All-plastic air feeder pipe

DETAILED DESCRIPTION There are two important parameters that affect moisture protection for air feeder pipes, namely the permeability coefficient of the pipe material and the size of the pipe.
The permeability coefficient provides a measure of the ability of a material to transmit water vapor and/or liquid water through its thickness.
Systems generally tend to reach a state of equilibrium.
In an air pipe system, water vapor on the outside wall of the pipe seeks to cross into the pipe to come to equal concentration on both sides of the pipe.
The rate at which water crosses over into the pipe is known as the water transmission rate.
As previously discussed, polyethylene is a naturally porous material.
Its porous qualities are further amplified by air feeder systems because of the propensity of the system to achieve an equilibrium.
That is, in an air feeder pipe system the air placed into the pipe is essentially "bone dry.
" The air outside the pipe on the other hand may contain significantly more moisture.
Therefore, there is a natural tendency of the water outside pipe to cross over into the pipe.
This is exacerbated by the volume of air moving through pipe because, as the air is blown through the pipe, there is a tendency to pull even more water vapor into the pipe than would naturally cross over into the pipe.
Turning now to FIG.
1, there are shown commercially available feeder pipe materials along with their permeability coefficient at 25.
degree.
C.
and their published unit cost as of September 1998.
LDPE is shown to have the largest permeability coefficient of all the materials explored during my work.
Specifically, the permeability coefficient is 90.
times.
10.
sup.
-10 cm.
sup.
3 /cm.
sup.
2.
multidot.
s.
On the other hand, LDPE is the least costly and has the lowest tensile modulus--55 to 172 MPa--of the materials shown.
As previously discussed, the cost of the material is of particular import given the large number of pipes to be replaced; thus LDPE is particularly attractive from a cost standpoint