Hydraulic Principles
1
Overview
• The information provided in this presentation should be
fully understood to ensure success in those non-typical,
P/C fluids handling applications. Proper selection of
Moyno® progressing cavity pumps is dependent upon
understanding Fluid Dynamics and Hydraulic Principles,
i.e., Net Positive Suction Head conditions [(available vs.
required) and stated as NPSHA or NPSHR)], friction loss
calculations and horsepower sizing.
• Moyno credits the Cameron Hydraulic manual for basic
definitions. Because this manual typically deals with
centrifugal pumping applications, we have clarified some
of these definitions to better relate with our progressing
cavity pumping principles.
2
Overview
• Pumping…To move a liquid against gravity, as with a
pump, work must be expended. A pump may actually
raise the liquid, force it into a pressure vessel, or merely
give it enough head to overcome pipe friction.
• No matter what the service required of a pump, all forms
of energy imparted to the liquid in performing this service
must be accounted for in establishing the work
performed.
• In order that all these forms of energy may be
algebraically accounted for, it is customary to express
them all in terms of ‘head’ expressed in “feet of liquid” or
“feet of fluid”.
3
Hydraulic Principles
• Hydraulics deal with the behavior of liquids
at rest or in motion.
• Proper selection of Moyno® progressing
cavity pumps is dependent upon
understanding :
–
–
–
–
–
NPSHA
Friction loss calculations
Horsepower sizing
Viscosity
Fluid rheology
4
Liquid Flow
•
•
•
During passage through a pipe, the flow of a liquid is said to be
laminar, or turbulent, depending upon the velocity of the fluid through
the pipe, the size of the pipe, and the viscosity of the liquid.
Laminar flow is defined as a streamline flow with consistent velocity of
a fluid near a solid boundary.
Turbulent flow is defined as a fluid flow in which the velocity at a given
point varies erratically in magnitude and direction.
5
• A Reynolds number is used to calculate the line loss exhibited by a
liquid; Moyno’s Computer Aided Pump Selection (CAPS) program
will take this into consideration for you.
• In fluid mechanics, the Reynolds number is the ratio of inertial forces
to viscous forces.
• Calculating the Reynolds number will help in determining whether
the flow is turbulent or laminar. The main application where the
Reynolds number and turbulence is considered relates to the
settling of solids in a slurry.
• Laminar flow occurs at low Reynolds numbers, where viscous forces
are dominant, and are characterized by smooth, constant fluid
motion, while turbulent flow on the other hand occurs at high
Reynolds numbers and is dominated by inertial forces, which tend to
produce random eddies, vortices and other flow fluctuations.
6
Liquid Flow
Where...
VD
R=
v (ft.)
V = Average velocity (ft./sec.)
D = Average internal pipe diameter
v = Kinematic viscosity pumped fluid
(ft.2/sec.)
•
•
•
•
•
(ex. Kin. Visc. of water = .00001211 ft.²/sec.)
For values of “R” less than 2,000, the flow is considered LAMINAR.
For values above 4,000, it is said to be TURBULENT.
Any value between 2,000 and 4,000 is considered the CRITICAL ZONE
where the flow is generally said to be turbulent for the purpose of friction
loss or pressure drop calculations, because turbulent flow results in higher
friction losses than laminar flow.
The Reynolds number, although important to know, is not often used when
selecting Moyno progressing cavity pumps. We do suggest, however, you
remain familiar with the principles and terms.
Again, the main application where R and turbulence is considered, relates
to the settling of solids in a slurry.
7
Example
• An example application is illustrated in the next
two slides showing the CAPS screens when
utilizing the: Calculating Pipe Loss feature.
• Example: Water moving through 100 feet of 3
inch diameter schedule 80 pipe, at a flow of 100
GPM and at a velocity of 5 feet / second, has a
Reynolds number of 109,034.479, and “head
loss” more commonly stated as 7.859 psi (see
CAPS Pipe Friction Loss chart below).
8
Reynolds Number in Caps
Reynolds
Number is
used to
calculate
the Line
Loss in
CAPS
Reynolds
Number For
Water at 5
ft/sec
Note: 5 ft/sec is the Velocity & Turbulence required
for acceptable CIP Cleaning
9
Rule Of Thumb
• Use Sch 80 to
approximate
sanitary
tubing ID
• Increasing
viscosity
decreases
turbulence &
Reynolds
Number
10
Fluid Principles
11
Viscosity
• In moving liquids, resistance to flow is called
Viscosity.
