This revision treats the piston and rod as one connected moving assembly and limits the worksheet to an ideal two-chamber axial load balance and nominal direct stress over the declared solid rod area.
Piston-Rod Net Load and Nominal Stress
Enter bore, rod-to-bore diameter ratio and both chamber pressures. The worksheet balances the two effective piston-face forces, then divides the net-load magnitude by solid rod area for nominal direct stress.
Equation Used
- The cylinder is single-rod with circular bore and a solid circular rod.
- Each declared chamber pressure is uniform on its effective piston face.
- Positive net load is extension-directed; negative net load is retraction-directed.
- Nominal direct stress uses the magnitude of net axial load divided by rod area.
- Animation travel is prescribed and does not predict speed or dynamics.
- Seal friction, leakage, pressure loss, end conditions, buckling, yielding, fatigue, threads, stress concentration, side load, mounting, cushioning, ratings and safety factors are excluded.
Replaces an unsupported universal buckling ratio rule with a two-chamber ideal load balance and clearly limited nominal direct stress.
The piston and rod form one translating assembly
ISO's hydraulic-cylinder description identifies a movable piston and piston rod operating within a cylindrical bore. Pressure on the cap-side full piston area and pressure on the rod-side annular area create opposing axial forces.
The animation keeps the piston and rod connected and shows both chamber states. Its travel is prescribed only for inspection; it is not a flow or dynamic simulation.
Rod selection requires the actual cylinder and load case
ISO 6020-2 standardizes interchangeability dimensions for a defined 16 MPa compact series, while Parker selection material separately considers tension and compression loading. This worksheet does not select a rod, mounting or cylinder.
Balance both chamber forces before calculating nominal stress
Parker's cylinder guidance defines full piston area, rod area and rod-side net area, and warns that treating a single-rod cylinder as equal areas across one pressure difference is incorrect. The nominal stress here is only average axial force divided by the declared solid rod area.
A declared two-chamber example
A 100 mm bore with a 50% diameter-ratio rod has 19.63 cm² rod area and 58.90 cm² annular area. At 160 bar cap pressure and zero declared rod-side pressure, ideal net extension-directed load is 125.7 kN and nominal direct rod stress is 64.0 MPa.
Nominal direct stress is not rod capacity
Actual selection can be controlled by material properties, compression buckling, effective unsupported length and end conditions, fatigue, threads, stress concentrations, corrosion, seal friction, pressure transients, mounting and side load. None is solved here.
The former page's universal stroke-to-rod thresholds, preferred production range, failure prediction, life, tolerance and brand examples are unsupported and removed.
Piston-rod worksheet questions
Why use two pressures?
The cap and rod chambers act on different effective areas.
Is nominal stress an allowable stress?
No.
Does the worksheet check buckling?
No. It lacks material, effective length, end conditions and imperfection data.
Does animation speed represent cylinder speed?
No. Travel is prescribed only to show the connected assembly.
Piston-rod and cylinder references
- ISO 6020-2:2015: current compact-series single-rod hydraulic-cylinder scope and interchangeability dimensions.
- Parker, Designing With Cylinders: full piston, rod and net areas, opposing chamber forces and the correct single-rod net-force balance.
- Parker Series HMI selection information: theoretical F=P A force and separate piston-rod selection for tension or compression loading.
Building or designing a mechanism like this?
Explore the precision-engineered motion control hardware used by mechanical engineers, makers, and product designers.
