Auxiliary Pneumatic systems Flashcards
(33 cards)
Why are fusible plugs fitted to air compressors?
Fusible plugs are safety features built In air compressors and play a vital role in avoiding overheating and overpressure scenarios.
During operation, air compressors can generate significant heat due to compression. If the cooling system fails, the temperature may rise dangerously. The are designed to help vent the compressed air safely to avoid further failure of the equipment.
Why are fusible plugs fitted to air receivers?
Purpose in an air receiver: Air receivers (storage tanks for compressed air) may encounter dangerous pressure or heat buildup. Fusible plugs are installed to mitigate these risks.
- Prevent explosion: If heat from nearby equipment (like an engine room) increases the temperature of the air in the receiver, pressure rises. The fusible plug melts at a preset temperature, releasing pressure.
- Maintain system integrity: By venting air, fusible plugs prevent structural failure of the air receiver, which could lead to explosions.
- Safety compliance: Fusible plugs ensure compliance with safety regulations and standards in marine and industrial environments.
Label compressor drawing
Explain the emergency operation of a pneumatically operated friction clutch
A pneumatically operated friction clutch relies on compressed air to engage and disengage the clutch mechanism. In an emergency situation, the operation of the clutch must ensure rapid disengagement to prevent damage . Here’s how it typically works:
- Loss of Air Pressure – If the system experiences a sudden drop in air pressure, the clutch may automatically disengage due to spring-loaded mechanisms that push the friction plates apart.
- Emergency Release Valve – Many systems incorporate a manual or automatic emergency release valve that quickly vents air from the actuator, ensuring immediate disengagement.
- Fail-Safe Spring Mechanism – Some designs use a fail-safe spring that forces the clutch to disengage when air pressure is lost, preventing unintended engagement.
- Backup Air Supply – In critical applications, a secondary compressed air source or accumulator may be used to maintain clutch operation temporarily until the main system is restored.
- Manual Override – Certain systems allow for manual disengagement using a mechanical lever or override mechanism in case of pneumatic failure.
With reference to reciprocating air compressors:
(a) state the meaning of the term bump clearance;
(b) explain the effects on operation if the bump clearance is: low and high
(c) explain how an aftercooler helps remove moisture from the air
(a) Meaning of Bump Clearance:
Bump clearance refers to the minimum distance between the piston and the cylinder head when the piston is at top dead center (TDC). This clearance ensures that the piston does not physically collide with the cylinder head during operation.
(b) Effects on Operation if Bump Clearance is:
-
Too Small:
- Risk of Collision causing damage
- Increased Compression Pressure and to higher temps
- Reduced Safety Margin
-
Too Large:
- Reduced Volumetric Efficiency
- Lower Compression Pressure
- Increased Re-expansion Losses
(c) How an Aftercooler Removes Moisture
An aftercooler cools the compressed air, causing water vapor to condense into liquid droplets. These droplets are then removed through a drain system, preventing moisture-related issues such as corrosion and inefficiencies in pneumatic systems
State 3 reasons that may cause a pneumatic relief valve to lift in service (3)
A relief valve may lift in service due to the following reasons:
- Excessive System Pressure If the pressure in the system exceeds the valve’s set point, it will open to release excess pressure and prevent damage.
- Thermal Expansion Temperature changes can cause fluid expansion, increasing pressure beyond safe limits and triggering the relief valve.
- Valve Malfunction or Blockage A faulty valve or obstruction in the system can lead to improper pressure regulation, forcing the relief valve to lift unexpectedly.
State 3 reasons that may cause a relief valve to fail to lift should excessive pressure occur (3)
Here are three reasons a relief valve may fail to lift under excessive pressure:
- Valve Blockage – Debris or contamination in the valve can obstruct its operation, preventing it from opening.
- Incorrect Calibration – If the valve’s set pressure is improperly adjusted, it may not activate at the intended pressure level.
- Spring Failure – A weakened or broken spring can prevent the valve from responding to pressure changes effectively.
explain how the correct operation of a relief valve is ensured (4)
Ensuring the correct operation of a relief valve involves several key practices:
- Regular Maintenance: Periodically inspect and clean the valve to prevent blockages or corrosion that could hinder its function.
- Calibration: Adjust the valve to the correct set pressure using manufacturer guidelines to ensure it activates at the intended pressure level.
- Functional Testing: Perform tests to verify the valve opens and reseats properly under simulated pressure conditions.
- Component Checks: Inspect critical parts like springs, seals, and seats for wear or damage, replacing them as needed.
- Environmental Considerations: Protect the valve from extreme temperatures or corrosive environments that could affect its performance.
With reference to air compressors explain why an air filter is important
- Prevents Contamination: Air filters remove dust, dirt, oil, and other impurities from the intake air, protecting the compressor’s internal components from wear and damage.
