Thomas & Betts RZ-NA 441-OMS Manifold Arrangements, Gas Pressure Switches, Cutoff Control

Figure 20 - Gas Pressure Switches

Low, P/N 93850

(automatic)

High, P/N 93849

(manual reset)

11.Gas Train Including Direct-Fired Burner, Gas Control Systems, and Manifold Arrangements (cont'd)

Service - All Maxitrol Controls: Check all electrical connec- tions. A qualified service person should refer to the Maxitrol Trouble- shooting Guides for assistance in identifying problems and determining the correct solution. None of the Maxitrol controls have field replace- able parts. All components must be replaced with identical replacement parts.

Manifold Arrangements

Description: The manifold is the gas train from the gas supply con- nection to the burner. The manifold selection ordered determines the manifold arrangement including all of the gas train components except the main control valve. Manifold arrangements are available for varying BTUH ranges and gas controls and include versions that meet FM or IRI requirements.

In addition to the Maxitrol valve and two solenoid valves, all manifold arrangements include main gas and pilot gas shut-off cocks, a pilot regulator, and a pilot solenoid valve.

The table below lists the pressure drops through the various types of manifolds by option designation (BM). To determine the required mini- mum supply pressure for natural gas, add 5.0" w.c. to the natural gas manifold pressure drop. For propane gas, add 2.0" w.c.

Figure 19 - Gas Manifold Control Components

Solenoid Valve

Modulating/

Regulating

Valve

Pilot Valve

Pilot Regulator

Manifold Pressure Drops (“ w.c.)

Manifold Opt	BM62			BM63		BM64			BM65		BM67		BM68			BM53		BM66
Manifold Size		1"		3/4"			1"		1-1/4"		1-1/4"			2"		1-1/4"			2"
MBH	Nat		Pro	Nat	Pro	Nat		Pro	Nat	Pro	Nat	Pro	Nat		Pro	Nat	Pro	Nat		Pro
250	.56		.21	.66	.25	.43		.17	.22	.09	.19	.07	.07		.03	.22	.09	.07		.03
500	2.23		.85	2.65	1.01	1.74		.66	.89	.34	.76	.29	.27		.10	.89	.34	.27		.10
750	5.02		1.91	5.96	2.27	3.91		1.49	2.01	.77	1.71	.65	.61		.23	2.01	.77	.61		.23
1000	--		--	--	--	6.95		2.65	3.58	1.36	3.04	1.16	1.09		.41	3.58	1.36	1.09		.41
1250	--		--	--	--	--		--	5.59	2.13	4.76	1.81	1.70		.65	5.59	2.13	1.70		.65
1500	--		--	--	--	--		--	8.05	3.07	6.85	2.61	2.44		.93	8.05	3.07	2.44		.93
1750	--		--	--	--	--		--	10.96	4.17	9.32	3.55	3.33		1.27	10.96	4.17	3.33		1.27
2000	--		--	--	--	--		--	14.31	5.45	12.18	4.64	4.34		1.66	14.31	5.45	4.34		1.66
2250	--		--	--	--	--		--	18.11	6.90	15.41	5.87	5.50		2.09	18.11	6.90	5.50		2.09
2500	--		--	--	--	--		--	22.36	8.52	19.02	7.25	6.79		2.59	22.36	8.52	6.79		2.59
2750	--		--	--	--	--		--	--	--	--	--	8.21		3.13	--	--	8.21		3.13
3000	--		--	--	--	--		--	--	--	--	--	9.77		3.72	--	--	9.77		3.72

Gas Pressure Switches

If the gas train includes either or both high and low gas pressure switches, the switches monitor gas pressure downstream from the safety valves.

If the gas pressure in a system equipped with a high gas pressure switch (Op- tion BP2) exceeds the setpoint, the switch will open the electrical circuit to the burner, stopping all gas flow. The high gas pressure switch is a manu- ally reset device.

A low gas pressure switch (Option BP3) will shutoff the gas flow if the gas pressure drops below the setpoint of the low pressure switch. The low gas pressure switch will automatically reset when the gas pressure rises above the setpoint.

(NOTE: Both high and low gas pres-

sure switches incorporate a vent limiting device and do not require venting to the outdoors when used in an application installed indoors.)

12.Outside Air Cutoff Control (Option BN2; required on C.G.A.-certified units)

Location: The control is in the electrical
	Figure 21 -
box (See Figure 7.); the sensor is in the air
inlet.	Outside Air
Function: After sensing pilot flame, the	Cutoff Control
burner ignites at its lowest input rate. The
"amount of heat" required to reach the de-
sired discharge temperature also depends on
the temperature of the incoming outside air.
The outside air control is factory set at 60°F
(adjustable 25-250°F). The burner reacts
differently depending on the entering air tem-
perature and the setting on the outside air
control. The burner --
• may not ignite (pilot valve will not open);

If the actual temperature of the outside

air is above the setpoint on the outside air control, the burner will not ignite.

•may modulate to satisfy discharge setting;

•may shutdown; or

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