REGULATORS
PRESSURE TAPS FOR CROSS-CONNECTION IMPULSE LINES
GOOD
BAD
BAD
BEST
do not allow any protrusion into pipe
remove burrs
BEST
5 pipe dia .
3 pipe dia.
It is best to locate impulse tap on top or side of pipe, parallel to valve shaft, with undisturbed straight runs upstream and downstream. BAD ACCEPTABLE
Avoid elbows, tees, sharp edges and abrupt changes of flow direction. Burrs or nipples projecting into the pipe cause the air to speed up. Any change in velocity gives a false pressure reading. The off-center flow downstream of any valve will have less bad influence on an impulse if the tap is parallel to the valve shaft. Tap from the side or top of a pipe to prevent condensate or dirt from entering. Avoid dips or U's in impulse lines - condensed water could collect. Pitch the impulse line so water will run back to the air line - not to the regulator, where weight on the diaphragm could "fool" the regulator. Connect the regulator end of an impulse line last. Blow out the impulse line from the regulator end until air comes through the tapped pipe. Easiest is usually through a threaded connection provided in most burner mounting plates (see page 19), but internal flow of some burners creates a misleading negative pressure in the mounting plate. 4422, 4441, 4442, 4425, 6422, and 6425 burners may have as much as 22.2" wc suction (-8A size at 16 osi air pressure) at the mounting plate, but be positive at the ends of the air tubes, causing as much as 4% error in the air/ fuel ratio. If critical, relocate the chamber pressure tap as follows: Use a tee and large observation port on the end of a tap to permit easy checking for blockage. Locate taps well above a level where hearth scale or splashing liquids might plug them. A pressure tap should not be opposite a burner, or near a flue, or in any other position where velocities are high. A pressure tap should not be directly below a burner, else it could become a flue-way for hot gas circulation between the refractory and furnace shell. TAPS FOR MEASURING CHAMBER (FURNACE) PRESSURE
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