HOW TO CHOOSE THE CORRECT HYDRAULIC CYLINDER

In the world of industry and manufacturing, many machines and applications require a pushing / pulling force in a straight line or arc. For this purpose, we often use hydraulic cylinders, which serve as the muscles of our machinery and equipment. 

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The hydraulic cylinder is a piston and rod assembly inside a cylindrical bore, actuated by the flow and pressure of hydraulic fluid with the output of linear motion and mechanical force. 

We find hydraulic cylinders in industrial machines like presses, jacks and plastic moulding equipment, as well as mobile equipment like excavators and mining trucks.

Hydraulic cylinders are useful in their simplicity, durability and significant power density. 

A Few Basic Cylinder Types

Tie Rod Cylinders

Made of high strength steel, often seen in automotive manufacturing and general industrial applications. 

Welded Or Mill Type Cylinders

Originally designed for use in steel mills, foundries, and other heavy-duty jobs such as civil engineering and marine applications in harsh environments with wide temperature ranges.

Rams

These are single-acting cylinders used for pushing applications such as heavy-duty presses and hydraulic jacks. 

Factors To Consider For Cylinder Selection

Cylinder Dimensions

• Bore size
• Rod size
• Stroke length

These measurements are mainly based on the size of the load to be moved, and the available system pressure, or operating pressure. Common operating pressures range from 500 to psi. 

We first calculate the mass of the load to be moved. Once we know the mass, we can figure out the force required to move it. This will depend on the friction and acceleration factors of our specific application. In the calculation of our force requirement, we must always include a buffer to allow for a margin of error. 

Bore Size

Once we know our force requirements, we can calculate the bore size requirement:

Load to be moved (pounds) / Operating pressure (psi) = Area (square inches)

By converting the area to a diameter, we can determine the bore size of the cylinder required to move the load. 

To account for system losses, one should generally size the cylinder at 15 – 20% above the load requirement. 

Rod Selection Recommendations

Our next step is to select an appropriate rod size. 

Piston rod diameter is critical. An underspecified piston rod makes the cylinder more prone to stress, wear, and failure. 

To select an appropriate rod size, we must know the length of the stroke. For cylinders with long strokes, a fully extended rod can buckle under its own weight. Rod deflection should never exceed 1 to 2 mm.

Here at Kappa Engineering, we use software to calculate rod buckling strengths for given rod sizes and use the data to make suitable recommendations for given loads. 

• Standard rod options: For a given bore, only use the smaller rod for short-stroke push loading or reduced pressure applications. Use the larger rod to obtain maximum reliability and lifetime. 
• If the required rod diameter exceeds that of the largest available, one should reconsider design parameters or look into a custom made cylinder. 

Geometry Of The Installation

Once we know the nature of the load, we then need to consider the geometry involved in moving it. The structure of the machine or installation will determine the type of mount to be used. 

For a machine such as a ‘jack’ or a ‘press’, the actuation is directly up and down. For some other machines, the centre of the load is not centred at perpendicular angles to the point of lift force, and the cylinder force requirement changes.

Mounting plays an important role in performance and the main factor is whether the cylinder body is stationary or pivots. 

Fixed Mount options are best for straight-line force transfer and minimal wear, they include:

• Centreline mount
• Flange mount
• Side mount

The fixed mount is easy to install and service, but has little tolerance for misalignment and so must be well guided. 

Pivot Mount options absorb force on the cylinder centreline and allow for one plane of rotation. They generally include:

• Clevis mount
• Trunnion mount
• Spherical-bearing mount

The pivot mount is applicable wherever the cylinder needs to change alignment during motion.

Seals

Seals are a vulnerable aspect of the hydraulic system. Choosing the correct seal will increase cylinder life and prevent fluid leakage. To choose the correct seal we must understand the cylinder operating conditions and temperatures, as well as the type of hydraulic fluid used. 

Polyurethane seals – Most standard applications – flexibility, strength and wear resistance.

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Teflon seals – Highly dynamic applications and systems requiring low friction.

