Pumps & Heat Exchangers Flashcards
List EIGHT reasons why a bilge pump may not be able to remove water from and engine room bilge
- Filter or Strainer Fouled
- Blocked Strum Box
- Pump/Motor issues such as Single Phasing
- Negative Suction Pressure Head
- Non-Return Valve Stuck or Damaged
- Stator Worn
- Line Damage
- Worn out Wear Rings or Impeller Clearance Issues
- Fluid too Viscus
- Not Enough Fluid to Pump
State the purpose of fitting a bilge injection system on board ship
In extreme cases of engine room flooding, the bilge injection system serves as a last resort to discharge large volumes of water directly overboard.
Describe with the aid of a sketch, the Bilge Injection System
INCLUDES SKETCH
- This valve is only used in EMERGENCIES.
- The Bilge injection valve is always a Screw Down Non-return Valve to prevent accidental flooding of ER.
- The Diameter of the pipe is approximately 2 Thirds (2/3) of the diameter of the pipe for the high/low sea chests. (Must Show on Drawing)
Describe with the aid of a sketch, a Plate Type Heat Exchanger
INCLUDES SKETCH
- A plate heat exchanger uses thin corrugated metal plates to let two fluids flow in separate channels, side by side.
- Hot and cold fluids flow through these alternate channels, which allows for the heat transfer across the metal plates between the fluids.
- Corrugation increases surface area and allows for turbulent flow, this turbulent flow improves heat transfer and prevents fouling
- Compact design makes it space saving and efficient.
State FOUR Advantages and FOUR Disadvantages of plate type heat exchangers
ADVANTAGES
- Larger Surface Area
- Smaller and ore Compact Than Other Heat Exchangers
- Allows for Turbulent Flow
- Extra Plates can be Added to Increase Capacity
DISADVANTAGES
- Expensive to Manufacture and Repair
- Leaks can be Difficult to Locate
- Easy to Overtighten Which can Cause Damage to Plates
- Higher Pressure Drop
With reference to Centrifugal Pumps , explain why large pumps should be started with the discharge valve closed
Centrifugal pumps can be started with the valve open unlike the positive displacement pump.
With the Valve Closed,
- Starting current is reduced, which means the motor doesn’t start under full load.
- This also allows the motor to overcome the inertia of the pump much easier.
- Prevents motor overload during start up.
With the Valve Open,
- Pump starts under full load, requiring high starting current.
- This can overload the motor leading to damage.
- The motor may struggle to overcome the inertia and load at the same time.
- Risk of water hammer due to sudden fluid movement.
State FOUR possible reasons for failing to achieve suction from a double bottom tank
- Blocked Strum Box
- Pump is not Primed
- Wear Ring Worn Out
- Negative suction Pressure Head
- Strainer or Filter Fouled