• Viscosity plays an important role when
selecting Moyno progressing cavity pumps
because you need to understand how the fluid is
going react in the pump i.e. at the suction and in
the pumping elements.
• It is vital to proper pump selection, and all efforts
must be made to obtain accurate viscosity data
during the sizing process.
12
Viscosity
• Viscosities of most liquids vary with changes in
temperature.
• Viscosity of moving fluids can change depending
upon the extent to which the liquid is agitated or
sheared.
• However, pressure changes normally have no
effect on the viscosity of a fluid.
• The following chart illustrates various viscosity
ratings from zero to a million centipoise.
13
Viscosity
14
Effects of Viscosity
• The more viscous a fluid, the slower the pump should operate in
order to permit the fluid to enter into the cavity.
• Even at reduced speeds, the pump may not develop 100%
volumetric efficiency and this must be accounted for in the selection
process.
Cavity
only half
full
• Loss of fill efficiency as it relates to viscosity vs. maximum pump
speed for any given element
•1 CPS = Above 1800 RPM
•100 CPS = 700 RPM
15
•1000 CPS = 150 RPM
•10,000 CPS = 30 RPM
Effects of Viscosity
• Most fluids shear thin to a level well below their static viscosity
(single Brookfield point)
• Pumps are applied based on shear viscosity in a flow condition.
Moyno can provide shear rate testing free of charge
• For higher viscosity ranges, open throat style pumps are used with
auger screw on the connecting rod to enhance feed
Flights on Conrod offers
low cost auger feed
compared to other gear,
lobe or hose PD pumps
16
PEC 449
• Developed to determine Volumetric Efficiency
• Consult with your regional manager to explain its use
• CAPS utilizes a math model of PED 449 curve
17
Effects of Viscosity
• Minimum Recommended Volumetric Fill Efficiencies
• Rule of Thumb – strive to obtain these minimum levels
before moving up to the next element size
• CAPS uses the term “Intake Index”, where 0 = 0% and
10.0 = 100%
Application
1.Transfer
Efficiency
65%
2.Metering
3.Extrusion
98%
18
95-100%
Viscosity
• A liquid is said to be a NEWTONIAN fluid if its viscosity is unaffected
by agitation (shear) as long as the temperature remains constant.
Examples of Newtonian fluids would be water, mineral oil or silicone.
• A liquid is Non-NEWTONIAN and also displays “THIXOTROPIC”
characteristics if its viscosity decreases as it is “sheared” at constant
temperatures. 98% of Moyno’s applications fall into this category;
examples of thixotropic fluids would be molasses, glues, paints,
coatings, and mustards.
• A fluid is Non-NEWTONIAN and said to be “DILATANT” when
agitation [putting energy into a product] of the liquid causes the
viscosity to increase. Examples of Dilatant fluids are candy
compounds and special paper clay slurries.
19
Summary
• Additional Non-Newtonian terms and their explanations
for you to be aware of are found in the definition of terms
section at the end of this chapter.
• Again, viscosities of most liquids vary with changes in
temperature, but pressure changes exerted upon them,
normally has no effect. So, the viscosity of moving fluids
will change depending upon the extent to which the
liquid is agitated / sheared and most typically affected by
flowing through a pipe at a specific velocity.
• Most liquids are Thixotropic (shear thinning) as noted in
the following Brookfield viscosity chart.
20
Most Products are Thixotropic
(Shear Thinning)
•
•
As part of Moyno’s Ultra-Serve program, we provide Shear Rate verses Viscosity testing “Free of
Charge”
Velocity used instead of Sec -1. Allows you to use for pipe loss calculations based on the pipe
shear rate.
21
System Head Calculations
22
System Head Calculations
• The pressure existing at any point in a liquid at
rest is a result of the atmospheric pressure
exerted on the surface, plus the weight of the
liquid above the specific point in question.
• This pressure is equal in all directions and acts
perpendicularly with any surface in contact with
the liquid.
• A column of liquid is called the “pressure head”
or “static head” and is normally expressed in feet
of liquid.
23
System Head Calculations
• A column of liquid is called the “pressure head”
or “static head” and is normally expressed in feet
of liquid.
