1. Positive Displacement Pumps
Prepared by
Singh Pritish Ashok
( )

2. Classification of Positive Displacement Pumps

3. Positive Displacement Pump

4. Reciprocating Pumps
Piston Pump

5. Radial Piston Pump

6. Reciprocating Pumps Swept volume =
No. of strokes per second × area of piston × length of stroke
Volumetric efficiency =
Ratio of actual discharge to swept volume. Usually 90%.
Air vessel :
- At pump discharge.
To even out the flow in discharge line.
Compressed air dilivers liquid to discharge when discharge decreases at the end of the stroke.
Reduces Friction.

7. Reciprocating Pumps Diaphragm Pumps
- For handling of corrosive & toxic liquids.
- Piston or plunger working in non corrosive fluid which actuates the diaphragm.
- Diaphragm made up of metal or rubber or plastic.
- Pneumatically actuated pump uses plant air.

8. Rotary Pump - External gear
No valve for these pumps.
Does not need priming
Discharge rate is independent of pressure.
Employed for handling high viscosity liquids,
Teeth on each gear may be two, four or more.

9. Centrifugal Vs Reciprocating Pump
Characteristics
Centrifugal Pump
Reciprocating Pump
Construction
Simple because of
less number of parts
Complex because of
more number of parts
Weight/discharge ratio
Less
More
Suitability
Smaller heads but
large discharge
Higher heads but
low discharge
Floor area requirement
Wear and tear
Maintenance cost
Liquid with solid suspension
Can handle
Cannot handle
Speed
Higher speed
Cannot run at high speed
Mode of delivery
Continuous
Pulsating
Air vessel requirement No
Yes
Operation
Simple
Much care is needed
Priming
Required
Not required
Efficiency

10. Pump Selection
Liquid properties pH, specific gravity, viscosity, temperature corrosive nature, aeration, solids in suspension, etc.
Pump properties type of pump, flow rate, NPSH, capacity, materials of construction, economic life, etc.

11. Mono Pump It can handle liquids of any viscosity.
Operate in moderate pressure ranges.
Used for feeding slurries containing higher proportion of solids.
Higher the pressure, longer the rotor and stator.

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

13. Fans

14. Cycloidal/Lobe/ Roots blower
It is positive displacement blower. Capacity upto 7 m3/s & 90 kPa.
Principle same as gear pump.
Delivers high volume at less pressure.
Shape of lobes are epicycloid or hypocycloid to ensure seal between high pressure side and low pressure side.

15. Nash Hystor/ Liquid piston type of Rotary Blower
- Positive displacement blower.
- Liquid piston type rotary blower.
- Constant supply of sealing liquid is necessary.
- Separator used in discharge line to minimize carry over of entrained liquid.
- Discharge pressure : 20 psi
- Offered as single stage unit for pressure differential upto 75 psi.

16. Centrifugal Blower Working on same principle of centrifugal pump.
Handles compressible fluid.
Casing is narrower, impeller diameter larger.
Impeller is surrounded by diffuser. It converts kinetic energy into pressure energy.
Develop pressure of 275 kPa to 700 kPa when built multistage.
Speed : 3500 rpm
Recent design to operate at more than rpm.
Turbo blower compresses 250 kPa.

17. Vacuum Service Rotary vacuum pumps-Liquid ring type
Steam jet ejectors.
Vapour from process equipment is sucked and entrained by steam. Then carried into
Venturi shaped diffuser.
Vapours along with steam are finally discharged through ejector.
Handles large volume of vapours at low pressures.

18. 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

19. Types of Valves Two basic groups: Special types:
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

20. 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

21. Globe Valve

22. 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

23. Gate Valve

24. Butterfly Valve

25. 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

26. Swing-check Valve

27. 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

28. 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

29. 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