BLM National Training Center HYDRAULIC DESIGN. BLM National Training Center FACTORS AFFECTING DESIGN...
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BLM National Training Center HYDRAULIC DESIGN. BLM National Training Center FACTORS AFFECTING DESIGN o SEASON OF USE o QUANITITY OF WATER NEEDED o WATER
BLM National Training Center FACTORS AFFECTING DESIGN o SEASON
OF USE o QUANITITY OF WATER NEEDED o WATER SOURCE PRODUCTION
LIMITATIONS o ROUTE o GEOLOGIC LIMITATIONS o FISCAL LIMITATIONS o
DEPTH OF BURY o MANUAL VS. AUTOMATIC
Slide 3
BLM National Training Center STATIC HEAD Static pressure is the
pressure that is exerted by a liquid or gas, such as water or air.
Specifically, it is the pressure measured when the liquid or gas is
still, or at rest. Pressure head is a term used in fluid mechanics
to represent the internal energy of a fluid due to the pressure
exerted on its container. It may also be called static pressure
head or simply static head (but not static head pressure).
Slide 4
BLM National Training Center Total Dynamic Head (TDH) is the
total equivalent height that a fluid is to be pumped, taking into
account friction losses in the pipe. Pressure head is a term used
in fluid mechanics to represent the internal energy of a fluid due
to the pressure exerted on its container. If the water Is moving it
may also be called dynamic pressure head or simply Dynamic head
(but not dynamic head pressure).
Slide 5
BLM National Training Center FRICTION LOSS o Friction loss
refers to that portion of pressure lost by fluids while moving
through a pipe, hose, or other limited space. o The amount of
friction loss (pressure loss) is due to four conditions: 1.The
velocity (speed) of the flow. 2.Diameter of the pipe. 3.Length of
the pipe. 4.Roughness of the pipe.
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BLM National Training Center Let's take a look at a pump curve,
the common way of showing a centrifugal pump's performance. Let's
take a look at a pump curve, the common way of showing a
centrifugal pump's performance. The size of the pump, 1-1/2 x 3 - 6
is shown in the upper part of the pump curve illustration. Note
that the size number 1-1/2 x 3 - 6 indicates that the pump has a
1-1/2 inch discharge port, a 3 inch suction port, and a maximum
nominal impeller size of 6 inches. This type of nomenclature is
common, with some companies putting the 3 in the first position
instead of the 1-1/2. In either case, standard procedure is that
the suction port is the larger of the first two numbers shown and
the largest of the three numbers is the nominal maximum impeller
size.
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BLM National Training Center Also in the upper right hand
corner notice that the curve indicates performance at the speed of
3450 RPM (a common electric motorspeed in 60 hz countries). All the
information given in the curve is valid only for 3450 RPM.
Generally speaking, curves which indicate RPM to be between 3400
and 3600 RPM are used for all two pole (3600 RPM nominal speed)
motors applications. look at a pump curve, the common way of
showing a centrifugal pump's performance. The pump's flow range is
shown along the bottom of the performance curve. Note that the
pump, when operating at one speed, 3450 RPM, can provide various
flows. The amount of flow varies with the amount of head generated.
As a general rule with centrifugal pumps, an increase in flow
causes a decrease in head.
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BLM National Training Center performance. The left side of the
performance curve indicates the amount of head a pump is capable of
generating. Notice that there are several curves which slope
generally downward as they move from left to right on the curve.
These curves show that actual performance of the pump at various
impeller diameters. For this pump the maximum impeller diameter is
shown as 6 inches and minimum is 3 inches. Impellers are trimmed in
a machine shop to match the impeller to the head and flow needed in
the application.
Slide 11
BLM National Training Center below. The point on the curve
where the flow and head match the application's requirement is
known as the duty point. A centrifugal pump always operates at the
point on it's performance curve where its head matches the
resistance in the pipeline. For example, if the pump shown above
was fitted with a 6 inch impeller and encountered 100 feet of
resistance in the pipeline, then it would operate at a flow of
approximately 240 gallons per minute and 100 feet of head. It is
important to understand that a centrifugal pump is not limited to a
single flow at a given speed. Its flow depends on the amount of
resistance it encounters in the pipeline. To control the flow of a
centrifugal pump it is normally necessary to restrict the discharge
pipeline, usually with a valve, and thus set the flow at the
desired rate. Note: Generally speaking, do not restrict a pump's
flow by putting a valve on the suction line. This can cause damage
to the pump!
Slide 12
BLM National Training Center AIR/GAS PROBLEMS Air or gas gets
into a pipeline in several ways. These include: 1.When a pipeline
is drained, air enters the line through hydrants or any opening.
2.There are various forms of gasses in well waters. These gases can
come out of solution during pipeline operation. Some wells have
more serious gas problems than others. 3.If the water level in a
well or other source falls below the pump intake, air is drawn into
the pipeline by the pump. 4.In gravity systems, air can be drawn
into the pipeline when water surface falls below the pipeline
entrance. In some live streams there can also be air bubbles
entrapped in the water. 5.When you have a gravity line and the
velocities in down hill sections exceed the rest of the pipeline
velocities.
