Basic Water Heating Systems Flashcards
Wgat is the max capacity of a class 2 transformer?
100 VA
What is the purpose of the reverse acting aQuastat?
It prevents cold water from circulating through the system.
What is the name of a device that transfers heat from one system to another?
Heat exchanger
The main burner on a hot water heating boiler may be inited with
A standing pilot flame
Direct spark ignition (DSI)
Hot Surface Ignition (HSI)
How does a standing pilot flame work?
Has a pilot flame the burns constantly
Is in direct contact with the thermocouple, near the main burner.
Not allowed for new applications , may encounter then in old ones
These transformer are typically 10kv and are a significant shock hazard.
How does a dsi work
Uses a high voltage source to create a hot spark across a spark plug.
When main gas valve opens it calls for a spark. Ignition transformer energizes and causes continuous spark until flame proving device senses a flame and opens ignition circuit
Describe an hsi?
Resistive ignition similar to toaster.
Current flows through resistive element when ignition is required.
Element de-energizes when main flame proving exists.
Does not require a high voltage.
What is a thermocouple? How does it work?
Flame proving device.
It is heated by a pilot flame.
Energizes automatic pilot valve
Pilot valve opens
Opens gas lines to main gas valve and burner.
Both valves shut off in loss of pilot flame.
Electronic flame proving device?
Uses a dc generator, an ignitions and a spark plug to supply a spark to ignite the main gas.
Flame rod detects if flame is present, acts as a conductor and completes the flame provin interlock circuit.
Flame rods have fast response time
What is a pyrostat?
A flame proving device
Also called a stack switch
A bimetal coil incorporated into a probe.
Probe senses heat, after a time delay, locks out the safety switch to provide shutdown protection.
What is a cad cell?
Flame proving device.
Light sensitive
Mounted so the the flame strikes it directly.
High resistance in no light.
When it sees flame resistance drips between 300 and 1000 ohms and allows current to flow.
What is a zone valve?
A 24V hot water valve supplied by a class 2 transformer and controlled by a 24 V t-stat.
What can an end of travel switch be used for?
To permit the sequencing of auxillary equipment.
When a valve opens fully, its end of travel switch contacts close and start the circulating pump and the boiler burner
What is a lwco and what does it do?
A low water cut out shuts off the fuel supply to the burner if the water boiler falls below acceptable levels.
Sever damage can occur to the boiler if it fires without an adequate water supply.
What is the most common lwco?
Float operated device.
