Line D Permissives, Limits, & Interlocks

Question 1

Modern burner controls do not need to be continuously powered.

Answer 1

FALSE

Question 2

What initiates the burner cycle?

Answer 2

The Control Circuit switches being completed

Question 3

List some of the typical switches that could be found on the limit circuit of a boiler.

Answer 3

Manual switch, operating Aquastat, high limit Aquastat, low water cut-off, thermostat, DDC contacts, Pressuretrol, flow switch, aux-low water cut-off.

Question 4

What is the purpose of an interlock?

Answer 4

To stop the burner from firing to prevent an appliance from damaging itself if a condition fails to be satisfied.

Question 5

What must be done when a non-recycling interlock opens?

Answer 5

It must be reset manually

Question 6

What feature shall be included on a low water cut-off that is an interlock for a water boiler that is located above the hot-water circulating system?

Answer 6

It must have a manual reset feature.

Question 7

Define Permissive:

Answer 7

Conditions that need to be satisfied before you can start the equipment cycle.

Question 8

Define Interlock:

Answer 8

Prevents an appliance from damaging itself if a condition fails to be satisfied.

Question 9

List the common run interlocks:

Answer 9

Combustion Air Proving Switch (CAPS), Mag Starter Aux Switch, Low gas Pressure Switch (LGPS), High Gas Pressure Switch (HGPS), Oil Temp Switch, Low Oil Pressure Switch, Low Atomizing Media Switch

Question 10

What type of interlock is required when combustion air is supplied by mechanical means?

Answer 10

A combustion air proving switch

Question 11

What is the “normal” position of a combustion air proving switch?

Answer 11

Open (NO)

Question 12

What is the purpose of the purge interlock:

Answer 12

To prove adequate air supply before the start of the pre-purge countdown timer and during the purge period.

Question 13

How many air changes of the combustion zone and flue passages must take place during the pre-purge period prior to the ignition cycle?

Answer 13

4

Question 14

When shall a proven low fire start be required?

Answer 14

On a variable input appliance that has an input in excess of 1,000,000 BTUH, unless otherwise approved.

Question 15

List 4 types of pre-ignition interlocks:

Answer 15

Start interlock, fuel valve switch, proof of closure switch, overtravel proof of closure switch

Question 16

Define proof of closure switch:

Answer 16

A factory sealed switch incorporated into a safety shut-off valve that includes at least one set of contacts, which close only after the valve port is closed and which open prior to the opening of the valve port.

Question 17

What type of switch is pictured below?

Answer 17

Over Travel Proof of Closure Switch

Question 18

What is the purpose of a low fire start interlock?

Answer 18

To prove combustion air damper and fuel valve are in low fire position before ignition.