Buna-N(Nitrile) seals – Cylinders using water, or water-glycol based fluids.

Fluorocarbon seals – Systems using synthetic fluids and or high temperature operating environments. 

Cushions

Depending on your application, cushions at the end of the cylinder stroke may be required. Cushions are recommended to decelerate high-speed rods and buffer the impact of the piston assembly on the cylinder end cap. Cushions are optional and do not affect the cylinder envelope or mounting dimensions. 

Other options to prevent impact loads are external mechanical stops or proportional valve technology. 

We hope that this information was helpful as an introduction to choosing the correct solutions for your cylinder requirements. 

At Kappa Engineering, our technical capacity and strategic partnerships enable us to repair and manufacture any size and quantity of hydraulic cylinders. We have a dedicated repairs department that ensures minimal downtime.  Our advanced quality control system is TUV certified ISO : to make sure our newly manufactured products and repairs conform to the highest standards. 

Hydraulic cylinders have many applications in the hydraulic industry. Most of the time, the cylinder performs work by converting the energy into fluids. The mode of conversion leads to many types of hydraulic cylinders. Find below the most common types of hydraulic cylinders you can buy.

1. Single Acting Cylinders

A single-acting cylinder has a port that works in one direction only. When a liquid or a gas enters the cylinder barrel, the rod will increase in size. For the rod to return to its initial state, the cylinder may use an external force or a load string. An example of single-acting hydraulic cylinders is the hydraulic jack used in the auto industry.

2. Double Acting Cylinders

A double-acting cylinder's ports are on both the rod and head parts. This design enables the hydraulic cylinder to move fluids more efficiently. The ports at both ends will control the movement of fluids within the cylinder. Hence, liquids and gases in double-acting cylinders can flow in two directions.

For example, if a liquid in the cylinder moves towards the rod section, the piston rod will shrink. In contrast, the piston rod will increase in size when the fluid flows toward the head section. The ability of the liquid to move in two directions means that a double-acting hydraulic cylinder can help to raise and lower equipment.

3. Nested Cylinders

The possible applications of hydraulic systems have significantly increased, and manufacturers are trying to develop more special designs. One of the latest designs involves putting together at least three cylinders. The combination of many cylinders creates a system with varying forces and speeds. Hence, hydraulic cylinders can do many things during a single stroke.

4. Rotating Cylinder

All the cylinders above don't rotate, which may limit their applications in many industries. That is why some manufacturers produce the rotating cylinder type with linear motion. The rotating cylinder design resembles that of a non-rotating cylinder in most aspects. The main difference is that the rotating cylinder contains a distributor component that can provide fluids to the rod and head ends of the cylinder. In addition, the rotating cylinder includes passages to allow the inflow of oil on both sections of the cylinder.

5. Low Height Cylinders

Low-height hydraulic cylinders may be ideal if you have limited space or want to move the cylinder around. The low-height cylinders have the exact working mechanism as many of the cylinders listed above but are lighter and smaller. However, you are only likely to find this type of cylinder in the single-acting model. Also, you can't use the low-acting hydraulic cylinder to perform activities requiring tremendous force.

6. High Tonnage Cylinders

Get a high-tonnage cylinder if your projects require a heavy lifting force. These cylinders can lift very heavy items that weigh over 1,000 tonnes. You can also use the high-tonnage cylinders for stability and protection for your loads. Hydraulic cylinders may use double-acting or single-acting working mechanisms.

7. Tie-Rod Cylinders

The tie-rod cylinder has a threaded steel rod to stabilize the components of the hydraulic cylinder. These cylinders also come with end caps to block fluid leaks. Hence, these cylinders have many applications in the industrial and manufacturing sectors. Those who buy tie-rod cylinders can expect easy repair, assembly, and maintenance of the cylinders. 

Using Cylinders

Hydraulic cylinders are available in multiple models and styles. Your choice of a hydraulic cylinder will depend on your needs and budget. For the best hydraulic cylinders, reach out to Quad Fluid Dynamics, Inc. 

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