Question 41 3AE02 - Third Assistant Engineer (Alt)

The Correct Answer is B. ### Why Option B ("floating ring and cylinder body") is Correct In a variable displacement radial piston pump (specifically, the type where displacement is varied by changing the eccentricity), the **direction of flow** and the **fluid flow rate** are directly determined by the relative geometric positions of the **floating ring (or reaction ring/casing)** and the **cylinder body (or rotor assembly)**. 1. **Fluid Flow Rate (Displacement):** The pump's displacement (and thus flow rate for a given speed) is proportional to the eccentricity ($e$), which is the distance the cylinder body's rotation center is offset from the floating ring's inner surface center. By moving the floating ring laterally relative to the stationary central axis of the cylinder body, the stroke of the pistons is changed, thereby varying the displacement and flow rate. 2. **Direction of Flow (Reversibility):** If the floating ring is positioned to one side of the cylinder body's center, the volume on one side of the rotation (suction) is greater than the volume on the other (discharge), establishing a flow direction. If the floating ring is moved across the center point to the opposite side (changing the sign of the eccentricity), the roles of the suction and discharge ports are reversed, thereby reversing the direction of the fluid flow out of the pump. Therefore, the relative position between these two main components dictates both the rate and the direction of the output flow. ### Why Other Options Are Incorrect **A) floating ring and pump shaft:** While the floating ring and pump shaft are key components, the **pump shaft** (which is fixed in position relative to the cylinder body center) determines the rotational speed, but the **relative** position of the floating ring to the **cylinder body** (the rotating component containing the pistons) determines the actual stroke and eccentricity, which dictates flow rate and direction. The direct determinant is the relationship between the ring and the pistons/cylinder body, not the ring and the shaft itself. **C) pump shaft and horizontal ports:** The **pump shaft** provides the rotational energy. The **horizontal ports** (suction and discharge) are fixed features that direct the fluid in and out. The relative position between the shaft and the ports does not change and therefore cannot determine the variability of the flow rate or the flow direction. **D) pump shaft and central valve:** The **pump shaft** provides rotation. The **central valve (or pintle)** is a stationary component that directs the fluid to and from the correct port depending on the piston's position (inward or outward stroke). While crucial for operation, its position relative to the shaft is fixed and cannot be adjusted to change the flow rate or reverse the flow direction.