• Unlike centrifugal pump applications, it is
strongly recommended that total head
calculations for the suction side be listed
separately from those on the discharge side, to
help avoid the possibility of overlooking severe
suction conditions.
• H = hd – hs (flooded suction)
H = hd + hs
(suction lift)
24
System Head Calculations
•
Static Suction Head exists when the liquid supply level is
above the pump suction centerline. This is most often
referred to as a “flooded suction”.
Static suction head (expressed in
feet) is the vertical measurement of
the liquid above the centerline of the
pump rotor and is generally a
positive head measured in feet/fluid.
Static Suction head
The total suction head is equal to the static height in feet that the liquid supply
level is above the pump suction, less all suction line losses plus any pressure
existing at the suction supply source.
25
System Head Calculations
• It should be noted that even when the
liquid supply level is above the pump
suction, the equivalent of a lift could exist if
the total suction line losses exceed the
positive static suction head.
• An example of applications where this
condition exists would be pumping from an
evaporator or de-aerator tank, in which
case there exists a vacuum effect.
26
System Head Calculations
• Static Suction Lift exists when the liquid supply
level or suction source is below the pump
suction. Total suction lift is equal to the static lift
in feet, plus all friction losses in the suction line.
Moyno pumps are able to suction lift 28 feet of
Water at Sea level.
• When the liquid supply or suction source is
above the pump suction and under a vacuum,
the equivalent of the suction lift will exist.
27
System Head Calculations
Static lift conditions are present when the liquid level on the
suction side of the pump is below the centerline of the pump
rotor.
Static Suction Lift
When discussing suction lift conditions, it is important to recognize the
vertical lift measurement is taken from the lowest level in the reservoir.
In many instances, the liquid level will vary dramatically..
28
System Head Calculations
• When the liquid supply or suction source is
above the pump suction and under a vacuum,
the equivalent of the suction lift will exist.
• Static discharge head.
• All piping and friction losses on the discharge
side of the pump including pipe, elbows, valves,
strainers, etc.
• Pressure in the discharge chamber (if a closed
vessel).
29
System Head Calculations
Static Discharge Head
Static discharge head is
the measurement,
expressed in head in feet,
from the centerline of
the pump to the highest
elevation in the
discharge system.
This figure is based upon the upper most level the fluid accumulates in
the receiving vessel.
30
System Head Calculations
Net Discharge Head
- Net Suction Head
= Total Dynamic Head (TDH)
Total Dynamic Head (TDH)
Net Discharge Head
Net Suction head
31
System Head Calculations
Net Discharge Head
+ Net Suction Lift
= Total Dynamic Head (TDH)
Net Discharge Head
Net Suction Lift
32
System Head Calculations
• The total system head or total dynamic head is equal to
the total discharge head, minus the total suction head, if
positive, or plus if a suction lift.
H = hd – hs (flooded suction)
Where...
H = hd + hs (suction lift)
H = Total system head
hd = Total discharge
hs = Total suction head
33
System Head Calculations
• Head and Pressure are interchangeable terms provided they are
expressed in their correct units. The following are key conversion
formulas for you to use when analyzing pumping systems:
PSI x 2.31
Liquid Head ( Feet ) =
Sp Gr
Head in Feet x Sp Gr
Pressure ( PSI ) =
2.31
• Sp gr =Specific gravity of the liquid.
• Pressure and friction loss calculations also play a vital role in
selecting Moyno progressing cavity pumps.
• Suction and discharge pressures must be known to ensure the
proper pump and accessory equipment is selected.
• More will be discussed on this topic in the “How to Select” section.
34
Summary
• Pressure and friction loss calculations play
an important role in properly selecting
Moyno progressing cavity pumps.
• Suction and discharge pressures must be
known to ensure the proper pump is
selected.
35
Net Positive Suction Head
• The Net Positive Suction Head (NPSH) calculation is vital when
selecting Moyno progressing cavity pumps.
• Failure to have adequate net positive suction head available in a
pumping system will result in inefficient pump operation up to and
including damage to the pump in the form of cavitation. This will
result in loss of flow and failure of the pumps Stator.
