Jonic Engineering

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Double Acting Rod Fed Cylinder

A double acting Rod fed cylinder is a development of the tube fed cylinder design.  The oil is fed via two ports in the rod eye and is transferred along a hollow rod to either side of the piston.  If oil enters the full bore port it must leave the annulus port and visa versa.  In this example the cylinder is mounted on spherical bearing to allow the cylinder to self-align.  The force generated by the cylinder is related to the area upon which the pressure acts. 

This means that the force extending the cylinder which is applied to the full bore is greater than the force to retract the cylinder which is applied to the annulus area.  The annulus area is the area of the full bore less the area of the rod.  This difference in areas means that for a given flow the cylinder will retract faster than it will extend. 

The most vulnerable part of a cylinder is the chromed rod which if damaged will cause an external leak.  This design of cylinder can be used to position the delicate chromed rod away from potential harm.  Due to the fact that there are no protrusions or ports on the outer body this can be shielded with an outer sleeve to further protect the chromed rod.

Advantages Disadvantages
Able to extend and retract a load. Requires two feeds.
Oil filled bore – no corrosion issues. Stroke is less than the closed centres.
Valves can be incorporated to control a varying load. More complex and expensive construction
Chrome rod can be shielded or made safe by position Larger rod required to accommodate oil feeds.


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