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RHM Home > Tech Tips > Line Sizing and Fluid Velocity
Line Sizing and Fluid Velocity PDF Print E-mail

Line size selection
Selecting the proper line size for a hydraulic system is critical to get maximum performance and life from your hydraulic components. The four basic line types in a hydraulic system are:  Pump suction, Return (Low pressure <100 PSI), Medium pressure (500 to 2000 PSI), and High Pressure (2100 to 5000 PSI). Under-sizing fluid lines will result in high pressure loss and system overheating. Over sizing lines increases the cost of the system. Lines should be sized as follows:

  • Suction: 2-4 feet/sec.
  • Return: 10-15 feet/sec.
  • Medium Pressure: 15-20 feet/sec.
  • High Pressure:  20-25 feet/sec.

On extremely long lines the pressure drop through the pressure and return lines must be accounted for to insure sufficient pressure is available at the actuator.

(See pressure drop charts included with this document).

Fluid Velocity
Velocity through a line can be calculated with the formula:

Velocity = GPM x 0.3208
                       Area
Velocity = Feet Per Second (fps)
GPM = Gallon per minute fluid flow
A = Square inch inside area of conductor


The Following velocity charts are a quick way to check velocity through a line.  Included in the charts is the I.D. of the line. If the particular tube, pipe or hose you are using is not listed, reference a line with a similar I.D. for approximate velocity.

Approximate Velocity in GPM – Schedule 40 Pipe           

Size I.D. 2fps 4fps 10fps 15fps 20fps
3/8" 0.493" 1.2 2.3 5.9 8.9 11.9
1/2" 0.622" 1.9 3.8 9.5 14.2 18.9
3/4" 0.824" 3.3 6.6 16.6 24.9 33.2
1" 1.049" 5.4 10.7 26.9 40.4 53.9
1-1/4" 1.38" 9.3 18.6 46.6 69.9 93.2
1-1/2" 1.610" 12.7 25.3 63.5 95.2 126.9
2" 2.067" 20.9 41.8 104.6 156.9 209.2
2-1/2" 2.469" 29.8 59.7 149.2 223.8 298.5
3" 3.068" 46.1 92.1 230.4 345.6 460.8
4" 4.026" 79.4 158.7 396.8 595.2 793.6
6" 6.065" 180.1 360.2 900.5 1350.7 1801



Approximate Velocity in GPM – Schedule 80 Pipe    

Size I.D. 2fps 4fps 10fps 15fps 20fps 25fps
3/8" 0.423" 0.9 1.75 4.4 6.6 8.8 11
1/2" 0.546" 1.5 2.9 7.3 10.9 14.6 18.2
3/4" 0.742" 2.7 5.4 13.5 20.2 27 33.7
1" 0.957" 4.5 8.9 22.4 33.6 44.8 56
1-1/4" 1.278" 8 16 40 60 80 100
1-1/2" 1.5" 11 22 55.1 82.6 110.2 137.7
2" 1.939" 18.4 36.8 92 138.1 184.1 230.1
2-1/2" 2.323" 26.4 52.8 132.1 198.2 264.2 330.3
3" 2.9" 41.2 82.3 205.9 308.8 411.8 514.7
4" 3.826" 71.7 143.4 358.3 537.5 716.7 895.9
6" 5.761" 162.5 325.1 812.5 1218.7 1624.9 2031.2


Approximate Velocity in Tubing

Size I.D. 2fps 4fps 10fps 15fps 20fps 25fps
3/8" x .049 wall 0.277" 0.38 0.75 1.88 2.81 3.75 4.69
1/2" x .064 wall 0.37" 0.67 1.34 3.35 5.03 6.7 8.37
3/4" x .109 wall 0.532" 1.39 2.77 6.93 10.4 13.9 17.31
1" x .120 wall 0.76" 2.83 5.65 14.1 21.2 28.3 35.33
1-1/4" x .120 wall 1.01" 5 10 25 37.4 50 62.4
1-1/2" x .120 wall 1.26" 7.77 15.5 38.8 58.3 77.7 97.12



Pressure Drop
Pressure drop through the conductor must be accounted for in long runs of pipe, hose or tubing. This will insure you have sufficient pressure available at your actuator to do work and sufficient horsepower available at the pump. You can use the following charts to estimate total pressure drop through a conductor based on fluid velocity. Included in the charts is the I.D. of the conductor, so if the particular tube or pipe you are using is not listed you can reference a conductor with a similar I.D. for approximate pressure drop.

