Pipes and PSI: Calculating Flow at Different Pressures

The pressure in a pipe depends on static, working outlet pressure, distance and flow rate.

For what you want to know you need to plot a system curve.

Take a flow calculate friction loss per unit length. multiply by length and add the lot.

if this is repeated for different flows the curve can be plotted.

Your answer can be obtained from the system curve.

Is this a problem from a class or the real world?

I think you need to give us more details of your pipe situation.

Do you know the flow at 95psi?

If there is a pump in the system, then you can calculate the head loss in the pipe, the fittings (elbows, tees, etc), the valves, strainers, filters, etc and add any elevation head if it is not closed loop. THEN plot the calculated pressure on the pump curve and whereever they intersect you should be able to read the flow rate.

To get the flow at a different pressure (I'm assuming this is hea loss), realize that the pressure loss is proportional to velocity squared. Double the velocity in the pipe and the head will increase by a factor of four. Halve the velocity and the new head loss will be one fourth of the original.

Check out the Cameron Hydraulic Data book. It has the loss for all the pipe fittings. Lots of fluid mechanics books will have that data also.

I have 1 ft. of 1/2in. sch.40 pvc feeding a 6 way distributor the 6 ports feed 18in. 0f 1/4in micro tubing with a fogger head that has an operating pressure of 40 to 80 psi. What I need to know is how much pump i need to get the pressure range required.

A 50 gpm pump at 45 psi will deliver 40 psi at the sprayers.

The same pump at 85 psi will deliver 80 psi at sprayers.

There's a whole bunch of factors you gotta take into consideration: pipe type, roughness, rust, water slime, Reynolds number, velocity, etc. If I had much to do, I'd join efunda for a month ($6) and use their nifty calculator. If I was broke as I usually am, I'd get out my trusty old pipe charts (in my beatup 3rd edition of Mark's Handbook) and look it up there.

what is water slime

what is efunda how can i download it

is it same as spirex sarco calculator

Slime

This commenter was suggesting that the actual pipe friction may be less due to some biological growth in the pipeline and that you may want to take this into account in your analysis.

efunda

One of many program solutions to the charts and graphs given in any (i.e. Cameron) pipe handbook.

spirex sarco

similar answer to "efunda" question above. Yet another program solution to picking numbers off a chart.

Get either the charts or the programs and get busy. More information will be required irregardless of which tool (paper chart or electronic solution) you use. See other posts for what (input) is required.

You can try the following link.

http://www.spiraxsarco.com/us/resources/calculators/pipes.asp

Yes Dweezle,

It is very interesting site which includes a lot of Calculators with a great help for whom interested in fluid mechanics of water mixing and steam.

95 lbs through what size pipe? valves open or closed?

come on now the flow could be anyn thing - zero or a million gallons a minute!

Pressure and flow are interdependent but many other known factors are required to make a determination of your request.

Firstly what kind of instrument you are using to measure the flow? Let me suggest you this, You can use a Verabar flow meter or any Dp flow meter in which you will take two tappings. From this tappings you will get the Dp which is later calibrated in terms of flow. From the same tappings you can also calculate the Presure in the line using a Pressure Transmitter. So when ever you get the flow in the line you can also read the pressure at that point too. Making it simple, use a Bourdon Tube Pressure Gauge or transmitter immediately before the flow meter (3XD distance before the flowmeter is advisable; where D is the diameter of the pipe)

Knowing the pressure of any liquid inside any pipe is not a sufficient data to calculate the flow rate, since there are a lot of flow rates can be established at the same pressure. But knowing the ΔP inside the pipe by throttling (using orifice flange with orifice plate) can be connected to a flow transmitter FT and flow indicator FI.

So, no way to find the flow rate for certain case with a pressure 95 psi nor 65 psi, unless you have a full system hydraulic data.

I can see a lot of bullshit comments, it's simply:

Q=¼πD² √(2P/ρ)

Q = flowrate

π = 3.14

D = inside diameter

P = pressure difference

ρ = density of fluid

N.B. units to be consistent

What units for Q? Is that in gpm?

hey guys, your are all right: flow calculations can be quite difficult. But I think we should go for a most simple approach first ...

The most simple anwer is: one flow rate (for a certain fluid pressure) must be measured - use a bucket or a drum and fill in the flow for 60 or 120 seconds. Then the flow rate is: Q = Volume/(number of minutes). If you can't do this job you really are faced with all the things asked and mentioned by the other contributors.

