PUMPS; The Heart of the Process
Chemical industry relies more heavily on pumps than any other piece of equipment. They are indispensable for moving fluids throughout the process.
A pump converts mechanical energy, usually supplied by an electric motor, into fluid energy by pushing the fluid along the system. All pumps operate by creating a partial vacuum at the intake
(entrance) and a mechanical force at the outlet (discharge). The resulting fluid energy may be used to increase the pressure, the velocity, or the elevation of the fluid.
Although there are many different types of pumps, they can all be grouped into two categories; positive displacement pumps and kinetic (or dynamic) pumps.
In positive displacement pumps, one cycle or revolution of the pump causes a fixed quantity or volume of fluid to pass through the pump. Theoretically, the flow of a positive displacement pump depends only on its size and speed. The size determines the amount of fluid moved per revolution and the speed determines the number of revolutions per unit time.
Kinetic or dynamic pumps, commonly called ‘centrifugal pumps’, depend not only on size and speed but also on resistance to flow in the discharge (outlet) line. As discharge resistance increases (the back pressure against the pump increases), the amount of fluid that passes through the pump decreases.
A characteristic difference of great importance is the result of pumping with a closed valve in the discharge line of a pump. Centrifugal pumps have large clearances (have space between parts) allowing slip within the pump. The output of a centrifugal pump decreases rapidly to zero against a closed valve. As a result, no damage occurs to the pump or discharge piping.
Positive displacement pumps are designed to have tight clearances (have little space between parts) that minimize slip within the pump. Operating a positive displacement pump with a closed discharge line has disastrous consequences. The discharge pressure rapidly increases against a closed valve since there is no place for the fluid to go. The pressure will continue to rise until either the pump or piping rupture.
Positive displacement pumps are the most important type in mechanical applications, e.g., pumping hydraulic fluids, however, centrifugal pumps are the workhorse of chemical manufacturing and food processing industries.
Positive displacement pumps are usually used for low-volume, medium to high pressure applications of 500 psi (3.5 MPa) and up, whereas centrifugal pumps are favored in highvolume, low-pressure applications (up to 600 psi or 4MPa). Positive displacement pumps are used where pressure is of primary concern and centrifugal pumps are favored in high volume, low maintenance applications.
Centrifugal pumps have a relatively simple design and few moving parts, so that they are less expensive to purchase and require less maintenance than positive displacement pumps.
PIPES, FITTINGS, VALVES AND PUMPS SELF STUDY UNIT Page 35 of 53

Positive Displacement Pumps
Despite the close tolerances in positive displacement pumps, a small amount of slippage occurs; the actual flow is slightly less than theoretical. The actual flow rate divided by the theoretical flow rate is the ‘volumetric efficiency’. Most positive displacement pumps have a volumetric efficiency between 85 and 98 percent.


Positive displacement pumps are generally rated by their maximum operating pressure and their output in gallons per minute at a given drive speed. For example, a pump may be nominally rated as a 50 gpm (13.6 m 3 /h) unit. Under no load conditions, the pump can deliver considerably more than 50 gpm, but less than 50 gpm at its rated operating pressure.
Positive displacement pumps can be subdivided two types depending on construction; i.e., reciprocating and rotary. Examples of these two types are shown below.
Positive Displacement Pumps
Reciprocating Pumps Rotary Pumps
Diaphragm pumps
Piston pumps
Plunger pumps
Gear pumps
Screw pumps
Vane pumps
PIPES, FITTINGS, VALVES AND PUMPS SELF STUDY UNIT Page 36 of 53

Reciprocating Pumps
Diaphragm Pumps contain a flexible membrane which is pushed and pulled back and forth. As the diaphragm moves backwards, liquid is sucked into a chamber, then as the diaphragm flexes forward, the liquid discharges from the chamber. The direction of flow is determined by check valves. One of the main advantages of diaphragm pumps is that the driving mechanism is completely isolated from the fluid being pumped, so the diaphragm pump is particularly advantageous where leakage and/or contamination of a process fluid cannot be tolerated.
Tapflo
Diaphragm Pump diaphragm (flexible membranes)
Warren Rupp
Diaphragm Pump
A diaphragm pump usually has adjustments for speed and strokelength. It can pump at high pressures and so is commonly used for fluid injection applications. A familiar example is as a liquid chlorine pump for swimming pools.
Diaphragm pumps are subject to check valve wear and are particularly prone to failure if solids, abrasives, or dirt are present in the liquid being pumped.
PIPES, FITTINGS, VALVES AND PUMPS SELF STUDY UNIT Page 37 of 53