Fluid viscosity plays a very large part in calculating pressure drop through the system. The charts below are based on ISO grade 46 Hydraulic oil with a viscosity of approximately 225 S.S.U. at 100°F and .88 specific gravity. Actual pressure drop will increase as viscosity increases.



Approximate Pressure Drop (PSI) per 1 Foot of line length – Schedule 40 Pipe                

Size I.D. 2fps 4fps 10fps 15fps 20fps 25fps
3/8" .493" 0.18 0.36 0.91 1.36 2.98 4.4
1/2" .622" 0.11 0.23 0.57 1.35 2.23 3.29
3/4" .824" 0.06 0.13 0.32 0.95 1.57 2.31
1" 1.049" 0.04 0.08 0.34 0.7 1.16 1.71
1-1/4" 1.38" 0.02 0.05 0.24 0.5 0.82 1.21
1-1/2" 1.610" 0.02 0.04 0.2 0.41 0.68 1
2" 2.067" 0.02 0.04 0.15 0.3 0.5 0.73
2-1/2" 2.469" 0.01 0.03 0.12 0.24 0.4 0.59
3" 3.068" 0.01 0.02 0.09 0.18 0.3 0.45
4" 4.026" 0.01 0.02 0.06 0.13 0.22 0.32
6" 6.065" 0.004 0.01 0.04 0.07 0.12 0.18


Approximate Pressure Drop (PSI) per 1 Foot of line length – Schedule 80 Pipe

Size I.D. 2fps 4fps 10fps 15fps 20fps 25fps
3/8" 0.423" 0.25 0.49 1.23 1.85 2.46 5.32
1/2" 0.546" 0.15 0.30 0.74 1.11 2.62 3.87
3/4" 0.742" 0.08 0.16 0.40 1.08 1.79 2.64
1" .957" 0.05 0.10 0.39 0.79 1.30 1.92
1-1/4" 1.278" 0.03 0.05 0.27 0.55 0.91 1.34
1-1/2" 1.5" 0.02 0.04 0.22 0.45 0.74 1.09
2" 1.939" 0.02 0.04 0.16 0.33 0.54 0.80
2-1/2" 2.323" 0.02 0.03 0.13 0.26 0.43 0.63
3" 2.9" 0.01 0.02 0.10 0.20 0.33 0.48
4" 3.826" 0.01 0.02 0.07 0.14 0.23 0.34
6" 5.761" 0.005 0.01 0.04 0.08 0.14 0.20

 

Approximate Pressure Drop (PSI) per 1 Foot of line length – Tubing

Size I.D. 2fps 4fps 10fps 15fps 20fps 25fps
3/8" x 0.049" wall 0.277" 0.61 1.22 3.04 4.56 6.08 7.60
1/2" x 0.065" wall 0.37" 0.31 0.63 1.57 2.35 3.13 6.19
3/4" x 0.109" wall 0.532" 0.18 0.35 0.88 1.32 2.92 4.32
1" x 0.120" wall 0.76" 0.08 .16 0.39 1.06 1.76 2.60
1-1/4" x 0.120" wall 1.01" 0.04 0.09 0.37 0.74 1.23 1.82
1-1/2" x 0.120" wall 1.26" 0.03 0.06 0.28 0.56 0.93 1.37



Conclusion
By using the information supplied in this tech tip and selecting the proper line sizes for your hydraulic equipment you will enjoy better performance and longer life from your hydraulic components.

1.9    3.8    9.5    14.2    18.9
 
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