Assuming the flow resistances would not change their character (laminar, turbulent) a sufficient approximation about effects on flow due to changing fluid pressures can be made with:

Q2 = Q1 √(p2 / p1) ; with pressures as gauge-pressures

For water this kind of recalculation can be made in case the pressure deviations are moderate, for instance +/-30%. Let's say, such approximation gives a sufficient idea what results can be expected.

If you're looking to calculate the flow with equations on a straight run of pipe, you need to use the Bernoulli equation. For a branched section of pipe, you will need to use an iterative process such as the Hardy-Cross method.

For finding flow without calculations, I've used an ultrasonic flow meter before. You just need to have a pressure gauge to make sure the flow you measure is at the pressure you want.

Without reading more into the question I would suggest the flow charts available at www.elkhartbrass.com. I tried to cut and paste the chart, but I just can't cut it. I hope this helps.

i search for elkartbrass but it has several links where will i get exactly the flow chart what is this actually elkartbrass, as it has several links where i can get good engineering information

Look for nozzle flow rates.

please attach the link for me i m tired after too much search.

the page is....

http://www.elkhartbrass.com/files/aa/downloads/performance/%20Smooth%20Bore%20Discharge.pdf

I hope this helps.

Nozzle Diameter in Inches

1/4" 3/8" 7/16" 1/2" 5/8" 3/4" 7/8" 15/16" 1.0" 11/8" 11/4" 13/8" 11/2" 15/8" 13/4" 17/8" 2.0" 21/4" 21/2" 3.0"

Gallons Per Minute

20 8 18 25 33 51 75 101 115 132 167 206 250 298 350 407 468 532 674 832 1200

22 8 19 26 34 54 79 105 122 139 175 216 263 313 367 427 490 557 707 872 1255

24 8 20 27 36 56 82 110 127 145 183 226 275 327 384 446 512 582 739 910 1311

26 9 21 29 37 59 85 115 133 151 191 235 286 340 400 464 533 606 769 949 1366

28 9 21 30 39 61 89 119 138 157 198 244 297 353 415 481 554 629 799 985 1418

30 10 22 31 40 63 92 123 142 162 205 253 307 365 429 498 572 651 826 1017 1470

32 10 23 32 41 65 95 127 147 167 212 261 317 377 443 514 591 673 854 1050 1515

34 11 23 33 43 67 98 131 152 172 218 269 327 389 457 530 610 693 880 1082 1561

36 11 24 34 44 69 100 135 156 177 224 277 336 400 470 546 627 713 905 1114 1610

38 11 25 35 45 71 103 138 160 182 231 285 345 411 483 561 645 733 930 1144 1650

40 11 26 35 46 73 106 142 165 187 237 292 354 422 496 575 661 752 954 1174 1692

42 11 26 36 47 74 109 146 169 192 243 299 363 432 508 589 678 770 978 1203 1737

44 12 27 37 49 76 111 149 173 196 248 306 372 442 520 603 694 788 1000 1231 1776

46 12 28 38 50 78 114 152 176 200 254 313 380 452 531 617 710 806 1021 1259 1816

48 12 28 39 51 80 116 156 180 205 259 320 388 462 543 630 725 824 1043 1286 1854

50 13 29 40 52 81 118 159 184 209 265 326 396 472 554 643 740 841 1065 1313 1895

52 13 29 40 53 82 121 162 188 213 270 333 404 481 565 656 754 857 1087 1339 1930

54 13 30 41 54 84 123 165 191 217 275 339 412 490 576 668 769 873 1108 1364 1968

56 13 30 42 55 86 125 168 195 221 280 345 419 499 586 680 782 889 1129 1389 2000

58 13 31 43 56 87 128 171 198 225 285 351 426 508 596 692 796 905 1149 1417 2020

60 14 31 43 57 89 130 174 201 229 290 357 434 517 607 704 810 920 1167 1438 2075

62 14 32 44 58 90 132 177 205 233 295 363 441 525 617 716 823 936 1187 1463 2108

64 14 32 45 59 92 134 180 208 237 299 369 448 533 627 727 836 951 1206 1490 2140

66 14 33 46 60 93 136 182 211 240 304 375 455 542 636 738 850 965 1224 1510 2175

68 14 33 46 60 95 138 185 214 244 308 381 462 550 646 750 862 980 1242 1532 2205

70 15 34 47 61 96 140 188 218 247 313 386 469 558 655 761 875 994 1260 1558 2240

72 15 34 48 62 97 142 191 221 251 318 391 475 566 665 771 887 1008 1278 1579 2275

