How do I choose a hydraulic ram?

Hydraulic cylinders, jacks, or rams. The names vary but whatever you choose to call them the definition is the same. A hydraulic cylinder is a device that harnesses the pressure generated in a hydraulic system to move a load. Due to the wide variety of cylinder options to choose from, you will need to consider your needs carefully when selecting a cylinder for your job. Answering just a few questions will help you to choose the right hydraulic cylinder for your lifting and pulling projects.

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How will the cylinder be used?

Cylinders are versatile products. Not only are they used for lifting and jacking, but also for pulling, pressing, holding, lowering, and clamping. Knowing the application you need a cylinder to perform is your first important step towards making the right decision.

Where is the cylinder being used?

Hydraulic cylinders are used for countless applications. Many job sites involve harsh conditions, whether that being extreme heat, or the rough conditions of a construction site. Cylinders with a nitrocarburized surface treatment have increased corrosion protection. This makes them much more durable and ideal for harsh environments.

How much space is needed?

The question of how much room you have for your cylinder is an important one. You wouldn&#;t choose a cylinder that has a collapsed height of 16.5cm (6.5 in) for a space that only has 12.7cm (5 in). There are purpose-designed cylinders made for jobs in confined spaces. These go by the name of low-height cylinders, or pancake cylinders.

What stroke is required?

Related to the maximum collapsed height, is the stroke length required. Stroke is defined as the difference between the fully extended height and the fully retracted height of the cylinder. It&#;s the distance between the top of the plunger piston and the bottom of the stop ring. For jobs that need extra stroke, there are telescopic hydraulic cylinders including low-height versions. The stroke determines how far the cylinder will lift, push, pull, or move your load. When considering the stroke of a cylinder, you should keep within 80% of the maximum stroke. This helps ensure better stability and damage from sideload.

How much accuracy and control is needed?

Hydraulic cylinders are available in single acting and double-acting configurations. A single-acting cylinder uses hydraulic pressure to extend the plunger and a return spring to bring it back to the original position. A double-acting cylinder uses hydraulic force to both lift and lower the plunger. This provides much more control and precision.

Is load holding needed?

If your load needs holding in place while you perform your job, a cylinder with load holding is a safe choice. Cylinders that hold your load, eliminate the time-consuming process of cribbing. There are two different types of cylinders that can be used for load holding. Locknut cylinders which utilize mechanical support, and cylinders with check valves.

How heavy is the load?

Each hydraulic cylinder is built to lift a certain capacity. There are general-purpose designs, which are your &#;basic&#; options, and also high tonnage cylinders that have a capacity of up to tons. Like cylinder stroke, the 80% rule also applies to tonnage. Manufacturers always list their maximum weight capacity as a safe limit. However, good practice with cylinders encourages users to only go to 80% of the manufacturer&#;s limit.

Steel or Aluminium Cylinders?

If you&#;re looking for a cylinder for regular use, you will need one that&#;s built to last. Steel cylinders are inherently stronger than their aluminium counterparts. However, if weight is an issue, aluminium cylinders are also robust and much easier for a person to lift, transport, and reposition.

Does the application require mounting?

Some jobs need extra stability or precise cylinder positioning. If your job falls under that category you will need a hydraulic cylinder with either mounting holes or collar threads. Mounting holes are located on the bottom of the cylinder&#;s base and can be attached to a base plate.

How many lifting points are required?

For many larger lifts, you may need more than one cylinder. If that is the case, you will need to select a pump with the appropriate oil capacity. You may also want to think about a synchronized lifting system. A synchronized lifting system will ensure your load&#;s weight is distributed evenly.

Do I need it to pull as well as push?

A hollow plunger hydraulic cylinder design allows for both pull and push forces. This is achieved thanks to a threaded collar for attaching suitable fixing rods.

How level will the contact point be with the saddle?

In many lifting projects, sometimes it is difficult to achieve sufficient contact between the saddle and the load. When this happens there is the risk of damage to the cylinder from side loading &#; often with the user completely unaware it is happening. A greater contact area can be achieved using Tilt Saddles. These are an option that can be specified to work with a wide range of cylinders and help extend the life of the cylinders.

What hydraulic pressure do you need?

Ok so you&#;ve answered the questions above and have a cylinder in mind. Good job! But before making your final selection, don&#;t forget to check whether the hydraulic pressure from your pump will be sufficient. If you need an upgrade there&#;s many great pumps to choose from. For example, plugin manual, electric, battery, air over hydraulic, and lightweight models for working at height.

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Summary

Keep these things in mind when looking for a cylinder and you will come away with the best option for your application. If you have any more questions about how to choose the right cylinder, you can easily get in contact with your local Enerpac territory manager or distributor here.

