South Carolina - Packaged Equipment

A single screw compressor uses one main rotor meshing with two star-shaped rotors driven by the main rotor, while basic operating principles are the same as other screw compressors.

A Type B-W gas vent shall terminate not less than 12 feet in vertical height above the bottom of the wall furnace, whereas Type B or L gas vents must terminate not less than 5 feet above the highest connected appliance draft hood or flue collar.

A heat loss HTM is the component U-value times (indoor design temp – outdoor design temp), while a heat gain HTM takes that same temperature difference and adjusts it for sun exposure and heat storage (and is generally looked up on a chart).

O energizes the reversing valve for cooling mode and B energizes it for heating mode; a reversing valve that must be energized in cooling lands on O (combined terminals shown as O/B).

The control closes its contacts and starts the blower at a plenum temperature of about 140°F (60°C), and opens its contacts after burner shutdown when the plenum cools to about 90°F (32°C).

A power burner uses a blower to force both primary and secondary air into the burner tube and is required for fuel oil firing, while atmospheric gas burners rely on siphoning/venturi action of gas through an orifice and are used with fuel gas.

A safe selection rule pairs swing checks with gate valves because flow is straight-way, and pairs lift checks with globe and angle valves because the lift check design requires a change in flow direction.

The split or double disc type should be installed with the stem vertical and handwheel up to guard against jamming of the disc spreader mechanism, while the solid wedge type can be installed in any position without danger of disc jamming.

Gate valves and swing check valves with butt welding ends (and flanged gate valves) use 'Dimension A', while steel globe and angle valves with butt welding ends use '2 × A'.

Thermal compensation is not required when operating temperature extremes differ from installation temperature by not more than plus or minus 30 degrees for Type I, versus 25 degrees for Type II.

Pressure lubrication forces oil under pressure to all bearing surfaces so the compressor runs quieter even with greater bearing clearances, because the pressurized oil film cushions the bearings; a splash system has no pressurized oil cushion.

For listed appliances with draft hoods (and appliances listed for Type B vents) penetrating a combustible wall with single-wall pipe, the ventilated thimble must be not less than 4 inches larger in diameter, reduced to not less than 2 inches larger only where there is a run of not less than 6 feet of pipe in the open between the draft hood outlet and the thimble (6 inches for unlisted appliances with draft hoods; 12 inches for residential and low-heat appliances).

Moving cut-in and cut-out equally in opposite directions keeps the average temperature unchanged; widening the differential (e.g., 26°F/14°F instead of 25°F/15°F) lengthens run time and the interval between cycles, while narrowing it produces shorter, more frequent cycles.

They are equivalent devices that sequence component operation for ignition and monitor operation — primary control units are used in oil furnaces and ignition control modules in gas furnaces.