74 15 35 48 63 99 144 193 224 254 322 397 482 574 674 782 900 1023 1296 1600 2300

76 15 35 49 64 100 146 196 227 258 326 402 488 582 683 792 911 1036 1313 1620 2340

78 15 36 50 65 101 148 198 230 261 330 407 494 589 692 803 924 1050 1330 1640 2370

80 16 36 50 66 103 150 201 233 265 335 413 500 596 700 813 935 1063 1347 1665 2400

82 16 37 51 66 104 152 204 235 268 339 418 507 604 709 823 946 1076 1364 1685 2425

84 16 37 51 67 105 154 206 238 271 343 423 513 611 718 833 959 1089 1380 1707 2460

86 16 37 52 68 107 155 208 241 274 347 428 519 618 726 843 970 1102 1396 1723 2485

88 16 38 53 69 108 157 211 244 277 351 433 525 626 735 853 981 1115 1412 1745 2515

90 17 39 53 70 109 159 213 248 280 355 438 531 633 743 862 992 1128 1429 1762 2540

92 17 39 54 70 110 161 215 249 283 359 443 537 640 751 872 1002 1140 1445 1785 2565

94 17 39 54 71 111 162 218 252 286 363 447 543 647 759 881 1012 1152 1460 1802 2600

96 17 40 55 72 113 164 220 255 289 367 452 549 654 767 890 1022 1164 1476 1822 2625

98 17 40 55 73 114 166 223 257 292 370 456 554 660 775 900 1032 1176 1491 1840 2650

100 18 41 56 73 115 168 225 260 295 374 461 560 667 783 909 1043 1189 1506 1860 2680

105 18 42 57 75 118 172 230 266 303 383 473 574 683 803 932 1070 1218 1542 1908 2745

110 19 43 59 77 121 176 236 273 310 392 484 588 699 822 954 1095 1247 1579 1950 2810

115 19 43 60 79 123 180 241 279 317 401 495 600 715 840 975 1120 1275 1615 1995 2875

120 19 44 61 80 126 183 246 285 324 410 505 613 730 858 996 1144 1303 1649 2020 2940

125 20 45 63 82 129 187 251 291 331 418 516 626 745 876 1016 1168 1329 1683 2080 3000

130 20 46 64 84 131 191 256 295 337 427 526 638 760 893 1036 1191 1356 1717 2120 3055

135 21 47 65 85 134 195 262 302 343 435 536 650 775 910 1056 1213 1382 1750 2160 3110

140 21 48 66 87 136 198 266 308 350 443 546 662 789 927 1076 1235 1407 1780 2200 3170

145 21 49 68 88 139 202 271 313 356 450 556 674 803 944 1095 1257 1432 1812 2240 3225

150 22 50 69 90 141 205 275 318 362 458 565 686 817 960 1114 1279 1456 1843 2260 3280

175 24 55 74 97 152 218 298 344 390 494 610 740 883 1030 1200 1380 1572 1985 2460 3540

200 26 59 79 104 162 234 318 368 418 527 653 790 944 1103 1283 1472 1680 2123 2635 3785

Nozzle

Pressure

in psi*

GPM = 29.71 d2 √NP

GPM = Gallons per minute

29.71 = Constant

d = Diameter of nozzle orifice (inches)

NP = Nozzle pressure (psi) measured by pitot tube and gauge

DISCHARGE OF SMOOTH BORE NOZZLES/TIPS

* Nozzle pressure measured by pitot tube and gauge.

FORMULA FOR DISCHARGE OF SMOOTH BORE NOZZLES:

ELKHART BRASS MFG. CO., INC. • 800.346.0250 • 1.574.295.8330 • FAX: 574.293.9914 • www.elkhartbrass.com

SMOOTH BORE

DISCHARGE

hai i have doubt on flow the medium pressure steam economic velocity 25m/S (8BAR). depend on this i calculte the pipe diameter , if velocity is raised to 30m/s what is the pressue. exact question in 8 bar steam pressure how much velocity head how we calculate.