Positive displacement pumps Flashcards
Can positive displacement pumps handle entrained air and vapor in the pumping medium?
yes;
the high suction lift capabilities allow this
True or false:
With positive displacement pumps, as the system pressure rises so to does the internal leakage, resulting in a gradual reduction of volumetric efficiency.
true
What formula is used to calculate volumetric efficiency of a positive displacement pumps?
volumetric efficiency = (actual volumetric output ÷ theoretical volumetric output) x 100
What are the 2 classifications of positive displacement pumps?
- reciprocating
- rotary
When the prime mover on a piston or plunger reciprocating pump is powering a crankshaft, this is called a:
power pump
When the prime mover on a piston or plunger reciprocating pump is steam or compressed gas acting directly on the piston rod or plunger, this is called a:
direct-acting pump
What type of pump would be used to generate extremely high pressures for cleaning, pressurizing systems, or hydraulic testing?
piston and plunger reciprocating pumps
Can piston and plunger reciprocating pumps be used to meter liquids into pressurized vessels and pipelines?
yes
What are the 3 main advantages of piston and plunger reciprocating pumps?
- low cost
- mechanical simplicity
- produce high pressures
What are 2 disadvantages of piston and plunger reciprocating pumps?
- cannot handle abrasive liquids
- must not run dry
What could happen if a piston or plunger reciprocating pump ran dry?
it could compromise the packing, resulting in leakage and failure
What is the stroke of a piston or plunger reciprocating pump?
the distance the plunger or cylinder moves
Is a plunger reciprocating pump a single or double acting pump?
single
Can a piston reciprocating pump be a double acting pump?
yes
Can piston or plunger reciprocating pumps be self priming?
yes;
- to be self priming they must have small clearance volumes (space between the piston or plunger when fully extended and the cylinder head)
This type of pump is similar to a piston or plunger pump in the pumping motion, but instead uses a flexible membrane to create the suction and discharge.
diaphragm pump
Why are diaphragm pumps suitable for use with toxic or hazardous liquids?
the membrane completely isolates the liquid from the rest of the pump
Which type of reciprocating pump would be used if the liquid being pumped consists of mud and solids up to the size of the openings in the check valves?
a diaphragm pump
Can a diaphragm pump run dry?
yes;
- it can run dry without damage to the pump
True or false:
Diaphragm pumps are self priming, and once primed can handle very high suction lifts.
true
What are the 2 main drawbacks of diaphragm pumps?
- small output capacity (20 GPM max)
- pulsating flow
What is a popular material for the flexible membrane in diaphragm pumps?
PTFE (Teflon)
Are rotary pumps considered continuous flow pumps?
no;
- although the flow is smooth, it is not considered continuous
Are twin rotor and circumferential piston pumps self priming?
yes
Twin rotor and circumferential pistons pumps have ____________ pressure capabilities.
medium
What happens when twin rotor and circumferential piston pumps are used with low viscosity liquids?
there is internal leakage past the sides of the rotor, making them uneconomical
What kind of viscosity fluids should twin rotor and circumferential piston pumps be used with?
medium to high viscosity liquids
Can twin rotor and circumferential pistons pumps be used with abrasive liquids, such as slurries?
no
Pressures in rotary pumps are normally unbalanced, due to the fact that the discharge port is opposite the suction port. What effect does this have on the pump?
creates a pressure differential across the rotor, resulting in high radial loads on the bearings
This type of rotary pump uses an offset rotor with sliding vanes turning in a concentric housing.
unbalance vane pump
This type of rotary pump uses a concentric rotor with sliding vanes turning in an elliptical housing, producing two pumping chambers diametrically opposite each other.
balanced vane pump
This type of rotary pump has a separate pressure chamber ring or cam ring that can be used to vary the amount of eccentricity.
variable vane pump
This type of rotary pump uses an oval rotor turning inside a concentric housing.
an external vane pump
This type of pump uses a rotor with two or more lugs mounted on the periphery to compress the tube against the housing, pushing the liquid through the tube.
