Chapter 9 Mechanical Devices Used in Gas Appliances Flashcards
What are the mechanical devices used in gas appliances
orifices gas pressure regulators valves safety and operating control devices thermostats gas piping
What are the 4 broad categories of gas orifices
Fixed orifices
Adjustable orifices
Universal Orifices
Orifices with fixed needles
What are the two main functions of a gas flow control orifice
control the amount of gas being injected into a gas appliance
Draw in or aspirate primary air into the gas burner
Will the NG or LP gas orifice be larger in diameter
The NG orifice will be larger in diameter
what is the primary function of a gas pressure regulator
control the incoming gas pressure of the fuel flowing into the orifices
Must be able to control the gas pressure w/in a relatively narrow pressure range
what do valves do
they are devices that directly control gas flow
what three elements must gas appliance safety and operating control systems incorporate
Sensing device
final control device
actuator that connects the first two
what is flame rectification
safety technique used to “prove flame”
presence of gas flame allows DC current to flow through the flame into control relays
What is an electrical rectifier
device that limits current flow in one direction only
Gas flames possess this capability
Where can flame sensing occur
at the gas burner port or at the burner pilot
what are 6 devices used to sense pilot gas flame
thermocouple sensor bi-metal sensor hydraulic sensor mercury vapor sensor optical sensor flame rectification sensor
what are thermostats
automatic gas control devices
enable an operator to preset a desired temp
four types of thermostats used in the gas appliance industry
electronic
hydraulic
rod and tube
bi-metal
five factors that influence pressure losses in gas piping
gas flow rate gas pipe diameter gas pipe length Local Reynolds number (related to velocity) Inside pipe wall roughness
Pipe length, diameter and gas flow rate most significant
