The amount of pressure at which a machine should operate will vary with the job.

The blowing machine should be equipped with a properly operating pop-off valve so that when the wall section is filled, pressure will bleed off at the machine rather than into the sidewall section, eliminating the danger of blowing out the inside wall surface.

Considerably less pressure should be used on a sidewall in which the inner surface is a drywall construction than on one in which the inner surface is lath and plaster. As the insulation is being blown into the sidewall, continually move the blowing nozzle from one side to the other so that the entire stud area will be filled.

The experienced operator will be able to judge the approximate length of time it will take to fill any opening. If an opening is filled too quickly, it probably indicates that the insu- lation has hung up on some type of obstruc- tion. When this occurs, it may be possible, by swiveling the nozzle from side to side, to break the jam. A plumb bob dropped from above may also work. In some cases it will be necessary to make another opening below the stoppage. The applicator should remember that any sidewall section which is not prop- erly insulated will be very evident as a cold spot on the inside wall.