flexible tube pump
What is an advantage of flexible member pumps (tube, liner, vane)?
they completely isolate the pumping medium from the pump parts, making them good where contamination of the medium must not occur
What types of industry are flexible member pumps (tube, liner, vane) found in?
medical, food, and chemical
True or false:
Flexible member pumps (tube, liner, vane) are not well suited for pumping abrasive and viscous fluids.
false;
they are well suited for pumping abrasive and viscous solids
True or false:
Flexible member pumps (tube, liner, vane) cannot run dry short periods.
false;
they can run dry for short periods
This pump uses an eccentric rotor to compress a flexible liner against the housing and uses a divider between the discharge and inlet to prevent liquid from leaking back to the inlet.
flexible liner pumps
This pump uses a rotor with flexible vanes rotating inside a concentric housing with a cam shaped insert in the housing that compresses the vanes and forces the liquid out of the discharge port.
flexible vane pump
This type of pump has a sinusoidal impeller made up of two complete sine curves dividing into four separate compartments.
sine pump
This type of pump uses long rotors with external threads to trap liquid in a series of pockets in the threads and move it axially form inlet to discharge.
screw pumps
True or false:
Screw pumps may have one, two, or three rotors or screws.
true
In what 2 industries are screw pumps widely used?
- pharmaceutical
- wastewater treatment
When an elastomeric insert is used, what type of pump can tolerate abrasives better than any other type of rotary pump?
screw pumps
True or false:
Screw pumps can tolerate high viscosity liquids and slurries.
true
True or false:
Screw pumps have a pulsating flow delivery.
false;
they have constant flow delivery
These types of pumps combine the high pressure capabilities and efficiency of piston pumps with the compactness of rotary pumps.
axial and radial piston pumps
Where are axial and radial piston pumps found in industry?
in hydraulic systems requiring high speeds and high pressures
What effect does changing the swashplate angle on an axial or radial piston pump have on the pump?
changes the length of the stroke = changes the output
- as with piston pumps, output = stroke volume x RPM
What three pump designs are considered reciprocating pumps?
- piston
- plunger
- diaphragm
In a reciprocating plunger pump, what is the end of the plunger threaded in to?
the crosshead
With a reciprocating plunger pump, what purpose does the crosshead serve?
it stabilizes the movement of the plunger
True or false:
A plunger pump can be mounted both vertically and horizontally.
true
Plunger pumps with more than one cylinder are called:
multiplex pumps
A simplex plunger pump has _________ cylinder(s).
1
A duplex plunger pump has ___________ cylinder(s).
2
A triplex plunger pump has __________ cylinder(s).
3
With multiplex plunger pumps, why are the cranks on the plungers arranged so that plungers are on different portions of their strokes at any one time?
to dampen pulsations
- pulsations = vibration = bad
With a plunger pump, what effect does changing the thread engagement between the plunger and the crosshead have on the pump?
it will increase or decrease output by changing the stroke length, which will change the stroke volume
- this will be secured with a locknut
When used as a metering pump, in what 2 ways is the output of a plunger pump adjusted?
- variable speed drive
- adjusting the piston stroke
What is a reciprocating steam pump?
a combination of a steam engine and pump
What is the prime mover with a direct acting piston pump?
steam or compressed air
True or false:
A steam powered direct acting piston pump is a good choice for pumping product of variable viscosity and temperature due to the fact that it has infinite variability.
true;
changing the steam pressure changes the output
Are steam drive direct acting piston pumps a good choice for use in hazardous areas?
yes;
- they do not require an electric prime mover (SECTION 18)
Why must the flexible membrane in diaphragm pumps have a high diffusion strength?
high diffusion strength = prevent molecules from diffusing through the membrane
Can diaphragm pumps be pneumatically or hydraulically activated?
yes
What types of flow rates do diaphragm pumps provide?
low to medium flow rates
What type of diaphragm pump is used for very high pressures?