Piston and Plunger Pumps have a back-and-forth or up-and-down motion. A connecting rod drives a piston within a cylinder. Check valves commonly direct flow in one direction. inlet check valve outlet check valve
This old-style, manual water pump was used do draw water from wells. The reciprocating motion of the piston with the aid of check valves produces alternating vacuum and pressure strokes.
All reciprocating pumps produce a pulsating flow; a pattern of flow, no flow. Some reciprocating pumps utilize double pistons that are operated in opposite timing. This minimizes the pulsation effect.
A piston pump is commonly used to pump fluids through liquid chromatographs (LC units).
Students (this means you). Go into Lab 403 and look at the two piston pumps on the LC unit.
Next time this instrument is operating look at the movement of the pistons.
Fluid Metering Inc.
LC piston pump
Dynex ballcheck piston pump
PIPES, FITTINGS, VALVES AND PUMPS SELF STUDY UNIT Page 38 of 53

Rotary pumps differ from reciprocating pumps in that no check valves are required. They rely on close tolerances between the moving and stationary parts to minimize leakage. The close tolerances limit operating speeds. Rotary pumps are best for clean, moderately viscous fluids.
High discharge pressures are possible but flow rate are generally not much higher than 100 gpm.
Gear pumps are the most widely used type of rotary pump. They are made with a drive gear a nd an idle gear, the teeth of which interweave while rotating. These are called ‘external gear pumps ’ or ‘spur gear pumps’. Fluid is carried between the teeth of the gears as they turn.
Some clearance between parts is necessary to prevent seizing at elevated temperatures. As a result a small amount of slippage is unavoidable. However, volumetric efficiency can range from 80 to 95%. drive gear
External (Spur)
Gear Pump idle gear
Lear Romec spur gear pump
Gear pumps with only a few (usually three) rounded teeth are called ‘lobe pumps’. The large space between lobes produces much higher fluid displacement than in the gear pump, hence higher flow rates
.
Netzsch Toronado
Lobe Pump
PIPES, FITTINGS, VALVES AND PUMPS SELF STUDY UNIT Page 39 of 53

Another variation of a gear pump, called an ‘internal gear pump’, in which the two gears are concentric, one within the other.
Haight Internal
Gear Pump
Gear pumps are commonly used to pump fuels to oil fired furnaces, paints, varnishes, inks and heavy oils.
An example of a gear pump familiar to the laboratory is a
‘peristaltic pump’. Rotating lobes squeeze fluid through flexible
(silicone) tubing analogous to the swallowing action (peristalsis) in human alimentation. rotating lobes
Clark Peristaltic
Pump
Screw pumps have one, two, or three helical rotors (screws) within a close-fitting chamber. The only moving part is the screw, which is driven by a motor. Fluid trapped in the spaces between the flights (threads) of the screw are pushed forward with little pulsation or agitation as the screw turns. Screw pumps are commonly used in the food processing industry where materials of very high viscosity can be easily pumped. Even finely divided solids (fine sand) can be pumped with screw pumps.
Netzsch Screw
Pump
PIPES, FITTINGS, VALVES AND PUMPS SELF STUDY UNIT Page 40 of 53

Vane pumps contain a rotating shaft (eccentrically located), to which sliding vanes are attached. The vanes slide in and out as the shaft rotates within the housing and this transports fluid through the pump. By changing the position of eccentricity between the shaft and the housing, the amount of liquid displaced per revolution is changed. In this manner the vane pump acts as a variable displacement pump. rotor sliding vane
Lear Romec
Vane Pump
The volumetric efficiency of a vane pump is generally about 90%. They can operate in high pressure applications (e.g., 2500 psi) and are frequently used to supply fluid pressure for hydraulic machinery.
PIPES, FITTINGS, VALVES AND PUMPS SELF STUDY UNIT Page 41 of 53

Kinetic or Dynamic Pumps
The parts of a centrifugal pump include an inlet or suction port, a pumping chamber shaped like a volute (a spiral), a drive shaft with impellor and an outlet or discharge port.
Large clearances allow slip, resulting in a fluid flow that decreases with increasing resistance to flow in the discharge line. As a result volumetric efficiency of centrifugal pumps may only reach 60%.
In operation, liquid enters the suction port, located in the centre of the volute. The liquid is forced outwards at high velocity in a spiral fashion by the impellor blades.
Because clearances are not tight within these pumps, centrifugal pumps are not self-priming. As such, if these pumps are not primed they must be located below the level of liquid to be pumped. If any air or vapors find their way into the volute, pumping action may be halted or severely reduced.
Although it is generally safe to throttle the discharge of a centrifugal pump, the intake should not be throttled when liquid is being pumped. The reduced pressure at the intake may cause vaporization of some of the fluid, resulting in bubbles of vapor becoming trapped in the volute. The differential forces on the impellor (against vapor and liquid) may cause noise, severe vibration and rapid erosion of the impellor. The phenomenon of vapor entrapment in the impellor of a pump is called
‘cavitation’.
Centrifugal pumps can deliver high flow rates at low to moderate pressure with a variety of liquids. They are quiet, low cost, low maintenance and can be run continuously. diffuser vanes impeller
Clark Magnetic Drive
Centrifugal Pumps
Impeller of Logos
Centrifugal pump
Note the diffuser vanes in the volute of a centrifugal pump. discharge
PIPES, FITTINGS, VALVES AND PUMPS SELF STUDY UNIT Page 42 of 53

