Question 70 CEL01 - Chief Engineer - Limited

The Correct Answer is D 1. **Why option D ("bleed-off circuit") is correct:** A bleed-off circuit (also known as a bypass circuit) is a method used to control the speed of an actuator by diverting (bleeding off) a controlled amount of hydraulic fluid flow directly back to the reservoir, *before* it reaches the actuator. A flow control valve placed in this bypass line regulates how much fluid goes to the reservoir versus how much goes to the actuator, thus controlling the actuator's speed. Crucially, because the excess fluid is bypassed to the tank (a low-pressure point), the pump does **not** have to operate against the maximum system pressure set by the relief valve, thus saving energy and resulting in the pump operating below maximum operating pressure. 2. **Why the other options are incorrect:** * **A) bleed-in circuit:** This term is not a standard hydraulic circuit designation for speed control. While "bleed" relates to flow diversion, it doesn't describe a recognized standard control strategy like the options B, C, and D. * **B) metered-out circuit:** In a metered-out circuit, the flow control valve is placed in the return line (exhaust side) of the actuator. This controls the speed by restricting how quickly fluid can exit the cylinder. Since the pump must supply the full required pressure to move the load and overcome the restriction on the return side, the pump usually operates *at* or *near* the maximum relief valve setting to maintain motion, contradicting the condition of operating below maximum pressure. * **C) metered-in circuit:** In a metered-in circuit, the flow control valve is placed in the pressure line (supply side) leading to the actuator. This controls the speed by limiting the flow entering the cylinder. Similar to the metered-out circuit, this method requires the pump to build up pressure equal to the load resistance plus the pressure drop across the restriction, often leading the pump to operate at or near maximum relief pressure if the restriction is significant or the load is heavy. It does not inherently feature the energy-saving characteristic of operating below maximum system pressure that defines the bleed-off method.