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Difficulty: HardProperties of Fluids

A heavy-duty hydraulic press is designed to operate using hydraulic oil with a specific gravity of 0.85. During maintenance, a large volume of air is accidentally trapped in the sealed main pressure line. When the pump applies 2,000 psi of pressure to the system, which of the following best describes how the properties of the contents will affect the machine's operation?

  1. The trapped air will compress significantly before the oil can transmit full force, causing a delayed and spongy cylinder response.Answer
  2. B
    The oil and the trapped air will compress equally, generating standard force but causing the cylinder to actuate at a much faster speed.
  3. C
    The oil will compress into a smaller volume due to its specific gravity being less than 1.0, while the air will resist compression and block fluid flow.
  4. D
    The trapped air will maintain a constant volume but increase in density, acting as a solid barrier that prevents the hydraulic oil from transmitting any pressure.

Answer

The trapped air will compress significantly before the oil can transmit full force, causing a delayed and spongy cylinder response.
Hydraulic systems rely on the incompressibility of liquids to transmit force instantaneously and efficiently. When air (a gas) enters the system, it acts like a weak mechanical spring because gases are highly compressible. The pump's applied pressure will first crush the air pocket into a smaller volume before enough pressure builds up to move the heavy cylinder, resulting in a delayed, inefficient, and spongy mechanical action.

Step-by-Step Solution

1
Identify the two different fluids in the closed hydraulic system.
The system contains a liquid (hydraulic oil) and a gas (air).
Different phases of matter respond completely differently to applied pressure.
2
Evaluate the compressibility of each fluid.
Liquids are nearly incompressible, meaning their volume remains virtually constant under high pressure. Gases are highly compressible, meaning their volume decreases significantly when pressure is applied.
Understanding compressibility is essential to predicting the physical behavior of the system.
3
Determine the mechanical effect on the hydraulic press.
When the 2,000 psi is applied, the work energy initially goes into compressing the trapped air pocket rather than moving the cylinder. This creates a delay and a soft, 'spongy' feel until the air is fully compressed.
Force cannot be efficiently transmitted through a fluid medium until all highly compressible elements in the line are reduced in volume.

Key Concept

Fluid Compressibility
Estimated Time:1m 0s
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Topics

Properties of Fluids

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