hydraulically activated diaphragm pump
What safety equipment is included with hydraulically activated diaphragm pumps?
two pressure limiting sensors: one overpressure and one under-pressure sensor
Which safety sensor is used on a hydraulically activated sandwich diaphragm pump to ensure that the process and hydraulic liquids don’t mix nor escape to atmosphere?
a diaphragm rupture sensor
On a diaphragm pump, what is a sandwiched membrane?
a membrane that has more than one working layers, increase it’s strength
How can the output of a hydraulically activated diaphragm pump be controlled?
by adjusting the fluid closing port adjustment knob
- this controls how much hydraulic fluid can escape out of the plunger housing, which in turn limits the stroke. the more hydraulic fluid trapped in the housing, the less stroke as the hydraulic fluid cannot be compressed
This type of diaphragm pump consists of two diaphragms connected by a common shaft.
pneumatically activated double diaphragm pump
Is a pneumatically activated diaphragm valve infinitely variable?
yes;
- only to the max level of the compressed air; if the pump pressure = compressed air pressure the pump will not work
Does a circumferential piston pump require timing gears?
yes
What is the purpose of the vane in an external vane pump?
provides the seal between the rotor and the housing as well as separates the inlet and outlet ports
This type of pump is also known as a progressive cavity pump.
flexible tube pump
This type of pump is also known as a peristaltic pump.
flexible tube pump
- also a single screw pump
Why is a flexible tube pump known as a peristaltic pump?
due to its successive wave-like or worm-like contractions
True or false:
A circumferential piston pump delivers a constant volume, pulse-free flow.
true
Why are flexible tube pumps found in industries such as medicine production?
due to their ability to isolate the fluid from contamination as it is being pumped
True or false:
Flexible liner pumps do not require shaft seals, as the product is completely separated from the moving parts by the liner.
true
True or false
A flexible liner pump is a constant volume pump.
true
This type of rotary pump uses an eccentric cam rotating within a flexible liner that squeezes the product trapped between the liner and the housing.
flexible liner pump
How can the output of a flexible vane pump be changed?
by changing out the cam
Why do flexible vane pumps not require a pressure relief valve?
the flexible nature of the vanes means that if pressure builds too high, it will push the vanes back and allow for flow back to suction, and no damage will be done to the pump
What type of pressures are flexible vane pumps limited to?
low pressures;
- this has to do with the flexible nature of the vanes, which can be pushed backwards at higher pressures
Are single rotor screw pumps considered peristaltic pumps?
yes
This type of pump is also known as a progressive or progressing cavity pump.
single rotor screw pumps
This type of pump consists of a long, corkscrew like rotor with a single external helix that operates inside a double threaded helix stator or liner.
single rotor screw pump
What can be done on a single rotor screw pump if the pump becomes obstructed?
they can be reversed in an attempt to free the blockage
True or false:
Single rotor screw pumps have a smooth output and a high volume.
true
This type of pump has two rotors with opposing screw threads.
two screw pump
Does a two screw pump require timing gears?
yes
This type of pump has a central drive rotor with a screw thread of one hand and two idler screws with threads of the opposite hands.
three screw pump
Does a three screw pump require timing gears?
yes;
- maybe, depending on the pumping medium
True or false:
Most positive displacement pumps must incorporate a relief valve on the discharge side to protect them from damage by excessive pressure.
true
What is a foot valve?
a check valve installed at the bottom or foot of a suction line
- think suction lift, keeps the pumped medium from draining back into the tank
What is an alternative to a foot valve to keep liquid in a pump?
a priming loop
What are 3 types of pulsation dampers?
