Limit Controls & Thermostats Flashcards
What is a heat anticipator and it’s purpose?
A small electrical resistance heater that fools the thermostat into thinking it is warmer then it actually is.
What is a limit control?
Temperature or pressure actuated switch. Generally to groups low and high limit switches. Either direct or reverse acting.
What direct and reverse acting men?
- Direct acting controls break(open) on temp rise
- Reverse acting controls make(close) their contacts on temperature rise.
Open meens no electrical current closed means electrical current.
What is a high limit control?
Safety device that cuts off power to oil burner only if temp or pressure gets to high. Should not cut off circulator or fans do to they get rid of excessive heat. Wired in series with primary.
What is a combination can and limit switch used for?
Protect Furnace heat exchange from high temps.usually combined in one housing.
What are steam pressure controls?
(Pressuretrols) limit controls that respond to changes in steam pressure.Should not exceed 15 PSI.
Residential steam is 2 PSI or less.
How are pressure control set for steam?
They are either subtractive or additive.
Example:
Cut out is set at 3 PSI and the differential is set at 2 PSI the cut in point is 1 PSI(subtractive)
Cut in point is 1 PSI and differential is set at 2 PSI the cutout is 3 PSI
Additive
Where and how should steam pressure controls be installed?
Above the water level with a pigtail/siphon and level.
What is a low water cutoff?
Prevents Boiler operation if water level is to low.Required in all steam boilers. Installed on other boilers if system is above or at same level of radiation.protects Boiler in loss of water.
