The Nomographic Chart below will help you select the correct hose size for a given hydraulic system. The velocity of the hydraulic fluid should not exceed the range shown in the right -hand column. When oil velocities are higher than recommended in the chart, the results are turbulent flow with loss of pressure and excessive heating. Higher velocities may be used if the flow of hydraulic fluid is intermittent or for only short periods of time.

Velocity of hydraulic fluid in suction lines should always fall within the range recommended to assure efficient pump operation.

The following example will help you to use this chart:

Determine the hose assembly size needed to carry 10 gallons of oil per minute and figure the velocity of the oil through the hose assembly. The assembly is to be used in a pressure line and the flow will be continuous.

Locate the flow, 10 gallons per minute (left-hand column), and velocity, 10 ft. per second (right-hand column), since it is near the center of the recommended range. Lay a straightedge across these two points. The straightedge crosses the center column nearest to the 5/8 ° hose assembly. Keeping the straightedge on 10 gallons per minute in the left-hand column, cross the center column at the 3/4 ° assembly, the 5/8 ° assembly and the 1/2 ° assembly. Reading the right-hand column, the straightedge crosses it at 7.5, 10.3 and 16 ft. per second, respectively. Since 7.5 and 10.3 are within the recommended velocity range for pressure lines, either a 3/4 ° or 5/8 ° hose assembly is required.

Suction hose problems are solved in a similar manner, except that the recommended velocity range for intake line (right-hand column) is used.

Selecting the Right Hose Size
With this nomograph, you can easily select the correct I.D. size,
Desired Flow Rate (GPM) and Recommended Velocity (FPS).
If you know any two factors, you can determine the third.

The chart below is based on this formula:

To use this nomograph:
1. Pick the two known values.
2. Lay a straightedge to intersect the two values.
3. Intersection on the third vertical line gives you value of that factor.

Area (sq. in.) = Flow Rate (GPM) x 0.3208 / Velocity (ft./sec.)

EXAMPLE:
A flow rate of 4GPM is obtained through a pressure hose with a 1/2 ° I.D. A line would intersect the two values and cross the Velocity line at "6.5" indicating 6.5 FPS.