1. Pumps
CM4120
D. Caspary
February, 2004

2. Outline Intro to Pumping Classifications of pumps
Positive Displacement Pump – Examples and Applications
Centrifugal Pumps – Examples and Applications
Pump Curves

3. History of Pumps
First pumps were driven by water wheels or animal powered
Water was lifted w/ paddles and dumped at a higher elevation
Over 2200 years ago in Greece, Persia, the Orient , some still in use today
Electric motor is most common machine in use today, the pump is second most common
Agriculture  Automobile  Construction  Chemical Manufacturing  Household  Hydraulic Systems  Submarines  Space Station  Zeeland to Zimbabwe
The pump is said to be one of the first complex machines in recorded history.

4. Pump Applications
Used to increase the potential and/or kinetic energy state of a fluid
Liquid – water, chemical, fuels, coolants, refrigerants, hydraulic fluids, boiler feed, condensate return, etc.
Vapor/gas – foams, air, other gases
Slurries – concrete, quarry slurries, mud for drilling, precipitates, sewage, pulp stock, etc.

5. Two Primary Classifications of Pumps
Dynamic (or Centrifugal) – Use a spinning impeller to induce centrifugal forces, increasing pressure at the discharge side of the housing.
Positive Displacement – Transfers a fixed volume of fluid thru the pump housing with each cycle of operation.
Spinning impeller increases the velocity of the fluid w/in the pump housing.
The centrifugal forces of the fluid on the pump housing cause an increase of pressure at the discharge side of the housing.
As long as there is a path for the fluid to leave the pump housing, more fluid is drawn (forced) into the suction side due to the vapor pressure of the fluid.

6. Classifications of Pumps
Overwhelming majority of all pumps are some type of Centrifugal Pump.
Lower initial cost
Reduced maintenance costs
Positive Displacement Pumps are widely used but for specific applications.
Many/most pumping applications use centrifugal pumps.
Cent pump impeller spins freely in the fluid with no mechanical surfaces contacting the pump housing.
Simple design with minimal wear parts makes for a very reliable device.
PD pumps are application specific.

7. Comparison between Positive Displacement and Centrifugal Pumps
When viscosities get high
When you need self-priming
When you need high discharge pressures
When you have a metering application where a specific volume of fluid must be delivered for each rotation of the pump shaft
When you need constant flow regardless of discharge pressure
When you want to control flow by controlling pump speed
-- use a PD pump

8. Head vs. Flow Comparison between Positive Displacement and Centrifugal Pumps
Compare PD with Cent pump
PD has constant delivery regardless of discharge head (pressure)
Cent. Pump has high capacity at low head, but flow drops off as discharge head increases.

9. Effect of Increasing Viscosity on Flow for Positive Displacement and Centrifugal Pumps
PD pumps have “slip” at low viscosity
As viscosity increases, slip is reduced and flow remains constant throughout range.
Cent pump has big performance drop off as viscosity increases above 500 SSU (light motor oil)
Can heat fluid to reduce viscosity and still use cent pump

10. Comparison of Efficiency vs
Comparison of Efficiency vs. Head between Positive Displacement and Centrifugal Pumps
PD pump efficiency is almost constant over operating range.
Cent pump will have a single best operating point where efficiency is at a peak

11. Positive Displacement Pump “Family Tree”
Many types of PD pumps

12. Types of PD Pumps – Gear Pumps
External Gear Pump
High speed
Quiet operation
Fuel, lubricants, hydraulic fluid power systems, metering
No solids
Internal Gear Pump
Non-pulsating discharge pressure
Low NPSHR
Low to moderate speed
High viscosity fluids
External gear pump
One gear is driven by motor, the other is driven by the first.
Fluid enters and travels in the cavity between the gear teeth and the pump housing to get to the discharge.
Internal gear pump
The outer cage is driven by a motor. The inner gear is driven by the cage.
Fluid travels through two paths.
Between the gaps in the cage and the outer housing.
Between the inner gear teeth and the crescent shaped divider.

13. Other Common Types of PD Pumps
Lobe Pump
No metal to metal contact
Can handle solids without damaging them
Applications are found in food processing, pharmaceutical, personal care, etc.
Diaphragm Pump
Lobe pumps are “timed so that there are no contacting parts.
Each lobe has a shaft sticking out the back side of the pump housing.
The shafts have meshing gears installed outside of the housing.
One shaft is driven by a motor. The gears keep the two lobes in the same relationship with each other.
Diaphragm pumps
Can be mechanically driven or air driven. Air driven pumps can be installed in hazardous environments without concern for electrical sparks igniting a combustible atmosphere.