NPSH Available in
the Application
NPSH Required
by the pump
≥
+
Safety
Factor
• Per Hydraulic Institute standards - Safety Factor = 3 FT Head or 1
PSI
36
Net Positive Suction Head
• The NPSH is the total suction head in feet
of liquid less the absolute vapor pressure
(in feet) of the liquid being pumped.
• NPSH must always have a positive value
and can be calculated by using the
following equations:
37
Net Positive Suction Head
Available - NPSHa
For suction lift...
NPSHa = ha – hvpa h
hfs
st - positive
For
(flooded) suction... NPSHa = h – h + h - h
a
vpa
st
Where...
ha =
hvpa
Absolute pressure in feet of liquid on the surface of the
liquid supply level (this will be barometric pressure if
suction is from an open tank or sump, or the absolute
pressure existing in a closed tank such as an evaporator or
de-aerator).
=The
head in feet corresponding to the vapor pressure of the
liquid at the temperature being pumped.
hst = Static height in feet that the liquid supply level is above or
below the pump suction centerline.
hfs = All suction line losses in feet including entrance losses and
function losses through pipe, valves, filters, etc.
38
fs
Net Positive Suction Head
Available - NPSHa
NPSHa Example 1
Open System, 68°F Water At Sea Level
Atmospheric Pressure = 14.696 psia
Atmospheric Pressure
14.696 psia = 33.96 ft. abs.
Vapor Pressure of Water @ 68°F = 0.783
68 Degree F Water
100 gpm, 3” line, 1 cps (for suction losses, hfs)
NPSHa = ha – hvpa + hst – hfs
10 Ft.
NPSHa =33.96 - 0.783 + 10.00 - 0.236 = 42.94 Ft
39
Net Positive Suction Head
Available - NPSHa
Open System, 68°F Water At Sea Level, 10’ lift
Atmospheric Pressure = 14.696 psia
14.696 psia = 33.96 ft. abs.
NPSHa Example 2
Vapor Pressure of Water @ 68°F = 0.783
100 gpm, 3” line, 1 cps (for suction losses, hfs)
NPSHa = ha – hvpa - hst – hfs
NPSHa = 33.96 - 0.783 - 10.00 - 0.236 = 22.94 Ft
10 Ft. Lift
Atmospheric Pressure
68 Degree F Water
40
Net Positive Suction Head
Required - NPSHR
•
When sizing Moyno pumps, two values of NPSH must be considered.
•
The first is Net Positive Suction Head Required, determined by Moyno, Inc.,
and can be calculated from the performance curves provided by Moyno.
•
NPSHR figures can be
located in the upper righthand corner of all of our
standard performance
curves.
•
From the chart, the higher
the pump RPM, the higher
the NPSH required, this is
because the cavity is
opening and closing at a
much higher rate, leading to
higher entrance losses
41
Net Positive Suction Head
Required - NPSHr
• CAPS is capable of
returning the NPSHR
value for a particular
pump by entering 1 cps
into the viscosity line
• If a viscosity greater
than 1 is entered, no
NPSHr value will be
given
42
Horsepower
• The work performed in pumping or moving a liquid from one point to
another equals the required horsepower. Horsepower also depends
on the weight of the liquid being handled and the total differential
pressure being developed. The following is the most commonly
used HP formula:
• Brake HP = GPM x psi /1714
• Where…
– GPM = Gallons per minute
– psi = Pounds per square inch
– GPM should be noted as: theoretical flow + slip = actual flow
• Horsepower calculations will be discussed more thoroughly in the
“How to Select” section.
43
Definitions
The below definitions are provided for your clarification and can also be found
on the home screen of Moyno’s CAPS program under the Glossary button….
•
Liquid: A substance in that state in which its particles have enough cohesion to tend
to remain in one mass, but still are capable of moving freely among themselves upon
the application of the slightest force, the mass having, like solids, a definite volume
but, unlike solids, no definite shape.
•
Pressure: (Common Usage) – Pressure per unit area or “intensity” of compressive
stress within the liquid, above local atmospheric pressure. It is commonly expressed
as “pounds per square inch”, “kilograms per square centimeter” or “bars”.
•
Three pressure terms are commonly used in pumping opportunities … absolute,
barometric and gauge pressure.
1. Barometric Pressure -- The atmospheric pressure at the locality of the application
and varies with altitude and climatic conditions.
2. Absolute Pressure -- The pressure above absolute zero. It may be above or below
the atmospheric pressure existing at the point under consideration.
