Working with ISO Metric Cylinders - Part 1

FLUID POWER - Design Data Sheet 74

Sometime in the future, cylinders and other fluid power components will be built to ISO (International Standards Organization) dimensions in which metric measurements are used. Conversion to international standards has been slow in the United States, and at the time this sheet was prepared the availability of metric dimension cylinders was quite limited, but complete conversion will come in due time.

Cylinder force charts in this sheet cover standardized bore and rod combinations from 25mm through 200mm bore and with standard and maximum size piston rods. Intermediate size piston rods will no doubt be offered by most manufacturers. ISO standard sizes also include bore sizes of 8, 10, 12, 16, 20, 250, 320, and 400mm.

Calculations of cylinder force and velocity are not quite as straightforward as in the U. S. system because of extra conversions between units which become necessary. The ISO units which will be used in cylinder calculations are these:

FORCE. Force values are in Newtons (N). One Newton is equal to about 1/4 pound (0.2248 lb. to be exact), or 1 pound is equal to about 4½ N (4.448 N to be exact). This unit should serve for most cylinder calculations except where very large forces are involved in which the kilo Newton (kN) equal to 1,000 N may be used.

PISTON AREA. Piston bore is cataloged in units of millimeters (mm) as shown in the charts. For area, the mm² is too small for convenient calculations, so the unit for piston surface area will be the square centimeter (cm²). To calculate piston area, change bore diameter to em by dividing by 10. Then, find cm² piston area with the formula: A = πr² in the usual manner.

PRESSURE. Fluid pressure will usually be expressed in kilo Pascals (kPa) because the Pascal, which is defined as one Newton of force per square meter, is such a small unit that it is hard to work with in making calculations. One kPa = 1,000 Pa.

The bar is a more convenient unit for fluid pressure and will be allowed, at least for a limited time. The bar is related to the Pascal. One bar = 100,000 Pascals or 100 kPa. It is also equal to 14.5 PSI which is very close to one atmosphere. Pressure values in these charts are given in three pressure units, bars, kPa, and PSI, to help a person get a “feel” for the way metric pressure units compare with PSI units he has been using.

PUMP FLOW. Oil flow from a hydraulic pump is expressed in liters per minute (1/min). A liter is defined as one cubic decimeter (dm³), and is roughly ¼ gallon (0.2642 gallon to be exact). Or, 1 gal. = 3.785 liters. On very large flows, units of liters per second (lis) can be used.

FORCE CALCULATION. Cylinder force is calculated by multiplying piston surface area times fluid pressure:

F = A × P ÷ 70, in which:

F = force, in Newtons (N).
A = piston area in square centimeters (cm²).
P = differential pressure across ports in kPa.
10 is a necessary conversion between metric units.

When working with pressure in bars, the formula becomes:

F = A × P × 10, in which:

P is differential pressure, in bars.

METRIC HYDRAULIC CYLINDERS - FORCE CHART - 25 TO 175 BARS PRESSURE

 Bars 25 50 75 100 125 150 175 Kilo Pascals 2,500 5,000 7,500 10,000 12,500 15,000 17,500 PSI 363 725 1,088 1,450 1,813 2,175 2,538 Bore mm. Bore cm. Area sq. cm. Theoretical Cylinder Force in Newtons 25 2.5 4.91 1,227 2,454 3,680 4,907 6,138 7,361 8,587 32 3.2 8.04 2,011 4,021 6,032 8,042 10,053 10,053 12,063 40 4.0 12.57 3,142 6,283 9,425 12,566 15,708 18,849 21,991 50 5.0 19.63 4,909 9,817 14,726 19,634 24,543 29,451 34,360 63 6.3 31.17 7,793 15,585 23,378 31,170 38,963 46,755 54,548 80 8.0 50.27 12,566 25,133 37,699 50,265 62,831 75,398 87,964 100 10.0 78.54 19,935 39,270 58,904 78,539 98,174 117,809 137,443 125 12.5 122.72 30,679 61,358 92,037 122,716 153,395 184,074 214,753 160 16.0 201.06 50,265 100,531 150,796 201,061 251,326 301,592 351,857 200 20.0 314.16 78,540 157,080 235,619 314,159 392,699 471,239 549,778

