Tag Archive: pipe

Conduit calculations (pressure losses, velocity)

Pressure losses in the conduit

Pressure losses in the conduit

These calculations can help you to estimate the pressure losses, and flow velocity in the conduit (hose, pipe or tube) and check/correct conduit ID.

Calculations Notes:

  • The recommended flow velocity in conduits you can find at the article Recommended flow velocity.
  • The assumption: pressure losses on elbows, fittings at calculated conduit is zero.
  • Height difference between IN and OUT points needs to calculate hydrostatic pressure what will be added to pressure losses, if IN point is below OUT (use positive value), or subtracted from pressure losses, if IN point is upper than OUT (use negative value). Use value “0” if height difference can be neglected.
  • To find Darcy friction factor there are different formulas used:

Read the full article

Flushing of the pipes and tubes

To do pipe flushing correctly we need to provide the special conditions to create turbulent flow. This is required to remove particles from the surface inside spindle tubes. For that we need:

  1.  High velocity of the flushing fluid (not be less than 2 to 3 m/sec. = 106 ft./sec.)
  2.  High temperature of the flushing fluid (a minimum temperature should be 140°F = 60°C)
  3.  Low viscosity of the flushing fluid (in the 10 to 15 cSt range at 104°F = 40°C)
  4.  The pressure of the flushing fluid should be held to a minimum 3 to 5 bar (22 to 73 psi), measured downstream from the flushing circuit, before the return line filter and sampling port
  5.  The flushing time to be 30 min.

Next good references about flushing I found in the internet and want to share:

ID, OD and Dash size


  • What is dash size?

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Dash size is the common method used to refer to the diameter of a hose or tube in 1/16″ increments.

For hoses this is a value for Inside Diameter, or I.D. For example, -6 hose would indicate a hose with inside diameter of 6/16″ – or 3/8″.

For tubes this is a value for Outside Diameter, or O.D. For example, a -10 tube would indicate a tube with an outside diameter of 10/16″ – or 5/8″.


By the way, dash sizes do not correspond to the exact hose inside dimension. Actual ID’s are smaller.

There are couple examples how to mark piping size at the schematic using dash size:



So, if you found at the drawing, for example, (-6) size, this means:

  • For Hose: Internal Diameter is approx. 3/8″
  • For Tube: Outside Diameter is 3/8″, therefore an Internal Diameter will be much smaller.

This is why sizes of tube and pipe have to be selected accurately, especially if you are going to connect them (for example, trough bulkhead fitting). Otherwise, you can get different flow rate and extra pressure drop in the line with smaller size.