weight, specific volume, viscosity, volatility, and other
fluids, specific weight is expressed in pounds per cubic
properties of the fluid.
foot.
The flashpoint of a liquid is the temperature at
The specific volume of a substance is the volume
which the liquid gives off enough vapors to ignite
that is occupied by a unit weight of the substance. For
momentarily, or flash, when a flame is applied. A
most shipboard fluids, the specific volume is expressed
hydraulic fluid with a high flashpoint is desirable
in cubic feet per pound.
The specific gravity of a substance is the ratio
between the weight of that substance and the weight of
The fire point of a liquid is the temperature at which
a standard substance where both are measured under
a liquid gives off enough vapors to ignite and continue
standard conditions of pressure and temperature. For
to bum when exposed to a spark or flame. A desirable
solids and liquids, the standard substance used for
hydraulic fluid requires a high tire point as well as a
comparison is pure water. Pure water has a specific
high flashpoint.
gravity of 1. Therefore, a substance lighter than water
will have a specific gravity that is less than 1. At the
You will find more information on the
same time, a substance heavier than water will have a
characteristics of fluids in Fluid Power, NAVEDTRA
specific gravity that is greater than 1. Specific gravity
12964.
is an important property for most petroleum products.
As a rule, the specific gravity of petroleum products is
PIPING SYSTEM DESIGN
expressed in degrees API, according to a scale
established by the American Petroleum Institute using
You should have some knowledge of the principles
the hydrometer scale reading.
used to design and lay out piping systems. The
information given in this chapter is general in nature.
The viscosity of a fluid is a measure of its resistance
Detailed information can be found in contract
to flow. A fluid has a high viscosity if it flows
specifications and in NAVSEA plans and drawings.
sluggishly. An example is cold molasses. A fluid that
flows freely, like water, has a low viscosity. Gases and
All shipboard piping systems have some corrosion
vapors have lower viscosities than liquids. The
caused by the fluids they carry, which act upon the metal
viscosity of liquids will vary a great deal. In general,
of the pipe. You can minimize internal corrosion by
fuel oils and lubricating oils have high viscosities.
using piping material that will resist the corroding effect
Raising the temperature of a fluid will lower the
of the fluid being carried. You can prevent external
viscosity, while lowering the temperature will raise the
corrosion if you keep the outer surfaces dry and
viscosity.
properly painted (except for brass and copper pipe).
The viscosity index of an oil is a number that
The design, material, dimensional allowances,
indicates the effect of temperature changes on the oil's
installation procedures, and safety codes for piping
viscosity. An oil that becomes thin at a high
systems are governed by military standards and
temperature and thick at a low temperature has a low
specifications. The following sections deal with some
viscosity index. An oil that has relatively little change
important aspects of piping system design.
in viscosity with various changes in temperature has a
high viscosity index.
PIPE SIZE
The volatility of a liquid refers to the ease with
The size of pipe to be used in a system is based on
which the liquid will vaporize or evaporate. If a liquid
the pressure drop as determined by the available
is both volatile and flammable, it must be handled with
pressure and the flow requirements of the system. The
great care to prevent a fire or explosion. Gasoline is a
velocity used in the calculations usually is left to the
good example of a liquid that is both volatile and
judgment of the designer. However, special operating
flammable.
considerations may place limitations on the allowable
The operating conditions of a piping system are
velocity. For example, the velocity of seawater is
important because they have a definite effect on the
restricted to a maximum of 15 feet per second to
fluid carried by the system. Pressure and temperature
minimize the effect of erosion. Table 15-4 lists
determine the physical state of a substance; that is,
acceptable water velocities and flows used in piping
whether it is solid, liquid, or gas. Pressure and
system designs.
temperature also have definite effects on the specific
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