Here&#;s a checklist to summarize;

• How will the cylinder be used?
• Where is the cylinder being used?
• How much space is needed?
• What stroke is required?
• How much accuracy and control is needed?
• Is load holding needed?
• How heavy is the load?
• Steel or Aluminium Cylinders?
• Does the application require mounting?
• How many lifting points are required?
• Will I need it to pull as well as push?
• How level is the contact point with the saddle?
• What hydraulic pressure do you need?

In this hydraulic selection guide, we&#;ll point out the different factors you need to consider in order to select the right hydraulic cylinder for any specific application.

A hydraulic cylinder is a linear actuator engineered to create either a pushing or pulling force in a straight line. It consists essentially of a piston and rod assembly contained within a cylindrical bore which is actuated by the pressure and flow of a hydraulic fluid to produce mechanical force and linear motion.

The proper selection of a hydraulic cylinder requires the consideration of numerous factors influenced by the expected application. Those factors include the amount of force required, cylinder mounting style, stroke length, speed, operating pressure, direction of force, and means of stopping the work load after it is put in motion. Consideration to all these factors is necessary to adequately determine the required cylinder specifications to meet any given application.

Factors to Consider in the Selection of a Hydraulic Cylinder: 

1. Mass

The first and most critical step is to determine the amount of mass you wish to move. Once your mass is known, you must then consider the effect that the mass will have on the force required to move it. For example, a 1-ton load being pushed straight up will require just over 1 ton of force, however, a 1-ton load being pushed across the ground will require only enough force to overcome friction and acceleration. Regardless, the force of the cylinder should always be high enough to allow for margin of error.

2. Geometry

Once you know the nature of the mass being moved you then need to consider the geometry involved in moving it. For a machine such as a hydraulic press, which moves typically up and down, the geometry is simple and requires no further consideration. However, when the centre of the load being moved is not centered on the point of lift force and at perpendicular angles to that point of lift force, the force required by the cylinder changes. If you have a crane, for example, the cylinder pushes on the boom often very far from the load. In most cases the load distance (distance from load to fulcrum) can be up to ten times the lift force (distance from lift force to fulcrum), and sometimes more. So the closer your point of lift is to the fulcrum the more force is required by the cylinder to lift the load.

If you don&#;t know how to perform the calculations specified in this hydraulic selection guide, speak to someone who does. Our dedicated hydraulic engineering team at Berendsen, who assisted in creating this hydraulic selection guide, have the engineering expertise to calculate the required forces for any application.

3. Bore Size

Once you arrive at the force required by your cylinder, the next step is to calculate the bore size required of the cylinder. The force produced by the cylinder is simply the product of the system pressure multiplied by the area of the internal piston surface upon which that pressure acts. This formula is used to calculate the bore size needed to achieve that force.

4. Rod Size

Once a minimum cylinder bore size is determined the next step to the selection of a hydraulic cylinder is to select an appropriate rod size. Most standard off the shelf cylinders usually come with one or two rod options. Selecting the required rod size requires careful consideration of the stroke length required which affects the rod buckling strength. At Berendsen we use programs that calculate whether rod buckling strength for a given rod size and stroke will be suitable for a given load. If you need assistance with this or need a more customised hydraulic selection guide, simply contact us.

In addition to rod buckling, bearing loads is another important consideration in the selection of a hydraulic cylinder. As the stroke length of a cylinder increases, the resultant bearing loads on the piston rod also become greater. To keep these bearing loads from exceeding design limitations stop tubes are usually used. Generally, for applications with strokes greater than mm, stop tubes are required.

When selecting from standard rod options it is recommended that the smaller rod for a given bore only be used for short stroke push loading or reduced pressure applications, and the larger rod offered be used when wanting to obtain maximum reliability and fatigue life of the rod. However, if it is determined that the required rod diameter exceeds that of the largest available within the selected cylinder bore size, it would then be necessary to reconsider design parameters. Alternatively, it may mean that the application warrants the design of a custom made hydraulic cylinder.

5. Cushions

Once the bore, rod and stroke sizes have been determined another consideration is to whether internal cushions at the end of the cylinder stroke are required. The use of cushions is recommended for deceleration of high speed rods to reduce the energy of the impact of the piston assembly against the cylinder end cap. Cushions are optional and can be supplied at either one or both ends of the cylinder as desired. The use of cushions does not affect cylinder envelope or mounting dimensions.

We hope that this hydraulic selection guide has provided you with the information you need. If you still require additional assistance in the selection of hydraulic cylinders, we would be happy to oblige you. At Berendsen, we have a dedicated hydraulic engineering team that can provide assistance in the selection of Hydraulic cylinders and other hydraulic solutions. Whether it be a cylinder from our standard range or a custom engineered cylinder, we have the expertise to select or design a cylinder to suit any application.

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