Lab Evaluation

What is low fire on the s’toon boiler?

9-12 psi

What is high fire on the s’toon boiler?

6-9 psi

when does high fire kick in on s’toon boiler?

If low fire isn’t sufficient and drops from 12 psi to 6 psi, the high fire kicks in until 9 psi

What happens after high fire on the s’toon boiler and once pressure is at 9 psi?

Low fire kicks in

How do you change the operating pressures on both high fire and low fire?

use a flat head screwdriver to adjust the screw on top and that changes operating pressures

3M Operating limit

Interlock. On right (west) side of boiler. Initial protection against overpressure and pressure explosion. Trips the fuel safety shut off valves to boiler when pressure gets to 157 psi. Automatic restart is allowed if pressure falls back to operating range of 147 psi. Only interlock that doesn’t require manual reset. Trip value is 157 psi

How do you test the 3m operating limit?

Fire boiler to the trip value of pressure

High limit steam pressure 2M

Interlock. Right (west) side of boiler. Secondary protection against overpressure and pressure explosion. Trips boiler fuel safety shut off valves when boiler pressure reaches 164 psi. Trip value is 164 psi

How do you test the 2M high limit steam pressure?

Bypass the High boiler pressure switch and fire boiler to 164 pressure.

Primary low water fuel cutout

Interlock. Mounted behind water column. there are 4 probes. 1 high, 1 neutral, 1 low, and 1 low low. Probes rely on salt content to generate current to prove safe water level in boiler. Low water condition opens the circuit between the probes. Prevents destruction of boiler tubes and pressure explosion. Trips the fuel safety shut off valves. Trip value is approximately 1” in gauge glass.

How do you test the primary low water fuel cutout?

Fire the boiler with the incoming feedwater valve closed to produce low water condition until boiler trips.

Auxiliary low water fuel cut out

Interlock. To the right of the water column. Float in chamber moves relative to water level. Low level causes open switch circuit to trip the fuel safety shut off valves. Prevents destruction of boiler tubes and pressure explosion. Trip value is 1” in gauge glass

How do you test the auxiliary low water fuel cutout?

Blow down the float chamber while firing boiler

Flame scanner

Interlock. Black box on front of boiler. Uses Ultra Violet light to detect flame presence. Shuts the fuel safety shut off valves if flame is not present during PTFI or normal firing. Prevents furnace explosion from fuel contact with hot surfaces by stopping fuel flow. Trips on lack of flame presence.

How do you test the flame scanner?

Either close the main burner gas valve or pilot gas valve, or keep pilot closed when starting the boiler

Loss of negative air flow

Interlock. Silver box located near force draft fan inlet ducting via tubing connection to pressure switch. Pressure at inlet of fan is negative when fan is on. Loss of negative pressure equates to fan loss and possible furnace explosion due to rich fuel mixture in furnace. Trips fuel safety shut off valves. Trip value is 3 inches water column.

How do you test negative airflow switch.

Disconnect tubing between switch and fan inlet duct while firing boiler.

Loss of outside air

Interlock. Dampers on north wall by top of mezzanine. Outside air comes in to replace air used by the boiler for combustion. Trips the fuel safety shut off valves only if dampers close during operation but also prevents start up if dampers do not open. Damper motor has an internal switch that is made when open, and open when closed.

How do you test the loss of outside air?

Switch the drive motor to closed position while boiler is firing.