58 Questions
What does 'Net Positive Suction Head (NPSH)' primarily depend on?
Pump performance capabilities and suction-side pipe shape
In centrifugal pumps, what does 'Hydraulic head' refer to?
The potential energy of water translated as the height of a water column
What may occur if a pump operates beyond its designed suction performance?
Cavitation
What do pump characteristic curves show changes in relative to discharge values?
Net actual head, pump efficiency, and required input power
How do single-stage volute pumps discharge liquid?
From the periphery of the impeller
What do multi-stage pumps use multiple impellers to achieve?
The required discharge head
How do single-suction and double-suction volute pumps differ in drawing in liquid?
Single-suction draws in liquid from one side only while double-suction draws in liquid from both sides
What type of ball bearing requires periodical replacement of ball bearings?
Enclosed-type ball bearing
What is one of the probable causes of pump shaft vibrations?
Excessive deviation in drive shaft and pump shaft alignment
What is one common symptom of bearing trouble?
Vibration
What accounts for almost all mechanical seal problems?
Leakage
What should be applied to the packing ring when attaching a mechanical seal?
$ ext{Lubricating oil}$
What should be conducted by injecting a liquid extracted from the high-pressure part into the sealing part to keep the sliding surface in a favorably lubricated condition and to prevent accumulation of impurities in the stuffing box?
$ ext{Flushing}$
In which method is the side surface measured with a dial gauge and the end surface with a clearance gauge?
Shaft center measuring method I
What is one of the precautions to be taken when attaching a mechanical seal?
Cleanse the sliding surface, packing ring and its ring groove using clean washing oil, taking care not to scratch or bruise them.
What should be confirmed prior to use when attaching a mechanical seal?
The turning direction is correct.
What type of liquids are rotary pumps commonly used for transferring?
Viscous liquids
How are discharge amounts in rotary pumps adjusted?
By adjusting the flow rate of the bypass line
What is the main mechanism used by gear pumps to carry liquid from the suction side to the discharge side?
Two gears of identical shape rotating in an enclosed casing
Which type of pump is designed to push out liquid by the movement of screw rotors housed in the casing?
Screw pump
What accounts for approximately 40% of pump trouble cases for various uses?
Bearing and mechanical seal problems
Which type of gear pump variation includes external, internal, and trochoid pumps?
All of the above
What is the main purpose of a pump onboard a ship?
To continuously transfer a liquid from a low level to a high level with the help of external motive power
Which type of pump locks up a liquid within a certain space and then pushes it out little by little?
Reciprocating pump
What type of pump discharges liquid using centrifugal force generated by the rotation of the impeller?
Centrifugal pump
Which type of pump is designed to transfer any kinds of liquid, such as fresh water, sea water, or oil?
Gear pump
What is the main difference between positive displacement pumps and turbo pumps?
Positive displacement pumps lock up a liquid and push it out little by little, while turbo pumps use centrifugal force to discharge liquid.
What is the classification of onboard pumps based on their working principles and structures?
Non-positive displacement turbo pump and positive displacement pump
Positive displacement pumps continuously transfer a liquid from a low level to a high level using centrifugal force.
False
Volute pumps fall under the category of positive displacement pumps.
False
Mixed flow pumps are a type of turbo pump.
False
Axial flow pumps are a type of positive displacement pump.
False
Friction pumps are categorized as special pumps.
True
The impeller of a reciprocating pump is rotated at a high speed within the casing.
False
Gear pumps are commonly used for transferring gas instead of liquid.
False
Net positive suction head (NPSH) values are independent of pump performance capabilities and suction-side pipe shape.
False
Centrifugal pumps convert potential energy into kinetic energy through high-speed impeller rotation.
False
Multi-stage pumps incorporate upper and lower impellers to pressurize the liquid.
False
Single-suction and double-suction volute pumps draw in the liquid in the same way.
False
Horizontal-shaft and vertical-shaft pumps differ only in the arrangement of their main shaft.
False
Cavitation occurs when a pump operates within its designed suction performance.
False
Pump characteristic curves show changes in net actual head, pump efficiency, and required input power relative to suction values.
False
True or false: Mechanical seal leakage is caused by defective sliding surfaces or damage to O-rings for attaching seal rings?
True
True or false: Overhaul a pump equipped with a flexible coupling and check the shaft center, compare its values with allowable values, and make adjustments if the values exceed the allowable level?
