ICAR AIEEA-PG — Agricultural Engineering & Technology (Major Subject Group 10) · India · National Testing Agency for ICAR
Original practice questions written to the published syllabus · not past papersOil hydraulics on tractors and machines: pumps, motors, cylinders, valves and circuits.
In the exams: NCEES PE Machinery Systems (hydraulic components and circuits, explicit); elective in the ICAR 6th Deans' Committee B.Tech
ICAR AIEEA-PG and AICE-JRF/SRF (Farm Machinery and Power)
Recall of pump, valve and control-system types and of linkage control modes; at PhD level, load-sensing principles, hydrostatic transmissions, electro-hydraulic hitch control and design trade-offs.
How our questions for ICAR AIEEA-PG spread across the units of Hydraulic Drives & Controls. Difficulty: 32 easy, 51 medium, 11 hard.
| Hydraulic pumps: gear, vane and piston | 13 | |
| Hydraulic cylinders | 13 | |
| Pressure relief and flow control valves | 13 | |
| Tractor hydraulic systems | 12 | |
| Principles of fluid power | 10 | |
| Hydraulic motors | 10 | |
| Pressure drop and heat generation | 9 | |
| Directional control valves | 7 | |
| Open-centre, closed-centre and load-sensing circuits | 7 |
Choose an answer, then open the working. Each explanation says why the right answer is right and why the others are not.
A log splitter uses a 100 mm bore, 70 mm rod cylinder at 200 bar. When the cylinder extends in regenerative mode, the maximum force available is
C. 77.0 kN
Pressure acts on both sides of the piston, so the net area is the rod area: F = 200 × 10⁵ × π(0.07)²/4 = 77.0 kN. The full piston area gives 157.1 kN, available only in normal extension; the annulus gives 80.1 kN, the retraction force; adding the areas has no basis. This is why regenerative circuits switch to normal extension when the wedge meets the log. Adding the areas gives 234.0 kN.
Further reading: Esposito, Fluid Power with Applications
A cylinder must exert 50 kN on extension with a supply pressure of 140 bar, ignoring friction and back pressure. The minimum bore is about
C. 67.4 mm
A = F/p = 50000/(140 × 10⁵) = 3.571 × 10⁻³ m²; D = √(4A/π) = 67.4 mm. √(A/π) is the radius (33.7 mm); 3.57 is the area in a wrong unit; 213 mm comes from treating 140 bar as 14 bar. In practice the next larger standard bore and a friction allowance are chosen.
Further reading: Esposito, Fluid Power with Applications
The lift cylinder that raises a tractor's rear three-point linkage is normally single-acting. This means that
A. oil pressure raises the linkage and the implement lowers under its own weight
A single-acting cylinder is powered in one direction only; on the lift it raises the linkage and the implement lowers by gravity, with a drop-rate valve controlling the speed. A double-acting cylinder has power both ways. Hitch categories concern pin sizes, and no tractor lift uses a spring to raise the load.
Further reading: Goering et al., Off-Road Vehicle Engineering Principles
The cushions built into the ends of many hydraulic cylinders are intended to
A. slow the piston near the end of stroke by restricting the outgoing oil
A cushion spear or collar enters a pocket near the end cap, forcing the exhaust oil through a small adjustable orifice so the piston decelerates instead of striking the cap. It does not add force, lock the piston or filter the oil.
Further reading: Esposito, Fluid Power with Applications
Compared with a direct-acting relief valve of the same size, a pilot-operated relief valve
D. has smaller pressure override and can be vented to unload the pump
A small pilot sets the pressure and controls a main poppet held by a light spring, so pressure changes little with flow, and connecting the vent port to tank unloads the pump. Direct-acting valves respond faster but override more. Pilot-operated valves are adjustable and suit large flows.
Further reading: Esposito, Fluid Power with Applications
A sequence valve differs from a simple relief valve in that the sequence valve
D. has a pressurised working outlet, so it must be drained externally
Both are normally closed and opened by inlet pressure, but a relief valve's outlet goes to tank while a sequence valve's outlet is a working line at pressure, so its spring chamber must be drained externally. Normally open with outlet sensing describes a reducing valve; external pilot opening describes an unloading valve.
Further reading: Esposito, Fluid Power with Applications
A circuit uses an accumulator and a fixed pump. When the accumulator is charged to its set pressure, an external pilot signal from the accumulator line opens a valve that returns pump flow to tank at low pressure. That valve is
A. an unloading valve
An unloading valve is normally closed and opened by an external pilot signal, letting the pump idle at low pressure while a check valve keeps the accumulator charged. Sequence and counterbalance valves are opened by their own inlet pressure, and a reducing valve is normally open and senses its outlet.
Further reading: Esposito, Fluid Power with Applications
Which of the following is the main reason open-centre systems remain common on small and medium tractors?
C. They are simple and cheap, and gear pumps tolerate contaminated oil well
A fixed gear pump with open-centre valves is the lowest-cost system and the most forgiving of dirt. Load sensing is usually more efficient at part load, open-centre functions do interact when operated together, and instant full pressure is a feature of closed-centre constant-pressure systems.
Further reading: Goering et al., Off-Road Vehicle Engineering Principles
In the design of a stationary industrial hydraulic power unit, a commonly used rule of thumb for an open-loop reservoir is a volume of about
D. two to three times the pump flow per minute
Fluid-power texts commonly suggest a reservoir of about two to three times the pump's flow per minute for industrial units, giving time for air release, settling and cooling. Mobile machines use much smaller tanks and rely on coolers. The largest cylinder's volume sets only the minimum working reserve, not the tank size.
Further reading: Esposito, Fluid Power with Applications
On a tractor three-point linkage, the speed at which the implement descends when the lowering command is given is limited by
B. a drop-rate valve that throttles oil leaving the lift cylinder
The lift cylinder is single-acting, so the implement falls by gravity as oil leaves the cylinder; a drop-rate valve throttles that oil to set lowering speed. The relief valve limits maximum pressure, the pump does not push the linkage down, and top-link length sets implement pitch.
Further reading: Goering et al., Off-Road Vehicle Engineering Principles
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