- nonseparated
- bladder
- diaphragm
This type of pulsation dampener uses compressed air or inert gas to pressurize a space above the pumped liquid in a vertical cylinder.
non-separated pulsation dampener
Why must non-separated pulsation dampeners be used in low pressure applications only?
since there is no separation, in high pressure applications the compressed air would be dissolved into the liquid
- as pressure rises, so does the amount of air (or other gas) that dissolves into a liquid
This type of pulsation dampener incorporates a rubber bag inside a cylinder, which is pre-charged with gas.
bladder pulsation dampeners
What type of gas is most commonly found in a bladder type pulsation dampener?
nitrogen
This type of pulsation dampener uses a diaphragm mounted between two halves of a cylinder.
diaphragm pulsation dampeners
What precautions must be taken with a diaphragm pulsation dampener?
the membrane must be compatible with the liquid
What are two advantages of herringbone gear pumps?
- stops pulsations
- mitigate axial thrust
What are 4 types of check valves found on pumps?
- ball
- poppet
- disc
- flap types
This type of check valve allows the free passage of solids up the size of the opening between the ball and the seat.
ball check valves
This type of check valve is used for clear liquids due to the size of the port.
poppet check valve
This type of check valve components are usually made out of bronze and are only suitable for low pressures.
stem guided disc valves
This type of check valve can handle high pressures but are restricted by the wings to use with clear liquids only.
wing guided disc check valves
This type of check valve can pass solids and slurring but can only handle low pressures and are primarily used with diaphragm pumps.
flap check valve
What source of energy is available to allow liquid to enter a pump with a suction lift?
atmospheric pressure
The component in a pump that converts mechanical energy into kinetic energy is the:
impeller
True or false:
A pump converts mechanical energy into hydraulic energy.
true
True or false:
Impeller shrouds are used to stiffen the impeller vanes.
true
True or false:
Wear plates are used with open impellers.
true
True or false:
The most common type of centrifugal pump is single-stage end suction.
true
True or false:
Pumps handling hot liquids should be centerline mounted.
true
True or false:
A rigid coupling is used when the pump rotor has no separate bearings.
true
True or false:
Wet pits increase the NPSH available.
true
True or false:
Double suction single stage pumps have a single inlet.
true
True or false:
Propeller pumps can have over 20 stages.
false;
they can have 3 max
True or false:
Barrel pumps can be horizontally or vertically mounted.
true
Pumps are primed by bleeding gas off through the:
air vent
True or false:
Water hammer can be eliminated by the use of a pulsation dampener.
true
When blinding piping prior to pump removal, the blinds should be placed:
downstream of the suction valve and upstream of the discharge valve
What type of vane pumps has an oval rotor?
external vane pump
Which type of check valve is least suitable for liquids containing solids?
wing-guided disc
True or false:
Foot valves are necessary when handling viscous liquids.
false;
viscous liquids would require too much pressure with a foot valve
True or false:
Pulsation dampeners can be installed in either the suction or the discharge lines.
true
Identify the following pump:
External gear pump
Identify the following pump:
Internal gear pump
Identify the following pump:
Single lobe rotary pump
Identify the following pump:
Three lobe rotary pump
Identify the following pump:
Circumferential piston pump
Identify the following pump:
Unbalanced vane pump
Identify the following pump:
Variable vane pump
Identify the following pump:
Balanced vane pump
Identify the following pump:
External vane pump
Identify the following pump:
Flexible tube pump
Identify the following pump:
Flexible liner pump
Identify the following pump:
Flexible vane pump
Identify the following pump:
Sine wave pump rotor
Identify the following pump:
Double acting power piston pump
When it comes to positive displacement pumps, what is pulsation?
Vibration caused by the nature of the pumping action
What are the 3 methods of actuation of a diaphragm pump?
- Mechanical
- Hydraulically
- Pneumatically
What is the return mechanism on a diaphragm pump that is crank or cam activated?
A spring
Identify the following pump:
Single screw rotor or progressive cavity pump
Identify the following pump:
Two screw pump
Identify the following pump:
Three screw pump
What happens on a pneumatically actuated diaphragm pump when the pumping liquid equals the air inlet pressure?
The pump will stop pumping, as there is not enough pressure to move the cylinder