3. Gauge Pressure -- The pressure above atmospheric at the locality where it is
measured. A vacuum is a negative gauge pressure.
44
Definitions
•
Pressure Head or Head: Designates the vertical height of a static column
of the fluid that would cause the same pressure or compressive stress as
exists in the fluid mass at the point in question, also know as….Static Head.
•
Static Head: The height of a column of liquid acting on the pump suction or
discharge.
•
Atmospheric Pressure: Pressure exerted by the atmosphere, which varies
with the applications elevation, typically in the mid-west US = 14.7 PSI
•
Vacuum: The difference between atmospheric pressure at a given elevation
and some pressure below the atmospheric pressure. Usually expressed in
inches or millimeters of mercury, but can be converted to PSI, i.e. 3 inches
of mercury = 3 PSI or 155 millimeters of mercury = 3 PSI.
45
Definitions
•
Vapor Pressure: Every liquid at any temperature above its freezing point exerts a
pressure due to formation of vapor at its free surface. This pressure, known as the
vapor pressure of the liquid, is a function of the temperature of the liquid. The higher
the temperature, the higher the vapor pressure. In any pumping system the pressure
at any point should never be reduced below the vapor pressure corresponding to the
temperature of the liquid, because the liquid will form vapor which will partially
decrease liquid flow into the pump.
•
Static Suction Lift: The vertical distance, in feet, from the liquid supply level to the
pump center line, the pump being above the supply level.
•
Static Suction Head: The vertical distance, in feet, from the liquid supply level to the
pump center line, the pump being below the supply level.
•
Static Discharge Head: The vertical distance, in feet, from the pump center line to the
point of free delivery of the liquid.
•
Total Static Head: The vertical distance, in feet, between the supply level and the
discharge level of the liquid being handled.
46
Definitions
•
Friction: Measured in feet of the liquid handled, this is the equivalent head needed to overcome
the resistance of the pipe, valves and fittings in the pumping system. Friction head exists on both
the suction and discharge sides of the pump and varies with liquid flow rate, pipe size, interior
condition of the pipe, type of pipe and nature of the liquid being handled. Converting to PSI = ft/hd
X specific gravity; divided by the constant of 2.31.
•
Velocity Head: Liquid moving through a pipe at any velocity possesses kinetic energy due to its
movement. Velocity head is the distance through which the liquid must fall to acquire a given
velocity and is found from hv = v2/2g, where hv = velocity head, ft. of liquid; v = liquid velocity, ft.
per sec.; g = acceleration due to gravity = 32.2 ft. per sec2.
•
NPSH Available: A function of the system. It is the sum of the suction head or lift, friction head
and the vapor pressure of the liquid being handled.
•
NPSH Required: A function of pump design. It varies from one make of pump to the next and
with the capacity and speed of any given pump.
•
Pascal’s Law: Pressure, if extended anywhere upon a mass of liquid, (1) is transmitted with equal
intensity in all directions; (2) acts with the same force on all equal areas; and (3) acts in a direction
at right angles to those areas.
47
Definitions
• Specific Gravity: The ratio of the specific weight of a substance to
the specific weight of some standard substance. For liquids, the
standard usually employed is water.
• Barometers: The pressure gauges used to measure atmospheric
pressure.
• Newtonian Fluids: Those fluids whose viscosity depends only on
temperature and ambient pressure and are independent of the rate
of shear or the length of time the fluid is sheared.
Shear Stress
Viscosity
Shear Rate
Shear Rate
48
Definitions
•
Non-Newtonian Fluids: Those fluids whose viscosity depend not only on
temperature and ambient pressure, but may also depend on the rate of shear and/or
the length of time that the fluid is sheared.
• Types of Non-Newtonian Fluids:
A. Time Independent – the fluid can be sheared for any length of time at a constant shear
rate with no subsequent change in viscosity.
–
–
–
Bingham Plastic – Shear thinning after an initial stress is overcome.
Pseudo Plastic – Shear thinning.
Dilatant – Shear thickening.
B. Time Dependent – The fluid viscosity is affected by the length of time the fluid is
sheared.
–
–
Thixotropic – Shear thinning.
Rheopectic – Shear thickening.
C. Viscoelastic Fluids – Possess both elastic and viscous properties (bread dough is an
example).
49