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BLM National Training Center RELEASING AIR FROM PIPELINE
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BLM National Training Center AIR IN LOW HEAD GRAVITY PIPELINES
o Air locks are a frequent problem in very low flow, low pressure
pipelines. An example of this type of system is a spring fed
installation. In this case the velocity of water is very low. Air
bubbles do not get pushed out, even if the summit in the line is
only one pipe diameter above the rest of the line. o The solution
for air lock problems can be either of the following: Install an
open air vent at all summits in the line. Install the pipe so there
are no summits in the line. Carefully lay out the pipe so it is on
either a constantly increasing or decreasing grade.
Slide 15
BLM National Training Center NRCS recommendation for very low
pressure pipelines, experience indicates that minimum pipe diameter
should be: 1.1-1/4 inch nominal diameter for grades over 1.0
percent. 2.1-1/2 inch nominal diameter for grades from 0.5 to 1.0
percent. 3.2 inch nominal diameter for grades from 0.2 to 0.5
percent. 4.For grades less than 0.2 percent, gravity flow systems
are not recommended. Mike Montgomery recommendation: 1.Try and
standardize your pipeline pipe size. 2.If you have grades less than
0.2 percent control the grade.
Slide 16
BLM National Training Center AIR CONTROL IN HIGH HEAD, LONG
PIPELINES There are two ways to resolve air problems in high
pressure pipelines: Minimize the number of summits in the line by
meandering the pipeline along the contour to avoid high points.
There is a point where the extra cost of additional pipeline length
makes this a non-cost effective approach. Install air valves at
summits to control the entry and exhausting of air.
Slide 17
BLM National Training Center There are three types of functions
that air valves perform: 1. When a pipeline is emptied, air must
enter the line some place. If provisions are not made for entry of
air, a vacuum can be created in the pipeline. This can lead to
collapse of the pipe or at least breaking of the water column,
which creates gas or water vapor pockets in the pipeline. Although
it is unlikely that the small diameter pipe in stockwater lines
will collapse due to vacuum, it is a bad design practice to allow
significant vacuum to develop in the pipeline. It is therefore
important to have a vacuum relief mechanism at significant high
points in the line.
Slide 18
BLM National Training Center 2. When an empty pipe is filled
with water, air in the line must be released in large volumes. This
can be done by leaving the hydrants open. But what if the hydrants
are closed? Air pressure will build up in the pipeline. When a
hydrant or float valve is opened, high pressure air will escape and
then, when water hits the end of the line, waterhammer will
probably occur. For adequate system protection, there must be a
mechanism to automatically release large volumes of air from the
pipeline during filling. For best results, the mechanism should be
located at all significant summits in the line. There are three
types of functions that air valves perform:
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BLM National Training Center 3. During operation of the
pipeline, air bubbles and other gasses come out of solution and
buildup as gas bubbles at summits in the line. There are usually
also remnants of the large volumes of air present immediately after
filling. If the summit is high enough, this air will never push on
through the line. Gases may eventually buildup to the point where
the flow rate is seriously reduced or flow may even stop. It is not
possible to predict how serious a problem this may be when
designing a pipeline. There are three types of functions that air
valves perform:
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BLM National Training Center 1.A line that has worked for years
will sometimes slow down or stop. The usual culprit is air in the
line. 2.Adequate air handling equipment should always be designed
into a system at the time of initial installation. 3.In high
pressure, moderate flow systems, there are frequently many small
undulations in the ground surface and a few large humps. Trial and
error on typical long stock lines in Montana has led to the
conclusion that we can usually get away with not installing air
vents or valves on summits that are less than ten feet high. So in
most cases, it is recommended that air handling equipment be
installed on all summits of ten feet or more, at the end of the
pipeline and at the first high point of any kind past the pump. (as
a minimum every 2000 ft. mjm) AIR VENT LOCATION:
Slide 23
BLM National Training Center EXAMPLE 1, LOW HEAD GRAVITY SYSTEM
Figure 9.1 illustrates the profile for a very low head system. The
pipeline originates at a spring box and terminates at a stock tank.
An overflow is built into the stock tank. There is not float valve
at the tank and the entire spring flow goes to the tank. A
gate-type valve could be installed at the spring box to throttle
the flow or shut it off when water is not wanted. A valve at the
tank allows drainage of the pipeline during non-use. The pipeline
is buried below the frost line.
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Slide 27
BLM National Training Center Questions for exercise 1: 1. What
is the static pressure at Station 10+00, 15+00, 25+00, 30+00, and
tank station? 2.What diameter pipe should be used? 3.Calculate the
pressure rating of the pipeline pipe for this project. 4.If the
spring is flowing 5 gpm, and the water at the tank if flowing 5
gpm, what is the dynamic head at the tank? This question could be
called a trick question. 5.If the spring will flow 10 gpm, and the
water tank has a flow restrictor of 5 gpm what is the dynamic head
at the tank?