PUMPS, VALVES,

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PUMPS, VALVES, FANS
Moving fluids
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Objectives

• Comprehend the basic construction and application
  of valves used
• Comprehend the basic operation and application of
  different pumps
• Know Bernoullis principle, the concept of
  pressure, Net Positive Suction Head
• Be familiar with operation and application of
  centrifugal axial fans

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Valves

• Defn devices which control the amount and
  direction of fluid flow in piping systems
• Typically made of bronze, brass, iron, or steel
  alloy
• Components
• - Valve body - Packing - Disc - Packing
  gland/nut
• - Seat - Stem - Bonnet - Wheel

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Types of Valves

• Two basic groups
• Stop valves - used to shut off or partially shut
  off the flow of fluid ( ex globe, gate, plug,
  needle, butterfly)
• Check Valves - used to permit flow in only one
  direction (ex ball-check, swing-check,
  lift-check)
• Special types
• Relief valves
• Pressure-reducing valves
• Remote-operated valves

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Stop Valves

• Globe Valves
• Most common type of stop valve
• Used in steam, air, water, oil lines
• Disc attached to valve stem rests against seat to
  shut off flow of fluid
• Adv Used for throttling
• Disadv flow resistance

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Globe Valve
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Stop Valves

• Gate Valves
• Used when there must be straight-line flow of
  fluid w/ min. resistance
• Gate usually wedge-shaped or a vertical disc
• Adv No flow restrictions
• Disadv poor throttling

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Gate Valve
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Stop Valves

• Butterfly Valves
• Used in water, fuel, and ventilation systems
• Adv small, light-weight, quick-acting
• Disadv leaks early only low-flow throttle
• Ball Valves
• Similar to butterfly valves
• Normally found in seawater, sanitary, trim and
  drain, and hydraulic systems

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Butterfly Valve
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Check Valves

• Controls direction of flow
• Operated by flow of fluid in pipe
• Types
• Swing check - disc moves through an arc
• Lift check - disc moves up and down
• Ball check - ball is located at end of stem and
  lifts to allow flow

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Swing-check Valve
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Relief Valves

• Used to protect piping system from excessive
  pressure
• Opens automatically when fluid pressure becomes
  too high (pressure acts against spring pressure)
• Relieving pressure set by an adjusting screw

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Pressure-reducing Valves

• Used to automatically provide a steady, lower
  pressure to a system from a higher pressure
  source
• Used in air, lube-oil, seawater, and other systems

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Remote-operated Valves

• Valves that allow operation from distant stations
• Types
• Mechanical - uses reach rods and gears
• Hydraulic - uses fluid and piston set up
• Motor - uses and electric or pneumatic motor
• Solenoid - uses coil and core mechanism to open
  or close on an electric signal

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Pumps
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Pumps

• Defn device that uses and external power source
  to apply force to a fluid in order to move it
  from one place to another
• Must overcome
• (1) frictional forces from large quantities of
  fluid
• (2) difference in static pressure between two
  locations
• Must provide any velocity desired

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Pumps Bernoullis Theorem

• Pressure head measure of fluids mech. PE
• Velocity head measure of fluids mech. KE
• Friction head measure of energy lost that heats
  fluid
• Z1 P1/r V12/2g Z2 P2/r V22/2g (U2
  U1) W Q
• q wshaft (h2 h1) (v22 v12)/2 g(z2
  z1)
• Z/z fluid height P fluid pressure r fluid
  density
• V/v fluid velocity U internal energy W/w work
• Q/q heat transferred h enthalpy g grav.
  acceleration
• BOTTOM LINE Total energy within the control
  volume is constant under SS conditions.

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Components of Pumps

• Drive mechanism (steam, electric, gear)
• Pump shaft
• Impeller or piston
• Casing

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Types of Pumps

• Positive Displacement
• Fixed volume of fluid is displaced during each
  cycle regardless of static head/pressure pumping
  against
• Uses either a piston, gear, or screw type
  (reciprocating, rotary gear, rotary screw, etc)

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Positive Displacement Pump
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Pumps

• Non-positive Displacement volume of fluid is
  dependent on static head/pressure
• Centrifugal impeller inside a case (called
  volute). Impeller is a disc w/ curved vanes
  mounted radially (like a paddle wheel)
• Suction is the Eye -gt fluid accelerated as it
  travels outward then enters volute
• Propeller uses prop inside casing to move fluid
  -gt not used much in Navy

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Centrifugal Pump
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Pumps

• Jet pumps
• Bernoullis principle and no moving parts
• Velocity Head vs. Pressure head

hin vin2/2 hout vout2/2
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Jet Pump

• Types
• Eductor - used to pump liquids
• Ejector - used to pump gases

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Pump Characteristic Curves

• Pump Parameters
• N pump speed, RPM
• V volumetric flow rate, GPM
• Hp pump head (discharge pressure), psig
• P power required, Hp
• Centrifugal Pump Laws
• V a N
• Hp a N2
• W a N3

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Positive Displacement Pumps
N1
N2
N2 ____
Hp
GPM
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Centrifugal Pumps

• Parallel Pumps

V2 ____ Hp2 ____
Hp
2 Pumps
1 Pump
GPM
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Centrifugal Pumps

• Series pumps (called staging)

V2 ____ Hp2 ____
Hp
2 Pumps
1 Pump
GPM
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Net Positive Suction Head

• Defn that pressure required at the suction of a
  pump to prevent cavitation
• So what is cavitation?
• - the formation of bubbles due to low
  pressure area and the subsequent collapse upon
  migration to a high pressure area
• Cavitation causes noise and damage

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Net Positive Suction Head

• Need enough pressure on the suction side so that
  the pump does not reduce pressure _at_ the eye to
  cause P lt Psat
• If P lt Psat, water flashes to vapor causing
  damage to the pump
• What are possible means of providing NPSH to
  prevent cavitation?

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Fans

• Same Principle as Non-positive displacement pumps
• Types
• Centrifugal majority used for compressors
• Axial (like propeller) cooling fans

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Fans
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Questions?
Questions?