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Tech Profiles > Improve Sewer Hydraulics With HOBAS Sliplining

Improve Sewer Hydraulics With HOBAS Sliplining

Hydraulics is typically an important consideration when planning pipeline rehabilitation. When sliplining is the chosen method, a slight diameter decrease will result. However, because of the much better flow characteristics of HOBAS liner pipe, normally the rehabilitated line’s hydraulics are improved relative to its existing condition.
Hydraulic Calculator
Manning’s Equation for Open Channel Flow:
Solved for Two Simultaneous Pipe Conditions,
on the Same Slope:

Insert Your Conditions:
n1 Manning’s coefficient of the liner pipe  
n2 Manning’s coefficient of the host pipe  
D1 Inside diameter of the liner pipe inches
D2 Inside diameter of the host pipe inches
Relative Flow: Q1/Q2 =
Flow Capacity Recovery*: =
* Flow capacity recovery over 100% is an increase in the flow capacity of the pipeline.

The parameters that effect the changed hydraulics are the host and liner pipes’ Manning’s “n”, diameter, and slope. Since the slope is unchanged, the relative flow capacity is computed as follows:

(QHOBAS / QExisting) = (nExisting / nHOBAS) (DHOBAS / DExisting)(8 / 3)

The n value of existing sewers varies widely, perhaps from 0.013 to 0.024 or higher. Due to corrosion, off-set joints, sliming, and other deterioration, a likely value for aged sewers is at least 0.018. The n value for new HOBAS pipes has been measured at 0.009. After several years of service (sliming, etc.), one agency determined an n value of 0.011.
The chart below shows the ratios of flow capacity of the HOBAS liner (Q HOBAS) to the host pipe (Q Existing) for various diameter combinations and ranges of Manning’s “n”. A ratio of greater than one indicates improved flow capacity after lining with HOBAS, while a value below one means a reduced flow capacity after the rehabilitation. A 1.1 ratio is a 10% flow capacity increase. A 0.9 ratio is a 10% flow capacity decrease.


  • HOBAS Diameters are nominal for 36 psi pipe stiffness
  • Existing Sewer assumed full sized, Nominal diameter = ID
  • FL = Flush Joint. In tight fit cases, it may be required to utilize a flush joint. The ID’s of the flush joint are nominal for the typical minimum flush joint pipes.
  • HOBAS 84″ nominal size is based on the 87.0 OD mold.
Sliplining rehabilitation of sewers with HOBAS pipes provides many benefits. Not only is the flow capacity frequently increased, but the host pipe is structurally reinforced, corrosion is stopped, and leakage is eliminated.
To enjoy the many benefits of sliplining rehabilitation, specify and use HOBAS pipes on your next project.