Combustion Catalog | Fives North American

System Design Tips | Gas Pilots


• The preferred location for pilot tips (and UV cells) is on the top or side of a burner so that scale, dirt, and refractory crumbs can- not fall into it. • Most pilot systems will operate more reliably if they use a cross-connected ratio regulator to control the air/fuel ratio. This is done by connecting the regulator vent with an impulse line to the 3065 mixture pressure tap or to the 3065 air pressure tap. Using the mixture pressure tap provides better air/fuel ratio control (especially on suction systems).

• Undersized piping and plugged lines are common causes of pilot problems. Avoid corrugated connectors and hoses, they cause more pressure loss than regular pipe and fittings. Tubing has ½ the area, and 4 times the pressure loss of the same “size” pipe. It’s OK to use tubing that has as much flow area as pipe. (Example: use 7⁄8 "OD × .045"wall tubing in place of ¾ " pipe) • Avoid thread dope or Teflon tape applied over the ends of pipe thread, it can break loose and plug pilot tips.

2 threads

Gas line



3065 Mixer

Pilot tip

Cross connected regulator

• Always BLOW OUT EACH FITTING & SECTION OF pipe before and after installing it, (but don’t put pressure on regulators and solenoid)

Impulse line

Air valve

• While it may be tempting to feed multiple 4025 tips with a single higher capacity mixer, this hurts reliability and is not nor- mally recommended with these larger pilots. • Short run impulse lines for pilot systems can be ¼ " thin wall tubing. 304 stainless tube ¼ " OD x .035" wall is a good choice. Copper tubing can also be used, but is more susceptible to kink- ing. For longer impulse line runs (over 24") consider using 3⁄8 " O.D. thin wall tubing. • If the pilot regulator inlet gas pressure exceeds its pressure rat- ing, install a pressure-reducing regulator upstream. 7344 Regula- tors reduce up to 25 psi gas to 4-12"w.c. For capacities or inlet pressures beyond the range of 7344 Regulators, see Bulletins 7337 and 7349. Use a separate pilot regulator. Do not run pilot gas through any of the regulators for main burner gas because those regulators cannot turn down low enough for pilot gas flow, and will therefore chatter or shut-off. • The inlet pressure to the pilot gas ratio regulator (7218) should be at least 2 osi greater than the connected pilot air or mixture pressure. • Avoid stressing and distorting valves and regulators, small pilot regulators may be easily damaged by incorrect use of wrenches. Put your wrench on the end nearest the pipe that it’s being threaded into.

compressed air


• A filter on the combustion air blower inlet will help prevent plugging the small openings in the pilot system with dirt and debris.

• The R240-2465 igniter may light the pilot better if the ground electrode is bent 45° resulting in a 0.09"-0.10" gap.

The 4-7051-1 spark plug is a R240-2465 igniter with a pre-bent ground rod to provide the larger gap.

• Avoid running ignition cables or control wiring close to flame supervision cables. The signal traveling through flame rod cables are very susceptible to interference from other electrical wiring. • If a longer pilot flame is needed, consider a 4014 gas boosted pilot tip assembly. For a smaller pilot tips consider the 4011/4021 pilot set/pilot. • For additional pilot system information see guides in these bul- letins and sheets. 3065, 4000-3, 4085, 4065, 4011/4021, 4014, 8800-1, 8800-2.



Bulletin 4015/4025 Page 6

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