- Improves Efficiency: Clean air reduces pressure drops and ensures smooth operation, enhancing the overall efficiency of the compressor.
- Protects End Applications: In industries like painting or food processing, clean compressed air is essential to maintain product quality and prevent equipment malfunction.
Why the compressor should not be allowed to run with a dirty air filter
Running a compressor with a dirty air filter can lead to several issues:
- Reduced Efficiency: A clogged filter restricts airflow, forcing the compressor to work harder and consume more energy.
- Component Damage: Dirt and debris can bypass the filter, causing wear and tear on internal parts like valves and pistons.
- Overheating: Restricted airflow increases operating temperatures, which can lead to overheating and potential system failure.
4.Risk to end user or equipment Contaminated air can carry harmful particles, leading to respiratory issues or allergic reactions, especially in sensitive environments like healthcare or food processing.
depending on the type of aircompress and what it used for.
With reference to air compressors state two advantages of rotatry air compressors (2)
Rotary air compressors offer several advantages over other types. Here are two key benefits:
- Continuous Operation – Unlike piston compressors, rotary air compressors can run continuously without overheating, making them ideal for demanding industrial applications.
- Energy Efficiency – Their design allows for lower energy consumption, reducing operating costs while maintaining high performance.
Would you like to explore more advantages or compare them with other compressor types?
1 advantage of a reciprocating air compressor (1)
One key advantage of a reciprocating air compressor is its ability to generate high-pressure air, making it ideal for applications requiring intense compression.
Explain why multistage air compressors are used for starting air purposes
Multistage air compressors are used for starting air purposes because they provide high-pressure air efficiently while minimizing temperature rise. Here’s why they are preferred:
- Higher Pressure Generation – Multistage compression allows air to be compressed in stages, reaching the required high pressure (often around 30 bar) needed for engine starting.
- Intercooling Between Stages – Cooling the air between compression stages reduces its temperature, improving efficiency and preventing excessive heat buildup.
- Reduced Workload on Each Stage – By dividing compression into multiple stages, each stage operates at a lower compression ratio, reducing mechanical stress and improving reliability.
- Improved Efficiency – Multistage compressors consume less energy compared to single-stage compressors when achieving high pressures.
What is the difference between a bust disc and fusable plug in an air compressor system
A burst disc and a fusible plug are both safety devices used to relieve pressure, but they operate differently:
- Burst Disc: This is a thin diaphragm designed to rupture at a specific pressure threshold. When the pressure inside a system exceeds the set limit, the disc bursts, permanently opening a passage for pressure relief. The setting pressure cannot be adjusted once installed.
- Fusible Plug: Instead of responding to pressure, a fusible plug reacts to temperature. It contains a metal alloy that melts when exposed to excessive heat (typically above 105°C), allowing pressure to escape. Like a burst disc, it cannot be reused once activated.
Label the following diagram for an insturment air system
Draw and label the following filter tower for a breathable air compressor
With reference to a fully automatic water cooled starting air compressor
1. state the alarms that should fitted
2. explain how damage from over pressured is prevented in EACH of the following.
* intercoolers
* water jackets
1. Alarms for a Fully Automatic Water-Cooled Starting Air Compressor
To ensure safe operation, the following alarms should be fitted:
- High Discharge Pressure Alarm – Warns of excessive pressure buildup.
- Low Discharge Pressure Alarm – Alerts if pressure drops below operational limits.
- High Cooling Water Temperature Alarm – Prevents overheating in cooling jackets.
- Low Cooling Water Level Alarm – Ensures adequate cooling water supply.
- Low Starting Air Reservoir Pressure Alarm – Indicates insufficient air pressure for engine starting.
- Compressor Motor Overheat Alarm – Protects against excessive motor temperature.
2. Overpressure Prevention
#### Intercoolers
- Pressure Relief Valve – Opens to release excess compressed air, preventing rupture.
- Bursting Disc (Optional) – Acts as a secondary safety measure, rupturing at a set pressure limit.
Water Jackets
- Temperature Monitoring & Alarms – Detects overheating before pressure becomes critical.
- Pressure Relief Valve and fusable plug – Used in high-pressure applications to release excess pressure.
- list FIVE fittings on the shell of an air receiver
- explain the purpose of the fittings listed in (a)
Five Fittings on the Shell of an Air Receiver
1. Safety Relief Valve – Prevents overpressure by releasing excess air.
2. Pressure Gauge – Monitors internal pressure to ensure safe operation.
3. Drain Valve – Removes accumulated moisture and contaminants.
4. Inspection Opening – Allows internal examination for maintenance and safety checks.
5. Inlet & Outlet Connections – Facilitate air intake and distribution to the system.
Purpose of Each Fitting
- Safety Relief Valve – Protects against excessive pressure buildup, preventing vessel rupture.
