Article Index

Low fire start- Used to prove the firing rate of burner controls in the low fire position. To provide safe operating position during light off.

Low gas pressure switch- A control to prevent the burner operation if gas pressure is too low.

Low gas pressure control- A control to prevent the burner operation if gas pressure is too low.

Low oil temperature control- A control to prevent burner operation if the temperature of the oil is too low. (cold oil switch)

Low water cutoff- A safety device used to cut fuel to the boiler when the water level falls below a safe level.

Lug- A bracket applied to boiler suspension, a steel eyepiece fitted and riveted or welded to the curved area of a boiler drum or shell and is connected by a steel U-bolt or sling rod to steel structures overhead.

Make up water- The water added to boiler feed to compensate for that lost through exhaust, blowdown, leakage, etc.

Manhole- The opening in a pressure vessel of sufficient size to permit a man to enter.

Manifold- A pipe or header that collects fluid or distributes fluid to multiple pipes and tubes.

Manual gas shut off valve- A valve in a gas line to be manually turned for completely turning on or shutting off the supply.

Manual reset device- A control that requires resetting by hand to restart the burner once safe operating conditions are restored.

Manufactured gas- Fuel gas manufactured from coal, oil, etc., as differentiated from natural gas.

Maximum allowable working pressure- Is the maximum pressure a pressurized vessel can be exposed to. The MAWP of the completed boiler shall be less than or equal to the lowest design pressure determined for any of its parts.

Maximum continuous load- The period of time the maximum load which can be maintained.

Maximum instantaneous demand- Is a sudden peak load demand and is usually for a short period of time.

Mechanical atomizing oil burner- A burner for firing oil that uses mechanical pressure for atomization in which fuel oil flow is broken down into tiny particles (spray).

Mechanical draft- A forced created by mechanical means.

Micron- A micron is a unit of length equivalent to a millionth of a meter, or 0.000039 in. or 1/25400 in. The diameter of dust particles is often expressed in microns.

MMBtu- Millions of Btus (British Thermal Units).

Moisture- Refers to the presence of a liquid, especially water, often in trace amounts, water in the liquid or vapor phase.

Moisture in steam- Is the amount of water particles carried by the steam, expressed as a percentage by weight.

Moisture loss- The difference in heat content between the moisture in the boiler exit gases and that of moisture at ambient air temperature.

Mud- Particles, precipitates and general impurities that builds up in the lower parts of a boiler. Mud reduces water circulation and so a local buildup may lead to localized overheating.

Mud drum- A water drum, particularly one mounted low on the boiler whose function is primarily to trap mud from circulation.

Mudhole- A small hole near the bottom, through which the sediment is withdrawn.

Multifuel burner- A burner that can use multiply fuels.

Natural circulation- Is the ability of a fluid in a system to circulate continuously, with the difference in density being the only driving force.

Natural gas- Gaseous fuel occurring in nature.