Step 1: Understanding the Concept:
This question asks for the typical operating pressure range of a modern tractor's hydraulic system. Tractor hydraulic systems are used to power various functions, including the three-point hitch for lifting implements, power steering, and remote hydraulic outlets for operating machinery. These tasks require high pressure to generate significant force.
Step 2: Detailed Explanation:
1. Tractor hydraulic systems are high-pressure systems designed to generate large forces from relatively small actuators (hydraulic cylinders).
2. The pressure is created by a hydraulic pump, which is typically driven by the tractor's engine.
3. The operating pressure is regulated by a pressure relief valve, which opens to return oil to the reservoir if the pressure exceeds a preset maximum, protecting the system from damage.
4. For modern agricultural tractors, this maximum system pressure is typically set in the range of 150 to 200 kg/cm$^2$ (approximately 15 to 20 MPa, or 2100 to 2800 psi).
5. Let's analyze the options:
- 70 to 80 kg/cm$^2$: This pressure is too low for the main hydraulic functions of a modern tractor.
- 100 to 120 kg/cm$^2$: This might be found in older or smaller utility tractors, but it is on the low side for typical modern systems.
- 150 to 200 kg/cm$^2$: This is the standard, widely accepted operating pressure range for the main hydraulic systems of most agricultural tractors.
- 200 to 250 kg/cm$^2$: This is a very high pressure range, more typical of industrial hydraulic systems (like excavators) rather than standard agricultural tractors.
Step 3: Final Answer:
The typical oil pressure in a tractor's hydraulic pump and system ranges from 150 to 200 kg/cm$^2$. Therefore, option (C) is the correct answer.