Environmental Engineering Reference
In-Depth Information
sizes, and material requirements. The working pressure of a hose, for
example, is typically limited to one fourth, or 25%, of the amount of pres-
sure required to burst the hose. Let's look at an example. If we have a
hose that has a maximum rated working pressure of 200 psi, it should
not rupture until 800 psi has been reached, and possibly not even then.
Thus, the importance of using hoses that meet specified standards or
codes is quite evident.
4.11.3.1 Hose Size
The parameter typically used to designate hose size is its inside
diameter (I.D.). With regard to the classification of hose, ordinarily a
dash numbering
system is used. Current practice by most manufactur-
ers is to use the dash system to identify both hose and fittings. To deter-
mine the size of a hose, we simply convert the size in 16ths; for example,
a hose size of 1/2 in. (a hose with a 1/2-in. I.D.) is the same as 8/16 in. The
numerator of the fraction (the top number, or 8 in this case) is the dash
size of the hose. In the same way, a size of 1-1/2-in. can be converted to
24/16 in. and so is identified as a -24 (pronounced “dash 24”) hose. By
using the dash system, we can match a hose line to tubing or piping sec-
tion and be sure the I.D. of both will be the same. This means, of course,
that the nonturbulent flow of fluid will not be interrupted. Based on I.D.,
hoses range in size from 3/16 in. to as large as 24 in.
4.11.3.2 Hose Classifications
Hose is classified in a number of ways; for example, hose can be clas-
sified by type of service (hydraulic, pneumatic, corrosion-resistant), by
material, by pressure, and by type of construction. Hose may also be clas-
sified by type. The three types include metallic, nonmetallic, and rein-
forced nonmetallic. Generally, terminology is the same for each type.
4.11.3.3 Nonmetallic Hose
Relatively speaking, the use of hose is not a recent development.
Hoses, in fact, have been used for one application or another for hun-
dreds of years. Approximately 100 years ago, after new developments in
the processing of rubber, hoses were usually made by layering rubber
around mandrels. Later, the mandrel was removed, leaving a flexible rub-
ber hose. These flexible hoses tended to collapse easily, but they were
an improvement over the earlier types. Manufacturers later added layers
of rubberized canvas. This improvement gave hoses more strength and
gave them the ability to handle higher pressures. Later, after the develop-
ment of synthetic materials, manufacturers had more rugged and more
corrosion-resistant rubber-type materials to work with. Today, neoprene,
nitrile rubber, and butyl rubber are commonly used in hose. Current man-
ufacturing practice is not to make hoses from a single material; instead,
various materials form layers in the hose, reinforcing it in a variety of
ways for strength and resistance to pressure. Hose manufactured today
usually has a rubber-type inner tube or a synthetic (e.g., plastic) lining