All About Pumps Website
The operation of some of these pumps may be difficult to visualize. The student is encouraged to visit the ‘All About Pumps’ website and after logging in, review the pumps listed below in the
‘Glossary of Pumps’. Most have animations to aid visualization.
Look at the following types of pumps in the glossary…
Crescent pumps (Internal gear),
Bilge pumps (manual piston pump),
Archimedes screw,
Diaphragm (for auto fuel pumps),
Double diaphragm, page 3 (see flexible membranes),
Duplex pumps (piston pumps),
Fish tank diaphragm air pump,
Force pump (piston pump),
Gear pump,
Gear pump - 2 lobe,
Gear pump – 3 lobe,
Hand pump (for lotions, skin creams),
Impeller mechanism,
Lift pump (for wells),
Peristaltic pump (for labs),
Piston pump,
Progressive cavity pump (screw pump),
Quimby screw pump,
Radial piston pump,
Simplex (piston),
Squeeze bulb (lab style),
Vacuum pump (piston),
Vane pump,
Volute pump (centrifugal),
Water gun Super Soaker.
PIPES, FITTINGS, VALVES AND PUMPS SELF STUDY UNIT Page 43 of 53

Answer the following questions
1. Briefly explain why pumps are important.
2. Describe/explain the meaning of a ‘positive displacement’ pump.
3. Explain why the volumetric efficiency of positive displacement pumps is much higher than dynamic pumps.
4. If a valve is closed in the discharge line of a pump, explain what would happen if the pump were… a) a centrifugal pump b) a positive displacement pump
5. What applications are positive displacement pumps normally used for?
6. What applications are centrifugal pumps normally used for?
7. If a positive displacement pump is rated at 25 gpm, will the pump deliver this flow under all conditions? Explain.
8. List three kinds of reciprocating pumps a) b) c)
PIPES, FITTINGS, VALVES AND PUMPS SELF STUDY UNIT Page 44 of 53

9. What is the characteristic flow produced by reciprocating pumps?
10. In addition to the diaphragm, what other part(s) is essential to the operation of a diaphragm pump?
11. List three kinds of rotary pumps a) b) c)
12. How does a rotary pump differ from a reciprocating pump
13. List three kinds of gear pumps a) b) c)
14. What type of flow is produced by a rotary pump?
15. Briefly describe the flow of liquid through a centrifugal pump
16. State two important characteristics of centrifugal pumps which result from the large clearances in these pumps a) b)
17. What is meant by cavitation in a centrifugal pump?
What causes cavitation and what are its effects?
18. State three advantages of centrifugal pumps over positive displacement pumps. a) b) c)
Check your answers by rereading the pump information. If you are unsure about some of the answers after rereading the section, please ask the instructor.
PIPES, FITTINGS, VALVES AND PUMPS SELF STUDY UNIT Page 45 of 53

STEP 6:
WORKBOOK PIPES, FITTINGS, VALVES AND PUMPS
CUMULATIVE SELF TEST
Assess what you have learned. Answer the following questions. e)
1. In the space provided name the valve shown. a) b) c) f) k) i) j) g) l) d) h)
PIPES, FITTINGS, VALVES AND PUMPS SELF STUDY UNIT Page 46 of 53

2. In the space provided name the fitting shown. Describe the method of joining. a) b) c) d) e) h) f) i) g) j) k) m) l)
PIPES, FITTINGS, VALVES AND PUMPS SELF STUDY UNIT Page 47 of 53

