EVT Hydraulic Systems & Aerial Apparatus Flashcards

What component in a hydraulic directional control valve determines the direction of fluid flow to a cylinder?

Answer: Spool

The spool within a directional control valve shifts position to route hydraulic fluid to either side of a cylinder, controlling direction of movement.

Which standard governs the annual service testing requirements for aerial fire apparatus in the United States?

Answer: NFPA 1901

NFPA 1901 is the standard for automotive fire apparatus that establishes requirements for aerial device design, construction, and annual service testing.

When replacing hydraulic hoses on an aerial apparatus, what minimum burst pressure ratio to working pressure is typically required?

Answer: 4:1

Hydraulic hoses for aerial apparatus are required to have a minimum 4:1 burst-to-working pressure safety factor ratio per industry standards.

What is the purpose of a flow divider valve in an aerial apparatus hydraulic system?

Answer: Distribute equal flow to multiple cylinders simultaneously

A flow divider valve splits hydraulic flow equally between two or more circuits so multiple cylinders extend or retract at the same rate.

What EVT inspection finding would require immediate removal of an aerial apparatus from service?

Answer: Cracks in the aerial ladder main beam welds

Cracks in the aerial ladder main beam welds represent a critical structural failure that requires immediate removal from service until repaired and recertified.

Which type of seal material is most compatible with petroleum-based hydraulic fluids used in aerial apparatus?

Answer: Nitrile (Buna-N)

Nitrile (Buna-N) rubber seals provide excellent compatibility and resistance to swelling when used with petroleum-based hydraulic fluids.