be no bending moments implied on the hydraulic cylinder as they are applied in expansion and retraction actions. The single clevis connection with a ball bearing is considered to be the most appropriate connection, as all the above-mentioned problems do not arise.

Specifications To Be Considered While Purchasing A Hydraulic Cylinder:

The specifications that need to be considered while purchasing a hydraulic cylinder are:

•  Bore Diameter: It is the diameter of the cylinder bore.

•  Maximum operating pressure: The maximum working pressure a cylinder can carry is known as maximum operating pressure.

•  Rod Diameter: It is the diameter of the piston or the rod that are used in hydraulic cylinders.

•  Stroke: The distance traveled by a piston in a hydraulic cylinder is known as stroke. The length of a stroke could be several feet, or a fraction of an inch.

•  Type Of Cylinder: The different types of cylinders are tie-rod cylinder, ram cylinder and welded cylinder.

Tie-rod cylinder: These types of hydraulic cylinders make use of a single or multiple tie-rods to provide extra stability to the cylinder.   The tie-rods are mostly installed on the exterior diameter of the cylinder. The tie-rods carry most of the load in this type of hydraulic cylinder.

Welded cylinder: There are heavy-duty welded cylinders used to balance the cylinder. The welded cylinders are smooth hydraulic cylinders.

Ram cylinders: As the name suggests, this cylinders act as a ram.   The cross-section of the moving components is half of the cross-section area of the piston rod.   These hydraulic ram cylinders are not used to push and are mostly used to pull. The ram cylinder is a hydraulic cylinder that is used in applications of high pressure.

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