True
True or false: Bearing trouble is usually detected from symptoms such as vibration, abnormal sound, and heating?
True
True or false: Liquid leakage due to poor maintenance of the shaft-sealing device should not be paid sufficient attention?
False
True or false: Open-type ball bearings require periodical replenishment of grease?
True
True or false: The measuring method II for shaft center measuring uses a ruler and a clearance gauge to measure the side surface?
True
True or false: Leakage accounts for almost all mechanical seal problems?
True
True or false: When attaching a mechanical seal, the turning direction of a mechanical seal is not specified?
False
True or false: To attach the rotary part of a mechanical seal, push the seal ring by hand and confirm that it moves freely on the sleeve with a load of the spring?
True
Rotary pumps are not suitable for high-speed operation
False
Discharge amounts in rotary pumps are adjusted by customarily adjusting the flow rate of the main liquid line
False
Gear pumps use two gears of different shapes that rotate in an enclosed casing to carry liquid from the suction side to the discharge side
False
Liquid leakage through the gap between the gears and the casing in gear pumps does not need to be managed
False
Screw pumps generate significant noise and vibration due to continuous and pulsation-free liquid discharge
False
Vane pumps, like balanced vane pumps, do not have grooves for plate-like vanes that rotate while being pushed against the cam ring inner surface
False
Pump ball bearings have an unlimited service life and do not need to be replaced after a prescribed period
False
Study Notes
Rotary Pump Features and Usage
- Rotary pumps push out liquid as the main part rotates and are suitable for high-speed operation.
- Rotary pumps are commonly used for transferring oil and other viscous liquids, as well as in hydraulic systems.
- To start a displacement type rotary pump, it is necessary to keep the bypass line open by opening both the inlet and outlet valves.
- Discharge amounts in rotary pumps are adjusted by customarily adjusting the flow rate of the bypass line.
- Gear pumps use two gears of identical shape that rotate in an enclosed casing to carry liquid from the suction side to the discharge side.
- Gear pumps have variations like external gear pumps, internal gear pumps, and trochoid pumps.
- Liquid leakage through the gap between the gears and the casing in gear pumps must be properly managed.
- Screw pumps are designed to push out liquid by the movement of screw rotors housed in the casing.
- Screw pumps generate minimal noise and vibration due to continuous and pulsation-free liquid discharge.
- Vane pumps, like balanced vane pumps, have a cylindrical rotor with grooves for plate-like vanes that rotate while being pushed against the cam ring inner surface.
- Bearing and mechanical seal problems account for approximately 40% of pump trouble cases for various uses.
- Pump ball bearings have a limited service life and should be replaced after a prescribed period, especially if there is an increase in pump shaft thrust, degradation of lubricant, or increase in pump shaft vibrations.
Rotary Pump Features and Usage
- Rotary pumps push out liquid as the main part rotates and are suitable for high-speed operation.
- Rotary pumps are commonly used for transferring oil and other viscous liquids, as well as in hydraulic systems.
- To start a displacement type rotary pump, it is necessary to keep the bypass line open by opening both the inlet and outlet valves.
- Discharge amounts in rotary pumps are adjusted by customarily adjusting the flow rate of the bypass line.
- Gear pumps use two gears of identical shape that rotate in an enclosed casing to carry liquid from the suction side to the discharge side.
- Gear pumps have variations like external gear pumps, internal gear pumps, and trochoid pumps.
- Liquid leakage through the gap between the gears and the casing in gear pumps must be properly managed.
- Screw pumps are designed to push out liquid by the movement of screw rotors housed in the casing.
- Screw pumps generate minimal noise and vibration due to continuous and pulsation-free liquid discharge.
- Vane pumps, like balanced vane pumps, have a cylindrical rotor with grooves for plate-like vanes that rotate while being pushed against the cam ring inner surface.
- Bearing and mechanical seal problems account for approximately 40% of pump trouble cases for various uses.
- Pump ball bearings have a limited service life and should be replaced after a prescribed period, especially if there is an increase in pump shaft thrust, degradation of lubricant, or increase in pump shaft vibrations.
Learn about the features and usage of rotary pumps, including gear pumps, screw pumps, and vane pumps. Understand how to manage liquid leakage, adjust discharge amounts, and handle common pump trouble cases.
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