The ISO 3320 series
The metric series of diameters: bores from 25 to 320 mm, rods from 12 to 360 mm. A size off the series points to an inch cylinder (ISO 3321) or a maker’s own size.
Reference tool — not a selection
Hydraulic cylinders, before they go in an RFQ.
Hydraulic cylinder
Bore, rod, pressure.
Enter the diameters in millimetres and the pressure in bar. The drawing and the RFQ line update with every change.
Bore / rod:
All 130 engineering tools
A seal kit is ordered by the bore, the rod and the stroke. Enter the measurements, and the calculator checks them against the metric series of ISO 3320, works out the areas, the area ratio and the forces at the working pressure, the speeds and the oil volume if you like, draws the cylinder in section and writes the RFQ line.
The forces are theoretical, without friction or back pressure. Seals are made for the cylinder, so its maker and model matter more in the request than any calculation.
How it is worked out
Area, pressure, force.
Two areas
On the piston side the oil acts on the whole area, on the rod side on the annulus: the piston area less the rod section. Their ratio says how much weaker and faster the retraction is than the extension.
Force and speed
Force is pressure times area: 1 bar is 0.1 N per square millimetre. Speed is flow divided by area, and the oil volume is area times stroke.
| Bore, mm | Area, cm2 | Push at 100 bar, kN | At 160 bar, kN | At 250 bar, kN |
|---|---|---|---|---|
| 25 | 4.9 | 4.9 | 7.9 | 12.3 |
| 32 | 8 | 8 | 12.9 | 20.1 |
| 40 | 12.6 | 12.6 | 20.1 | 31.4 |
| 50 | 19.6 | 19.6 | 31.4 | 49.1 |
| 63 | 31.2 | 31.2 | 49.9 | 77.9 |
| 80 | 50.3 | 50.3 | 80.4 | 125.7 |
| 100 | 78.5 | 78.5 | 125.7 | 196.3 |
| 125 | 122.7 | 122.7 | 196.3 | 306.8 |
| 160 | 201.1 | 201.1 | 321.7 | 502.7 |
| 200 | 314.2 | 314.2 | 502.7 | 785.4 |
| 250 | 490.9 | 490.9 | 785.4 | 1227.2 |
| 320 | 804.2 | 804.2 | 1286.8 | 2010.6 |
The forces are theoretical: pressure times piston area, without friction losses. The pull is smaller by the area ratio.
Sources
Diameter series: ISO 3320 (its rod table, 110 to 360 mm, and the note on the R 10 and R 20 preferred number series), the ISO table on hydraulics.ezvirtualtools (bores 25 to 320, rods 12 to 220 mm), ISO 6020-2 and the Atos catalogue (bores 25 to 200 mm). Area and area ratio formulas: hydraulics.ezvirtualtools; force, speed and volume follow from the definitions of pressure and flow.
Before you send the request
Questions about hydraulic cylinders in an RFQ
How do I find the bore without opening the cylinder?
The bore is the inside diameter of the tube. Read it from the cylinder plate or the drawing, or measure it at an open end; the outside diameter of the tube alone does not give it, because the wall thickness varies with the pressure rating.
Why is the pull force smaller than the push force?
On the rod side the oil acts only on the annulus, the piston area less the rod section. The area ratio says by how much: at the same pressure the pull is that many times weaker, and at the same flow the retraction that many times faster.
What if the sizes are not in the ISO 3320 series?
Then it is an inch cylinder (ISO 3321) or a maker’s own size. Quote the measured diameters and the cylinder maker and model; the seals are made to the cylinder, not to the nearest series size.
What should the request include?
The bore, the rod and the stroke, the cylinder maker, model and serial number, the working pressure and the fluid, and photographs of the plate and the rod end.
Sizes clear?
Send the line with a photograph of the plate.
A calculation is a cross-check, not a seal selection. Attach photographs of the plate and the rod, and Vessel Core checks them before an offer goes back.
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