PUMPS, VALVES, & FANS

1. PUMPS, VALVES, & FANS …Moving fluids

2. Objectives • Comprehend the basic construction and application of valves used • Comprehend the basic operation and application of different pumps • Know Bernoulli’s principle, the concept of pressure, & Net Positive Suction Head • Be familiar with operation and application of centrifugal & axial fans

3. Valves • Def’n: 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

4. 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

5. 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

6. Globe Valve

7. 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

8. Gate Valve

9. 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

10. Butterfly Valve

11. 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

12. Swing-check Valve

13. 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

14. 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

15. 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

16. Pumps

17. Pumps • Def’n: 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

18. BERNOULLI’S THEOREM • The Bernoulli equation is a special statement of the general energy equation • Work added to the system is referred to as pump head (hP) • Losses from the system are referred to as head loss (hL) • Pressure (lbf/in2) is a form of work • Strictly Mechanical Energy so we get the equation: P1 + PE1 + KE1 + WK = PE2 + KE2 + WKFRIC + P2

19. Pressure Head • Head • The vertical distance between two horizontal levels in a liquid • A measure of the pressure exerted by a column or body of liquid because of the weight of the liquid • Since a pump may be installed above, at, or below the surface of the source of supply, the pump must be able to overcome the net static head in order to pump from one elevation to another • Equal to Z + P/

20. Pressure Head NET STATIC HEAD STATIC DISCHARGE HEAD STATIC SUCTION PRESSURE PUMP

21. Velocity Head • Head required to impart velocity to a liquid • Equivalent to the vertical distance through which the liquid would have to fall to acquire the same velocity • Equal to V2 / 2g

22. Friction Head • The force or pressure required to overcome friction is obtained at the expense of the static pressure head • Unlike velocity head, friction head cannot be “recovered” or reconverted to static pressure head • Thermal energy is usually wasted, therefore resulting in a head loss from the system

23. Pumps – Bernoulli’s Theorem • Pressure head: measure of fluid’s mech. PE • Velocity head: measure of fluid’s 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.

24. Components of Pumps • Drive mechanism (steam, electric, gear) • Pump shaft • Impeller or piston • Casing

25. 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)

26. Positive Displacement Pump

27. 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 -> fluid accelerated as it travels outward & then enters volute • Propeller: uses prop inside casing to move fluid -> not used much in Navy

28. Centrifugal Pump

29. Pumps • Jet pumps: • Bernoulli’s principle and no moving parts • Velocity Head vs. Pressure head hin + vin2/2 = hout + vout2/2

30. Jet Pump • Types: • Eductor - used to pump liquids • Ejector - used to pump gases

31. 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 • Hpa N2 • W a N3

32. Reciprocating Pump Characteristic Curve N2 = 2 N1 N1 N2 hP (ft) . V (gpm)

33. PUMPS • Centrifugal: • Parallel pumps: V2 = 2V1 2 pumps HP HP2 = HP1 1 pump GPM V

34. PUMPS • Series (called staging): 2 pumps HP2 = 2HP1 HP V2 = V1 1 pump GPM V

35. Net Positive Suction Head • Def’n: 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

36. Net Positive Suction Head • Need enough pressure on the suction side so that the pump does not reduce pressure @ the eye to cause P < Psat • If P < Psat, water flashes to vapor causing damage to the pump • What are possible means of providing NPSH to prevent cavitation?

37. NET POSITIVE SUCTION HEAD • Need enough pressure on the suction side so that P < Psat. If P < Psat, water flashes to vapor causing damage to the pump. pump

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

39. Fans

40. Questions? Questions?