AIRSYS quiz

What physical law states that any pressure applied to any part of a confined liquid is transmitted with undiminished intensity to every other part?

Pascal’s Law

In hydromechanics, what mathematical equation defines hydraulic pressure ($P$) in terms of applied force ($F$) and piston surface area ($A$)?

$$P = \frac{F}{A}$$

What is the primary operational distinction between a passive and an active hydraulic system?

A passive hydraulic system contains no pump and only develops pressure when an input force is applied directly to a piston (such as a light aircraft master cylinder), whereas an active hydraulic system utilizes a power-driven pump to continuously circulate fluid against system restrictions.

What laboratory instrument is used to determine hydraulic fluid viscosity by measuring the time required for $60\,\text{mL}$ of fluid at $100\,^{\circ}\text{F}$ to flow through a standard orifice?

Saybolt Viscometer (measuring in Saybolt Universal Seconds, $\text{SUS}$, or Saybolt Furol Seconds, $\text{SFS}$)

What is the difference between the flash point and the fire point of a hydraulic fluid?

The flash point is the temperature at which a liquid emits sufficient vapor to ignite momentarily (flash) when exposed to a flame, whereas the fire point is the temperature at which it produces sufficient vapor to ignite and continue burning.

Which red-dyed, petroleum-based hydraulic fluid standard dates to the 1940s and is designated as highly flammable?

MIL-H-5606 (active standard: MIL-PRF-5606)

Which fire-resistant, synthetic hydrocarbon fluid was developed as a direct replacement for MIL-H-5606 but is restricted by high viscosity below $-40\,^{\circ}\text{F}$?

MIL-H-83282 (active standard: MIL-PRF-83282)

Which category of synthetic hydraulic fluids is dyed purple or green, used extensively in commercial transport jets, and highly susceptible to atmospheric moisture contamination?

Phosphate ester-based fluids (such as Skydrol and HyJet)

What is the primary functional distinction between hydraulic packings and hydraulic gaskets?

Packings are seals used internally on moving or sliding assemblies, whereas gaskets are seals compressed between static, nonmoving fittings and bosses.

Where must a Teflon backup ring (MS28782) be positioned relative to an O-ring in a high-pressure hydraulic installation?

Downstream of the O-ring (on the side away from the applied pressure to prevent extrusion into component clearances)

How are selector valves hydraulically connected to each other in an open-center system versus a closed-center system?

Selector valves are connected in series in an open-center system, whereas they are connected in parallel in a closed-center system.

What internal reservoir components are installed to suppress vortexing and fluid surging, thereby preventing fluid foaming and pump cavitation?

Baffles and fins

In a nonpressurized hydraulic reservoir, what is the design purpose of routing the main engine-driven pump supply through an elevated standpipe?

To reserve a trapped volume of fluid below the standpipe rim exclusively for emergency or auxiliary pump operation in the event of a main system line leak.

What is the operational function of a filter bypass relief valve in an aircraft hydraulic pressure or return module?

It opens when the filter element becomes clogged and differential pressure increases, ensuring uninterrupted fluid flow to critical flight systems at the expense of filtration.

How does an orifice-type check valve (damping valve) function during landing gear operation?

It permits unrestricted fluid flow in one direction to retract the gear rapidly, while forcing return fluid through a calibrated restrictor orifice in the opposite direction to prevent the gear from extending violently.

What type of directional valve automatically routes pressurized fluid from either the normal or alternate/emergency hydraulic supply to an actuator while isolating the inactive line?

Shuttle valve

What component unloads a constant-delivery hydraulic pump by routing its output directly to the reservoir at low pressure once normal system operating pressure is attained?

Automatic Cut-out Valve (ACOV) or pressure regulator

What internal mechanical barrier divides the pressurized hydraulic fluid chamber from the compressed nitrogen gas chamber in a cylindrical accumulator?

A floating piston

Where are transport aircraft hydraulic heat exchangers typically installed, and what fluid acts as the cooling heat sink?

Inside the aircraft fuel tanks, utilizing cold fuel circulating over aluminum finned tubes to absorb heat from the hydraulic fluid.