Thomas & Betts UDAS, UDAP Gas Piping and Pressures cont’d, Single-StageValve, Two -StageValve

12.Gas Piping and Pressures (cont’d)

Derate by Valve Outlet Pressure Adjustment for High Altitude Operation

This adjustment can only be done after the heater is in operation. It is included in the startup procedures.

NOTE: If elevation is above 6000 ft (1830M), a high altitude pressure switch is required; see Paragraph 7.

FIGURE 11 - Top View of Valves showing Outlet Pressure Tap and Adjustment Locations

Single-Stage Valve

Output

Instructions for High Altitude Derate

1.Determine the required valve outlet pressure for the elevation where the heater will be operating. If unsure of the elevation, contact the local gas supplier.

Valve Outlet Pressure Settings by Elevation

Manifold Pressure Settings by Altitude for the UNITED STATES

Altitude		Natural Gas (inches w.c.)		Propane Gas (inches w.c.)
Feet	Meters	Single Stage and	Two Stage	Single Stage and	Two Stage
		Two Stage High Fire	Low Fire	Two Stage High Fire	Low Fire
0-2000	0-610	3.5	1.8	10.0	5.0
2001-3000	611-915	3.1	1.6	8.8	4.4
3001-4000	916-1220	3.0	1.5	8.5	4.2
4001-5000	1221-1525	2.8	1.5	8.1	4.1
5001-6000	1526-1830	2.7	1.4	7.7	3.9
6001-7000	1831-2135	2.6	1.3	7.4	3.7
7001-8000	2136-2440	2.5	1.3	7.1	3.5
8001-9000	2441-2745	2.4	1.2	6.7	3.4
9001-10000	2746-3045	2.3	1.2	6.7	3.4
	Manifold Pressure Settings by Altitude for CANADA
Altitude		Natural Gas (inches w.c.)		Propane Gas (inches w.c.)
Feet	Meters	Single Stage and	Two Stage	Single Stage and	Two Stage
		Two Stage High Fire	Low Fire	Two Stage High Fire	Low Fire
0-2000	0-610	3.5	1.8	10.0	5.0
2001-4500	611-1373	2.8	1.5	8.1	4.1

2.	Locate the 1/8” output pressure tap on the valve (See FIGURE 11). Turn the
	knob on the top of the valve to “OFF”. Connect a manometer to the 1/8" pipe
	outlet pressure tap in the valve. Use a water column manometer that is readable
	to the nearest tenth of an inch.
3.	Single Stage and Two Stage High Fire - Turn the knob on the top of the valve
	to “ON”. Remove the cap from the pressure adjusting screw and adjust the gas
	train pressure to the pressure selected from the table above. Adjust pressure by
	turning the regulator screw IN (clockwise) to increase pressure or OUT (coun-
	terclockwise) to decrease pressure.

Adjustment

1/8” Output

Two Stage Low Fire - Disconnect the wire from the “HI” terminal on the gas

Screw

Inlet

Pressure

Tap

Pressure Tap

valve and check the low fire pressure. Turn the regulator screw to adjust the

low fire outlet pressure to the “Low Fire” pressure selected from the table. Re-

connect the wire to the gas valve.

4. Turn up the thermostat. (NOTE: On Model UDAS, depress and hold the door

safety switch.) Cycle the burner once or twice to properly seat the adjustment

spring in the valve.

Re-check the pressure(s). When the outlet pressure is right for the installation,

Two -Stage Valve

Adjust High	Adjust Low
Pressure	Pressure
Output	Output

Inlet

Pressure

Tap 1/8” Output

Pressure

Tap

remove the manometer and replace the cap.

Check for leak at the pressure tap fitting.

5. With the heater operating determine that the inlet pressure to the heater for

natural gas is between 5 and 13.5 inches w.c. and for propane between 10 and

13.5 inches w.c. Take this reading as close as possible to the heater (Heaters are

equipped with gas valves that have an inlet pressure tap.) If the inlet pressure is

not within the specified range, the inlet pressure must be corrected and Steps 3

and 4 repeated.

6. Find the High Altitude Adjustment label in the plastic bag that contained these

instructions. Using a permanent marker, fill-in the appropriate information from

the tables on page 15. Select a location for the label on the outside of the heater

access panel so that it will be conspicuous to anyone operating or servicing the

unit. Be sure the surface is clean and dry and adhere the label.

Form RZ-NA I-UDA, P/N 195673 Rev 5, Page 14