AMT 226 Aircraft Hydraulics Vocabulary

Vocabulary terms and definitions compiled from AMT 226 study questions covering hydraulic fluids, lines, filters, seals, reservoirs, and pumps.

MIL-H-5606

A petroleum base hydraulic fluid that is red in color, will burn, and uses synthetic rubber seals.

MIL-H-8446 (Skydrol 500 A & B)

A phosphate ester base hydraulic fluid that is light purple in color, fire resistant, uses butyl rubber seals, and is adversely affected by water in the atmosphere.

MIL-H-7644 (Old)

A vegetable base hydraulic fluid that is blue in color, will burn, and uses natural rubber seals.

Buna-N

A type of seal material used with petroleum base hydraulic fluids.

Butyl rubber

A seal material used with phosphate ester base hydraulic fluids.

Viscosity

The internal resistance to flow of a liquid.

Filter By-Pass

A component in a filter that prevents the system from becoming inoperative should the filter element become clogged.

Standpipe

A pipe located within a hydraulic reservoir that supplies fluid to the normal supply power pump, leaving fluid below its level reserved for emergency pump operation.

ATA Code 29

The ATA system code corresponding to Hydraulics.

ATA Code 12

The ATA system code corresponding to Servicing.

Double-action pump

A hydraulic pump that delivers fluid with the movement of the pump handle in both directions.

Single-action hydraulic actuating cylinder

A linear actuating cylinder that uses hydraulic fluid under pressure to move the piston in only one direction, with return movement powered by a spring.

Unloading valve

A pressure regulator valve that controls system pressure by shifting the pump outlet fluid back into the reservoir when system pressure reaches the kick-out threshold.

Constant-displacement hydraulic pump

A hydraulic pump that delivers a uniform rate (volume) of fluid flow.

Backup Ring

An additional seal component often necessary when O-ring seals are used in high-pressure systems.

Pump drive coupling shear section

A mechanical safety device located between the driving unit (gearbox) and the pump drive shaft designed to break if the pump seizes to protect it from overload.

Chatter

An operational symptom or sound in a hydraulic pump or system caused by air entering the system.

Pop-out differential pressure indicator

A visual device incorporated into many hydraulic filters to indicate a blocked or clogged filter element.