COMPRESSED AIR PIPE SIZING CALCULATION So, you want to know the correct pipe size for your compressed air installation? It easy, I'll explain how. I still see too many places where the pipe size of the compressed air system is too small. It's either because the factory or workshop has grown over time, and the old system became too small !uite understandable", or they #ust installed a too small pipe to begin with$ %hat's the problem with a too small compressed air pipe? &ressure drop$ If too much air needs to pass a too small pipe, it will have trouble passing through this pipe. he result is a pressure drop between the beginning of the pipe and the end of the pipe. (ow, what's the problem with pressure drop you ask? )oney$ If the pressure drop becomes too high, you will need to set your compressor on a higher setpoint. he higher the setpoint of your compressor, the the more energy and money" it will use. herefore, the pressure drop should be maximum *,+$ his means that the pressure at the pointof use should be maximum *.+ bar lower than the pressure at the compressor outlet. -or example ./ bar at the pointof use and 0 bar at the compressor.
What infuences pressure drp! In short, every obstruction creates a pressure drop. he pipes themselves of course. 1ut also bends in the pipe, couplings, flexible hoses, h oses, !uickconnect coupling, they all create a pressure drops. 2nd, the longer the pipe, the bigger the pressure drop will be. he amount of air passing through the pipe is also a factor. he more air needs to pass through a pipe at once, the bigger the pressure drop. his also means, that when no air is used at all at night, in the weekends", there is no pressure drop. hat's why you always need to measure the pressure drop at full air consumption all machines3air tools running, worst case scenario". In short, the information we need to calculate pressure drop are4 •
5iameter of pipe
•
6ength of pipe
•
(umber of bends, couplings, etc
•
Air f"
2ir flow through pipe
o start, you need to know the air flow through your system. he easiest way to find out the maximum" air flow, is too look at the specs of your compressor look i n the manual or search online". here will always be one line that tells you the maximum output of the machine in liters3second, m7 per minute or hour, or cubic feet per minute cfpm". his is the maximum amount of air the compressor is able to pump out, at the rated pressure. 1ut be careful, there is one important thing to look out for89:
#$s %s& N#$s 'r c(p) %s Sc(p)*& he air flow that is stated in the compressor specs, is most of the time (l3s or S cfpm", which means ;(ormal liters per second; or standard cubic feet per minute". It means that the values are given at standard or reference conditions, which are + bar, <* degrees =elsius and *> relative humidity. ften, the flow is stated as -25, which means ;-ree 2ir 5elivery;, which means the same thing4 calculated back to reference conditions more or less atmospheric air, like you and me breathe". So in fact, the -25 (ormal liters per second, or Scfpm", is actually the amount of air that is sucked in by the compressor per minute.@ It is compressed, and then transported through the piping system. So at 0 bar pressure, the liters per minute without the 'normal' " is about 0 times smaller compared to the normal liters per second. his difference is so often overlookedA most people don't know about it and use the wrong terminology even in compressor specifications sometimes$".
C)pressed air pipe si+e ta,#e (ow instead of giving you complicated formulas to calculate the pressure drop, here is a simple table that will answer all your pipe sizing !uestions. 6ook up your compressors maximum flow rate in the left column. (ow, measure or calculate the total length of your compressed air pipes and a nd look it up in the top row. (ow you can read the correct pipe size in mm diameter" in the table. his table is for 0 bars and maximum *.7 bar pressure drop. he value given is for a straight pipe without any bends, b ends, couplings or other restrictions. Bow to calculate the influence of those can be found in the next paragraph.
Table Tabl e 1: Compressed air pipe sizing table (in millimeters).
N m3/h S cfpm
50m
100m
150m
300m
500m
750m
1000m
2000m
164ft
328ft
492ft
984ft
1640ft
2460ft
3280ft
6561ft
15
15
15
20
20
25
25
25
10
6
30
18
15 15
15
15
25
25
25
25
40
50
29
15 15
25
25
25
40
40
40
40
70
41
25 25
25
25
40
40
40
40
40
100
59
25 25
25
40
40
40
40
40
63
150
88
25 25
40
40
40
40
40
40
63
250
147
40
40
40
40
63
63
63
63
350
206
40
40
40
63
63
63
63
80
500
294
40
40
63
63
63
63
63
80
750
441
40
63
63
63
63
80
80
100
1000
589
63
63
63
63
63
80
80
100
1250
736
63
63
63
63
63
100
100
100
1500
883
63
63
63
80
80
100
100
125
1750
1030
63
63
80
80
80
100
100
125
2000
1177
63
80
80
80
100
100
100
125
2500
1471
63
80
80
80
100
125
125
125
3000
1766
80
80
76
100
100
125
125
150
3500
2060
80
80
100
100
125
125
125
150
4000
2354
80
100
100
100
125
125
125
150
4500
2649
80
100
100
125
125
125
150
150
5000
2943
80
100
100
125
125
150
150
150
Infuence ( ,ends- cup#in.s and ther stu/ t pressure drp 2s said before, bends, couplings and other kinds of restrictions restrictions will increase the pressure drop. drop.
2 pipe with one bend in it will have a greater pressure drop compared to a pipe with no bend. 2 pipe with a bend and a coupling will have an even greater pressure drop. (ow, I could give you all sorts of difficult formulas, but I know an easier way. 1elow is a table to lookup what is called the ' equivalent pipe length' for a generated pressure drop. It is simply a way to express the pressure drop for a certain bend or coupling will create, but not in bars or psi" but in 'virtual' added pipe length. Simply add extra 'virtual' meters of pipe to your pressure drop calculation table + above" a bove" for every bend or valve in your system.
E0ui%a#ent pipe #en.th ta,#e 1elow table <" is the e!uivalent e!uiva lent pipe length table. he value depends on the pipe diameter. 2 valve in a small diameter pipe will have a different influence compared to a valve in a big diameter pipe. o find out the e!uivalent pipe length for the valve or bend in your system, simply look under the pipe diameter of your compressed air system to find the e!uivalent pipe length of the valve or bend. Table Tabl e 2. Equivalent pipe length table (values in meters).
25 mm
40 mm
50 mm
80 mm
100 mm 125 mm 150 mm
Bend 90 degrees R 0.3 =d
0.5
0. 6
1.0
1.5
2.0
2 .5
Bend 90 degrees R 0.15 = 2d
0.25
0. 3
0.5
0.8
1.0
1 .5
Knee-end !90 degrees"
1.5
2.5
3. 5
5
7
10
15
#-p$ece
2
3
4
7
10
15
20
%hec& '()'e
8
10
15
25
30
50
60
*$(phr(gm '()'e
1.2
2.0
3. 0
4.5
6
8
10
+(te '()'e
0.3
0.5
0. 7
1.0
1.5
2.0
2 .5
-or example a kneebend in a
E1a)p#e ca#cu#atin ( re0uired pipe dia)eter& Bere's an example calculation using the compressed air pipe sizing table table +" and the e!uivalent pipe length table table <". 6et's say we have a rotary screw compressor of 7* k% that can supply
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