2.
Operating Characteristics of Pumps. Pumping mechanisms can be broken
into two major categories: positive displacement pumps and kinetic pumps.
The positive displacement of fluids is the principle behind positive
displacement pumps.
The most common types of positive displacement pumps
are reciprocating and rotary pumps.
a. Reciprocating pumps are similar in theory to reciprocating engines.
A piston is used to move fluid into a cylinder on the downstroke then move
the fluid out of the cylinder on the upstroke. Reciprocating pumps provide
high suction lift and high pressure for small quantities of flow as the
pistons move up and down.
b. Rotary pumps use a screw-type device to trap fluids in the cylinder
and force it out of the chamber. This type of pump is used with gasoline or
other low viscosity fuels when high suction lift is required.
The rotary
pump provides a smooth, even flow.
c. The most common type of kinetic pump is the centrifugal pump.
Centrifugal pumps depend on centrifugal force for their operation.
Centrifugal force acts on the body moving in a circular path, tending to
force it farther away from the axis or center point of the circle described
by the path of the rotating body.
(1) In a centrifugal pump, the power plant turns an impeller which
creates centrifugal force in the pump housing and forces fuel out of the
pump. Major advantages to centrifugal pumps are fewer moving parts; smooth,
non pulsating flow; and a much higher capacity than positive displacement
pumps.
One of the disadvantages of centrifugal pumps is that it has a
relatively lower head capacity than positive displacement pumps and the head
capacity is based on the design of the impeller.
(2) Centrifugal pumps are often classified by their stages. A stage
simply refers to the number of impellers on the pump. A one-stage pump has
one impeller and a two-stage pump has two impellers.
To increase the
pressure of the pump, another impeller or stage must be added.
Most Army
pumps are single stage. Such as the 6-inch, single-stage, 600-and 1,250-GPM
self-priming pump (IPDS).
The Army's multistage pumps are: the 1,400-GPM
pump is a six-inch two-stage pump used as a booster pump and 800-GPM
mainline pump for IPDS, which is a three stage pump.
3.
Conversion of PSI to FTH. FTH is defined as the measure of pressure
in terms of the height in feet of a column of a given fuel. To measure this
pressure, we need a standard.
This standard has been developed using the
one PSI gauge. The measure used as our standard was determined by using a
square inch column of water at a constant 60F. As depicted, 1 PSI is equal
to 2.31 feet. We use this measurement as our constant. The gages on pumps
are rated in PSI. To determine certain information, we may need to convert
PSI into FTH. The formula for converting PSI to FTH is:
QM5201
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