3. With reference to the table of data for PVC plastic pipe data
Nominal
Tube Size
(in)
1/8
Schedule
Number
O.D.
(in)
0.405
Wt./Ft.
(lbs)
1/4
3/8
1/2
3/4
1
1 ¼
1 ½
2
40
80
40
80
40
80
40
80
40
80
40
80
40
80
40
80
40
80
0.540
0.675
0.840
1.050
1.315
1.660
1.990
2.375
Wall
Thickness
(in)
0.068
0.095
0.088
0.119
0.091
0.126
0.109
0.147
0.113
0.154
0.133
0.179
0.140
0.191
0.145
0.200
0.154
0.218
0.043
0.055
0.074
0.094
0.100
0.129
0.150
0.150
0.199
0.259
0.295
0.382
0.400
0.527
0.478
0.639
0.643
0.884 a) b) c) d)
Wt. H
2
O/ft
(lbs)
0.025
0.016
0.045
0.031
0.083
0.061
0.132
0.101
0.230
0.186
0.374
0.311
0.647
0.555
0.882
0.765
1.452
1.279
Calculate the weight of a 20.0 ft length of 2 in schedule 80 PVC pipe
Calculate the weight of water contained in 145 ft of 1½ in schedule 80 PVC pipe.
Calculate the ID (inches) of 2 in schedule 40 PVC pipe
Calculate the volume of water (US gal) contained in 225 ft of the 2 in schedule 40
PVC pipe.
PIPES, FITTINGS, VALVES AND PUMPS SELF STUDY UNIT Page 48 of 53

4. In the following table, put a check mark in the correct column opposite each statement. Do not guess as ½ mark is subtracted for each incorrect mark.
Positive
Displacement
Pumps
Kinetic
Pumps has high volumetric efficiency can pump fluids at very high pressure preferred for highest flow rates has lower maintenance costs produces pulsating flow produces steady flow best for continuous service discharge rate varies more with resistance to flow are not self priming each revolution moves a specific volume of fluid closing its discharge will not harm these pumps has very close tolerances (tight fitting parts) has a volute-shaped pumping chamber
5. If a positive displacement pump is rated at 25 gpm, will the pump deliver this flow under all conditions? Explain.
6. State three advantages of centrifugal pumps over positive displacement pumps. a) b) c)
7. List 3 different kinds of reciprocating pumps a) b) c)
PIPES, FITTINGS, VALVES AND PUMPS SELF STUDY UNIT Page 49 of 53

d)
7. Write the name of the type of pump in the space provided a) b) e) g) c) f)
PIPES, FITTINGS, VALVES AND PUMPS SELF STUDY UNIT Page 50 of 53

WORKBOOK PIPES, FITTINGS AND VALVES
STEP 6 CONT’D: SELF TEST - ANSWERS
1. Give yourself one mark for each correct answer a) gate valve b) globe valve c) ball valve d) plug valve e) needle valve f) ball valve g) butterfly valve h) rupture disc i) angle valve j) check valve k) diaphragm l) globe valve
2. Give yourself 2 marks for each answer that is both correct and complete a) threaded return bend b) butt welded reducing coupling c) solvent welded 45

elbow d) threaded union e) threaded cross f) threaded close nipple g) soldered copper tee h) threaded straight coupling i) compression fitting j) flare fitting k) threaded bushing l) 2 flanges and a gasket m) threaded pipe plug.
PIPES, FITTINGS, VALVES AND PUMPS SELF STUDY UNIT Page 51 of 53

3. For a), b) and c) give yourself 1 mark for each correct answer and another mark each if the answer has the correct number of sig figs. For d) give yourself 3 marks for the correct answer and another mark for the correct number of sig figs a) 17.7 lb b) 111 lb c) 2.067 inches d) 39.2 US gallons
4. (13 marks) The correct answer is indicated by a check mark . Do not guess as ½ mark is subtracted for each incorrect answer.
Positive
Displacement
Pumps
Kinetic
Pumps has high volumetric efficiency can pump fluids at very high pressure preferred for highest flow rates has lower maintenance costs produces pulsating flow produces steady flow best for continuous service discharge rate varies more with resistance to flow are not self priming








 each revolution moves a specific volume of fluid closing its discharge will not harm these pumps has very close tolerances (tight fitting parts) has a volute-shaped pumping chamber




5. (2 marks) The actual output of a positive displacement pump will be greater than the advertised rate
(> 25 gpm) under no load, but less than the rated output under high load, e.g., < 25 gpm when raising a fluid to a high elevation, i.e., high back pressure.
6. (3 marks) Advantages of kinetic pumps over positive displacement include: a) lower purchase price, b) lower maintenance costs, c) can be run continuously, and they are quieter
PIPES, FITTINGS, VALVES AND PUMPS SELF STUDY UNIT Page 52 of 53

7. (7 marks) The types of pumps shown are: a) vane b) kinetic c) diaphragm d) lobe e) internal gear f) piston g) screw
The final step (STEP 7) of this Self Study Unit is to write an actual test. This will be scheduled during the final exam week of the semester.
PIPES, FITTINGS, VALVES AND PUMPS SELF STUDY UNIT Page 53 of 53