14. Centrifugal Pump “Family Tree”
Pumps
Centrifugal
Positive Displacement
Single Stage
Multi-Stage
Horizontal
Vertical
Open Impeller
Closed Impeller
The other side of the pump story…
Most common centrifugal pump is the single stage, horizontal shaft, w/ a closed impeller.

15. How a Centrifugal Pump Works
Pump housing must be primed
Impeller rotates, imparting an outward velocity to the fluid – kinetic energy
Fluid velocity reaches maximum at the outside diameter of the impeller
Fluid enters the volute where it is channeled to the discharge
Housing must be filled with water for the pump to operate – “prime”
Fluid reaches a maximum pressure at the discharge side of the pump.
In the volute, velocity decreases, causing an increase in pressure.
Pressure is highest at the discharge.
If the downstream piping isn’t blocked fluid will flow.
The “cut-water” is the point where the impeller is closest to the housing.
Resistance to flow, starting at the volute, reduces velocity creating pressure energy
Vapor pressure of fluid causes new fluid to be drawn into the eye of the impeller

16. A Centrifugal Pump/Driver Installation
Discharge line
Electric Motor
Pump Housing
Coupling
Buffalo Forge pump from UO Lab showing all pump parts
Bearing Support
Suction line
External Cooling
Stuffing Box and Packing Gland

17. Single Stage, Horizontal Shaft, Closed Impeller Flowserve Pump Co.
Cut-away shows good view of bearing support, packing, housing/impeller clearances

18. Horizontal, Split Case, Single Stage Fire Pump Patterson Pump, Div
Horizontal, Split Case, Single Stage Fire Pump Patterson Pump, Div. of Gorman-Rupp
Note the pressure gages on the upstream and downstream side of pump.
Handwheel valve.
Split case pump has bearings on both side of impeller, where previous picture shows cantilevered design.

19. Vertical Pumps Carver Pump Co.

20. Horizontal, Multi-Stage Pump Cut-away

21. Types of Impellers Closed vane Open vane Open vane, cut impeller
Closed vane gives highest discharge head
Open vane handles solids
Cut impeller allows you to use the same pump for a wide range of applications (where the maximum flow and head is below that of the full-sized impeller.

22. Pump Curve for a Goulds Model HSC centrifugal pump at 3500 rpm
When selecting new pump or changing capacity of existing pumps:
Capacity for 6 impeller sizes
NPSHR
Req’d horsepower
Efficiency
Pump curve shows:
Head vs flow
Req’d HP vs flow
Efficiency vs flow
NPSHR vs flow – all at a specific RPM
Single pump curve shows data for all impellers that are available for this pump.

23. Pumping Affinity Laws
Used for estimating pump performance when changing impeller size or RPM
Q1/Q2=N1/N2
H1/H2=(N1/N2)2
P1/P2=(N1/N2)3
1-2-3 Affinity Laws:
Flow is proportional to RPM
Head is proportional to the square of RPM
Power is proportional to the cube of the RPM

24. Pump Efficiency Overall Efficiency
PP, Pump Input power, BHP
PW, Pump Output Power
Consider the efficiency of a pump/motor package.
Measure the electrical input power
Measure the water horsepower – the rate of work being done to the fluid.
To measure the pump efficiency you need to measure the torque on the pump shaft and the shaft RPM – Prony brake.
Then measure the water horspower.
PMOT, Driver Input Power

25. Pump Maintenance Seals Shaft packing vs. mechanical seals
Monitor for leaks
Bearings
Overhung vs. double support
Monitor vibration
Wetted parts corrosion
Cavitation
monitor suction-side pressure
listen for rattling

26. References Viking Pump product literature
Gorman-Rupp product literature
Goulds Pump product literature
Flowserve product literature
Carver Pump product literature
Pump Handbook, Karassik, Krutzsch, Fraser, Messina, McGraw-Hill, 1976
Viking Pump, Feb
The Engineering Toolbox, March 2004.

27. Pumping Terminology Head Gauge head (hg) Velocity head (hv)
Elevation head (Z)
Atmospheric head (hatm)
Total suction head or suction lift (hs)
Total discharge head (hd)
Total head (H)
NPSHA
NPSHR