Environmental Engineering Reference
In-Depth Information
R
r
R = Bend radius for curved hose
r = Bend radius for straight hose
figure 4.20 Bend radius measurement.
4.11.2 factors governing hose selection
The amount of
pressure
to which a hose will be exposed is one of
the important factors governing hose selection. Typically, pressures fall
into any of three general groups:
•
<250 psi (low-pressure applications)
•
250 to 3000 psi (medium-pressure applications)
•
3000 to 6000
+ psi (high-pressure applications)
Note:
Some manufacturers have their own distinct systems for rating
hose pressure; we cannot assume that a hose rated as a “low-pressure”
hose will automatically be useful at 100 or 200 psi. It may, in fact, be
built for pressures not to exceed 50 psi, for example. Therefore, when-
ever we replace a particular hose, we must ensure that the same type of
hose with the same pressure rating as the original hose is used. In high-
pressure applications, this precaution is of particular importance.
In addition to the pressure rating of a hose, we must also consider,
for some applications, the
vacuum rating
of a hose which refers to suc-
tion hose applications in which the pressure outside the hose is greater
than the pressure inside the hose. It is important, obviously, to know
the degree of vacuum that can be created before a hose begins to col-
lapse. A drinking straw, for example, collapses rather easily if too much
vacuum is applied; thus, it has a low vacuum rating. In contrast, the
lower automobile radiator hose (which also works under vacuum) has a
relatively higher vacuum rating.
4.11.3 standards, Codes, and sizes
Just as they have for piping and tubing, authoritative standards
organizations have devised standards and codes for hoses. Standards
and codes are safety measures designed to protect personnel and equip-
ment; for example, specifications are provided for working pressures,