METRIC HYDRAULIC CYLINDERS - FORCE CHART - 200 TO 350 BARS PRESSURE

 Bars 200 225 250 275 300 325 350 Kilo Pascals 20,000 22,500 25,000 27,500 30,000 32,500 35,000 PSI 2,900 3,263 3,625 3,988 4,350 4,713 5,075 Bore mm. Bore cm. Area sq. cm. Theoretical Cylinder Force in Newtons 25 2.5 4.91 9,814 11,041 12,268 13,494 14,721 15,948 17,175 32 3.2 8.04 16,084 18,095 20,105 22,116 24,126 26,137 28,147 40 4.0 12.57 25,132 28,274 31,415 34,557 37,698 40,840 43,981 50 5.0 19.63 39,268 44,177 49,805 53,994 58,902 63,811 68,719 63 6.3 31.17 62,340 70,133 77,925 85,718 93,510 101,303 109,095 80 8.0 50.27 100,530 113,096 125,663 138,229 150,795 163,361 175,928 100 10.0 78.54 157,078 176,713 196,348 215,982 235,617 255,252 274,887 125 12.5 122.72 245,432 276,111 306,790 337,469 368,148 398,827 429,506 160 16.0 201.06 402,122 452,387 502,653 552,918 603,183 653,448 703,714 200 20.0 314.16 628,318 706,858 785,398 863,937 942,477 1,021,017 1,099,557

METRIC AIR CYLINDERS - FORCE CHART - 3 TO 6 BARS PRESSURE

 Bars 3 3½ 4 4½ 5 5½ 6 Kilo Pascals 300 350 400 450 500 550 600 PSI 43.5 50.8 58.0 65.3 72.5 79.8 87.0 Bore mm. Bore cm. Area sq. cm. Theoretical Cylinder Force in Newtons 25 2.5 4.91 147 172 196 221 245 270 294 32 3.2 8.04 241 281 322 362 402 442 483 40 4.0 12.57 377 440 503 565 628 691 754 50 5.0 19.63 589 687 785 884 982 1,080 1,178 63 6.3 31.17 935 1,091 1,247 1,403 1,559 1,714 1,870 80 8.0 50.27 1,508 1,759 2,011 2,262 2,513 2,765 3,016 100 10.0 78.54 2,356 2,749 3,142 3,534 3,927 4,320 4,712 125 12.5 122.72 3,681 4,295 4,909 5,522 6,136 6,749 7,363 160 16.0 201.06 6,032 7,037 8,042 9,048 10,053 11,058 12,064 200 20.0 314.16 9,225 10,996 12,566 14,137 15,708 17,279 18,850

METRIC AIR CYLINDERS - FORCE CHART - 6½ TO 11 BARS PRESSURE

 Bars 6½ 7 7½ 8 9 10 11 Kilo Pascals 650 700 750 800 900 1,000 1,100 PSI 94.3 102 109 116 131 145 160 Bore mm. Bore cm. Area sq. cm. Theoretical Cylinder Force in Newtons 25 2.5 4.91 319 343 368 393 442 491 540 32 3.2 8.04 523 563 603 643 724 804 885 40 4.0 12.57 817 880 942 1,005 1,131 1,257 1,382 50 5.0 19.63 1,276 1,374 1,473 1,571 1,767 1,963 2,160 63 6.3 31.17 2,026 2,182 2,338 2,494 2,805 3,117 3,429 80 8.0 50.27 3,267 3,519 3,770 4,021 4,524 5,027 5,529 100 10.0 78.54 5,105 5,498 5,890 6,283 7,069 7,854 8,639 125 12.5 122.72 7,977 8,590 9,204 9,817 11,044 12,272 13,499 160 16.0 201.06 13,069 14,072 15,080 16,085 18,095 20,106 22,117 200 20.0 314.16 20,420 21,991 23,562 25,133 28,274 31,416 34,557

CROSSOVER - METRIC TO INCH BORE SIZES

 Metricmm. ExactInches App.Inches Metricmm. ExactInches App.Inches 25 0.984 1 80 3.150 3¼ 32 1.260 1¼ 100 3.937 4 40 1.575 1½ 125 4.921 5 50 1.969 2 160 6.300 6½ 63 2.362 2½ 200 7.874 8

© 1990 by Womack Machine Supply Co. This company assumes no liability for errors in data nor in safe and/or satisfactory operation of equipment designed from this information.