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At a glance, how could you differentiate a simple from a double acting hydraulic jack ?

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Question added by LABIB KOOLI , Director of the Sectoral Center for Training in Hotel Technologies at Southern Hammamet , Tunisian Vocational Training Agency (ATFP)
Date Posted: 2015/02/03

Honestly speaking, I did not get this question..

Elke Woofter
by Elke Woofter , Project Assistant , American Technical Associates

single-acting cylinder in a reciprocating engine is a cylinder in which the working fluid acts on one side of the piston only. A single-acting cylinder relies on the load, springs, other cylinders, or the momentum of a flywheel, to push the piston back in the other direction. Single-acting cylinders are found in most kinds of reciprocating engine. They are almost universal in internal combustion engines (e.g. petrol and diesel engines) and are also used in many external combustion engines such as Stirling engines and some steam engines. They are also found in pumps and hydraulic rams.

double-acting cylinder is a cylinder in which the working fluid acts alternately on both sides of the piston. In order to connect the piston in a double-acting cylinder to an external mechanism, such as a crank shaft, a hole must be provided in one end of the cylinder for the piston rod and this is fitted with a gland or 'stuffing box' to prevent escape of the working fluid. Double-acting cylinders are common insteam engines but unusual in other engine types. Many hydraulic and pneumatic cylinders use them where it is needed to produce a force in both directions.

Ridha SAIDANI
by Ridha SAIDANI , Maintenance Manager , SOMIPHOS / Technical Direction

Single-acting cylinders

Single-acting cylinders (SAC) use the pressure imparted by compressed air to create a driving force in one direction (usually out), and a spring to return to the "home" position. More often than not, this type of cylinder has limited extension due to the space the compressed spring takes up. Another downside to SACs is that part of the force produced by the cylinder is lost as it tries to push against the spring.

Double-acting cylinders

Double-acting cylinders (DAC) use the force of air to move in both extend and retract strokes. They have two ports to allow air in, one for outstroke and one for instroke. Stroke length for this design is not limited, however, the piston rod is more vulnerable to buckling and bending. Additional calculations should be performed as well.

LABIB KOOLI
by LABIB KOOLI , Director of the Sectoral Center for Training in Hotel Technologies at Southern Hammamet , Tunisian Vocational Training Agency (ATFP)

  A double acting cylinder hydraulic jack has two command orifices 

a simple one has only one command orifice

 

Vinod Jetley
by Vinod Jetley , Assistant General Manager , State Bank of India

The main difference between this block and the Double-Acting Hydraulic Cylinder block is the representation of the hard stop:

  • The Double-Acting Hydraulic Cylinder block utilizes the elastic model of the stop, which is essentially a combination of a spring and a damper, connected in parallel. The stiffness of the spring, which represents contact stiffness of colliding bodies, is very high, resulting in high-frequency, low-magnitude oscillations at the moment the bodies collide. These oscillations can hardly be noticed experimentally, but they are difficult to process by a numerical simulation and generally decrease numerical efficiency.

  • The hard stop in the Double-Acting Hydraulic Cylinder (Simple) block is represented with the inelastic model, which is essentially a viscous damper with the penetration-dependent damping coefficient. This coefficient is referred to as the penetration coefficient. With inelastic model, no oscillation is generated during an impact, resulting in improved numerical robustness and efficiency. But inelastic stop model has a feature that you must consider while selecting the model: colliding bodies continue slowly moving into each other as long as the contact is loaded with the compressing force. In real life, this phenomenon is similar to collision of two bodies separated by a sizable layer of viscous liquid. It takes some time to squeeze the liquid before bodies themselves come into contact.

Thanks for invitation

I have not answer 

Thanks for the invitation, but I do not have any idea to answer this question.

Wolf Klaas Kinsbergen
by Wolf Klaas Kinsbergen , Managing Director, Designer , ingenieursbureau KB International NV

I answer at a glance....I think by the size of the Cilinder

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