Hydraulics & Fluid Power Reference Library · Technical Reference

Hydraulic Cylinders (Tie-Rod, Welded, Telescopic)

Hydraulic cylinders turn pressure into straight-line force. Tie-rod, welded and telescopic cylinders are built differently, and the mounting style must suit how the load pushes and pulls on the cylinder.

Ref HY-0027ISO 6020ISO 6022NFPA T3.6.7

Draft, open for review. Check every value against the governing standard and the manufacturer’s data before use.

What it is

A cylinder has a barrel, a piston on a rod, a head (rod end) and a cap (blind end). Oil pushes the piston to extend or retract the rod. The three common constructions are:

Tie-rod: square heads and caps held to the barrel by long threaded rods. Common in factory automation. Built to NFPA and ISO interchangeable dimensions.
Welded body: the cap is welded to the barrel and the head is threaded or retained. Compact and common on mobile equipment.
Telescopic: several nested stages that extend one after another for long stroke from a short retracted length. Used on dump bodies and lifts. Many are single-acting.

How to identify

Tie-rod cylinders show four or more exposed rods running the length of the barrel. Welded cylinders have a smooth round barrel with a welded end. Telescopic cylinders show several sleeves of different diameters when extended. Measure bore, rod diameter, stroke, retracted length and mounting, and read any tag before ordering a replacement or seal kit.

Mounting styles

Mounting group	Examples	Load path	Best for
Fixed, centerline	Head or cap flange, extended tie rods	In line with the rod	Straight push or pull, no pivoting
Fixed, non-centerline	Side lugs, side tapped, foot mounts	Offset from the rod	Machine bases where load is guided
Pivot	Cap clevis, cap eye, spherical bearing	In line, can swing in one plane	Loads that move in an arc
Trunnion	Head, cap or intermediate trunnion	In line, pivots on pins	Arc motion with mounting near mid-length

NFPA tie-rod mounting styles use letter codes (MX for extended tie rods, MF for flanges, MP for pivots, MS for side mounts, MT for trunnions) with a number for the position. Check the code and dimensions against NFPA T3.6.7 or the maker's catalog.

Key points

Pivot mounts take misalignment. Fixed mounts need the load to be well guided, or the rod and seals will wear.
Long strokes in push need stop tubes or a larger rod to resist buckling. Use the maker's rod sizing charts.
ISO 6020 and ISO 6022 define interchangeable dimensions for different series. Same bore does not mean same mounting.
Pressure and force capacity come from the maker's rating. Do not assume a rating from the bore size.
Cushions slow the piston at the end of stroke and are set with an adjusting screw on many tie-rod cylinders.

Common mistakes

Replacing a cylinder by bore and stroke only and missing the mount type or pin size.
Side loading a fixed-mount cylinder.
Treating a single-acting telescopic as double-acting.
Removing a cylinder with a raised load or stored pressure.

Governing standards: NFPA T3.6.7 (square head tie-rod cylinder dimensions); ISO 6020 and ISO 6022 (mounting dimensions); ISO 6099 (mounting identification).

Reference only. Verify against the current governing code or standard, the manufacturer's data and the project documents before use. Apps for Distributors disclaims liability arising from reliance on this reference.

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