Final answer:
When checking pressure in a refrigeration system to assess refrigerant presence, it's true that a pressure rise after a few minutes can indicate liquid refrigerant or refrigerant in the oil. A hydraulic press, however, would not operate as efficiently with a gas because gases are compressible, reducing the press's effectiveness.
Step-by-step explanation:
True. In the context of refrigeration and HVAC (heating, ventilation, and air conditioning) systems, when you're checking the pressure in a system to determine if there is still refrigerant present, it's valid to wait a few minutes to observe if the system pressure rises. This rise may indicate that refrigerant is present in liquid form or absorbed in the oil. Since refrigerants typically change state in response to pressure and temperature changes, as described by the Combined Gas Law, the refrigerant may take a short while to vaporize and exhibit a measurable increase in pressure if it's initially in a liquid state or dissolved in compressor oil.
A hydraulic press typically relies on an incompressible fluid, such as a liquid, to operate efficiently. Using a gas, which is compressible, would not provide the same efficiency because, as explained in Section 14.3, the gas would compress and warm up when force is applied before transmitting that force uniformly as a liquid would in order to move the press. This principle is also why air needs to be removed from brake lines for car brakes to function effectively.