Four-rod Hydraulic Cylinder

The pull rod cylinder has a square or rectangular end cap fixed at both ends of the barrel and passes through the hole at the corner of the end cap through the rod. The end cap is fixed on the barrel by a nut on the end thread of each pull rod. The static seal of the barrel/end cover interface prevents leakage. There are many variants of this design, including the use of more than four tie rods on the cylinder or the use of long bolts on the threaded holes on one end cap.
Most of the cylinders used in industrial and heavy duty applications are of pull rod structure, which generally conforms to the American Fluid Power Association (NFPA) standards. These standards establish dimensional uniformity so that cylinders from multiple manufacturers can be interchanged. However, care should be taken when replacing cylinders, because even if it conforms to NFPA size standards, one cylinder may have the proprietary characteristics of its specific manufacturer, while other manufacturers may not.