A counterbalance valve is normally a _______ valve:

A counterbalance valve is designed to maintain a predetermined pressure in a hydraulic system, particularly to control the movement of a load and ensure stability during operation. The valve utilizes a double-poppet design to achieve this functionality.

The double-poppet configuration allows the valve to respond dynamically to changes in load conditions. When the load attempts to descend, one poppet opens to allow fluid flow back to the reservoir, while the other poppet remains closed until the system pressure reaches a predetermined level. This ensures that the load is held in place and does not descend uncontrollably, providing safety and operational reliability.

In contrast, single-acting valves typically allow flow in one direction only and do not provide the same level of control over load movement. Variable valves can adjust flow rates but do not inherently provide the counterbalance function. Throttle valves primarily restrict flow and do not possess the specialized function of load stabilization. Hence, the double-poppet configuration is crucial for the operation of a counterbalance valve, making it the correct choice in this context.