Load characteristic of gear pump and centrifugal pump used on ship
Gear pump load characteristics with example:
Gear pump is used for transferring heavy fuel oil and its motor current is directly proportional to pump discharge pressure. In a gear pump discharge pressure is the most important factor. If gear pump loses suction slowly the discharge pressure will decrease and if the discharge pressure decreases the current amperage will reduce.
Let’s see few case studies to understand it in a better way. Look at the diagrams to identify when flow is taking place:
Case 1: When the gear pump is not running, the pressure is zero and the amperage is also zero.
Case 2: When the gear pump starts running normally.
Case 3: Now somebody by mistake closes the valve and pressure starts increasing.
Case 4: Pressure increases up to 8 bars by the time valve is fully shut and relief valve lifts:
Now in this case the relief valve has lifted and no more pressure will increase due to which the pipe or the pump casing will not burst.
Centrifugal pump load characteristics with example:
A centrifugal pump is used as sea water pumps. In Gear pump pressure decides motor amperage, but in centrifugal pump it is the flow of fluid through the eye of the impeller that decides motor amperage. In centrifugal pump when it loses suction, the flow rate decreases causing motor amperage to decrease.
Let’s see few case studies to understand it in a better way. Look at the diagrams to identify when flow is taking place:
Case 1: Only No 3 seawater pump is running and one cooler is in used.
Case 2: Only No 3 seawater pump is running and both the coolers are in used.
In this case we can see that the flow has increase but the pressure has decreased still the current amperage has increases because in centrifugal pump only flow matters.
Case 3: Both coolers not in use
In this case both the coolers are not in use so no flow is taking place but the pressure is decreasing but still the current amperage drops to 10amps. This clearly signifies that amperage is dependent in flow and not on pressure for centrifugal pump.
Note:
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