- Pressure Gauge – Provides real-time pressure readings to maintain operational limits.
- Drain Valve – Prevents water accumulation, which could lead to corrosion or reduced efficiency.
- Inspection Opening – Enables visual checks and maintenance to ensure structural integrity.
- Inlet & Outlet Connections – Ensure proper airflow for system functionality.
Sketch a block diagram of the layout of a compressed air system for the supply of starting and control air.
With reference to main air recievers
a) list four safety features, stating the purpose of each
b) state the pressure at which the relief valve should lift
a) Safety Features of Main Air Receivers
1. Safety Relief Valve – Prevents overpressure by automatically releasing excess air when the pressure exceeds safe limits.
2. Pressure Gauge – Allows monitoring of internal pressure to ensure safe operation and detect potential issues.
3. Drain Valve – Removes accumulated moisture, preventing internal corrosion and maintaining efficiency.
4. Inspection Openings – Enable regular checks and maintenance to ensure structural integrity.
b) Relief Valve Lift Pressure
The relief valve is typically set to lift at 10% above the maximum working pressure to protect the system from overpressure situations.
With reference to an air supply for pneumatic control system
a) state three contaminants that may be present
b) explain why the contaminants stated in a) are undesirable.
Contaminants in Pneumatic Control Systems
1. Moisture (Water Vapor)
2. Oil Mist
3. Dust & Particles
Why These Contaminants Are Undesirable
- Moisture (Water Vapor) – Causes corrosion, rust, and potential freezing in colder conditions, leading to system failures.
- Oil Mist – Can clog valves, degrade seals, and reduce the efficiency of pneumatic components.
- Dust & Particles – Causes wear on moving parts, obstructs airflow, and reduces system precision.
(a) Explain the circumstances under which EACH of the following devices fitted
To an air compressor may operate:
(i) Fusible plug
(ii) Burst disc
b) state where each device in a) may be fitted
(a) Operation of Safety Devices on an Air Compressor
#### (i) Fusible Plug
- Operates when the compressor reaches dangerously high temperatures.
- Contains a metal alloy that melts at a predetermined temperature, releasing pressure to prevent overheating or explosion.
- Commonly used in steam systems and high-pressure environments.
(ii) Bursting Disc
- Functions as a pressure relief device, designed to rupture when the system pressure exceeds safe limits.
- Provides immediate pressure release to protect equipment from catastrophic failure.
- Used as a backup to safety valves in high-pressure applications.
(b) Locations of Each Device
- Fusible Plug – Typically fitted near heat-sensitive components such as the cylinder head or discharge side of the compressor. or on the water jacket of a water cooled compressor.
- Bursting Disc – Installed on the pressure vessel or air receiver to act as an emergency pressure relief mechanism. or on the intercooler incase of failure.
With reference to starting air receivers, explain EACH of the following:
(a) Why they should be drained regularly
(b) Why outlet valves should be opened slowly
(a) Why Starting Air Receivers Should Be Drained Regularly
- Prevents Water Accumulation – Condensation forms inside the receiver and can lead to excessive moisture buildup.
- Reduces Corrosion Risk – Water can cause rusting of internal components, weakening the structure.
- Maintains Air Quality – Moisture in the air system can affect efficiency and damage connected equipment.
- Avoids Freezing Issues – In colder environments, accumulated water may freeze and obstruct airflow.
- Improves System Performance – Regular draining ensures dry air supply, enhancing reliability.
(b) Why Outlet Valves Should Be Opened Slowly
- Prevents Sudden Pressure Surges – A rapid opening can cause shock waves in the system, potentially damaging components.
- Avoids Overloading the System – A controlled release allows downstream equipment to adjust gradually.
- Reduces Risk of Equipment Damage – Sudden airflow may harm sensitive parts like actuators and filters.
- Enhances Safety – Abrupt pressure changes can pose hazards to personnel working near the system.
- Maintains Stable Air Supply – A gradual opening helps regulate airflow for smooth operation.
Explain why an accumulator is necessary in compressed air systems
An accumulator is essential in compressed air systems because it helps regulate pressure and ensures a steady supply of air. Here’s why it’s necessary:
- Stabilizes Pressure – Absorbs fluctuations in air demand, preventing sudden pressure drops or surges.
- Improves System Efficiency – Reduces strain on compressors by storing excess air for peak usage.
- Enhances Performance – Maintains consistent airflow, ensuring smooth operation of pneumatic tools and equipment.
- Protects Components – Minimizes wear and tear on compressors and valves by reducing frequent cycling.
