Nitrox membrane systems are based around a special semi-permeable „filter“ called a membrane. The membrane is fed with very clean, low pressure air. The air is separated between oxygen and nitrogen within the membrane leaving a higher percentage of oxygen (> 28 - 40%) in the gas that exits the sides of the membrane, and a higher percentage of nitrogen (> 90 - 99%) exiting the top of the membrane. The capacity of the membrane is the amount of nitrox produced. This is then compressed in a suitable HP compressor, the quantity of nitrox must be higher than the delivery rate of the HP compressor due to some loss within the HP compressor.

The membrane therefore has a degree of waste (the nitrogen) so that the amount of air entering the membrane is considerably higher than the nitrox exiting the membrane. This air requirement is the most important factor when sizing either the high pressure storage or the low pressure compressor that feeds the membrane and increases drastically with an increase in oxygen percentage of the nitrox.

L&W membranes are available in two sizes S & L. The L membranes can also be mounted in parallel to produce even higher quantities of nitrox if required (> 800 litre/min).

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Technical Data S membrane
Inlet pressure Oxygen
28% 30% 32% 34% 36% 38% 40%
Outlet capacity (litre/min) at +20°C
4 bar 128 131 134 137 140 143 -
5 bar 163 167 170 174 178 181 185
6 bar 199 203 207 212 216 221 225
7 bar 235 240 246 251 256 261 267
8 bar 273 279 285 291 297 303 309
9 bar 311 318 325 332 339 346 353
10 bar 351 358 366 374 382 390 397
11 bar 391 400 408 417 426 435 443
Air inlet requirement (litre/min) at +20°C
4 bar 117 206 242 299 392 557 -
5 bar 225 256 296 357 444 580 998
6 bar 274 311 361 417 526 662 991
7 bar 324 368 426 494 597 745 1066
8 bar 376 426 495 573 692 864 1190
9 bar 429 487 565 654 793 985 1340
10 bar 484 550 627 741 897 1130 1569
11 bar 543 615 715 830 1022 1304 1869

 

Technical Data L membrane
Inlet pressure Oxygen
28% 30% 32% 34% 36% 38% 40%
Outlet capacity (litre/min) at +20°C
4 bar 250 256 262 268 274 280 -
5 bar 318 325 333 341 348 356 364
6 bar 387 396 406 415 425 434 443
7 bar 458 470 481 492 503 514 515
8 bar 532 545 558 571 584 596 609
9 bar 607 622 637 652 666 681 696
10 bar 685 701 718 735 751 768 784
11 bar 764 783 801 820 838 857 875
Air inlet requirement (litre/min) at +20°C
4 bar 345 401 472 585 768 1093 -
5 bar 438 500 579 698 871 1139 1964
6 bar 534 608 706 818 1027 1302 1950
7 bar 633 718 836 969 1172 1465 2101
8 bar 734 833 970 1124 1360 1700 2346
9 bar 838 952 1108 1284 1559 1941 2644
10 bar 945 1076 1249 1455 1765 2227 3097
11 bar 1062 1204 1402 1632 2012 2571 3691

This data is based on a membrane air inlet temperature of +20°C. Temperatures below +20°C increase the selectivity of the membrane and the capacity and the air requirement is reduced, temperatures above +20°C increase the permeability of the membrane and the capacity and the air inlet requirement increases.</p>