Engineered air DG series Manual de usuario descargar pdf (Pagina 6)

Page 2

Recently there has been the introduction of a servo-motor that is being used to modulate the

gas flow. The servo-motor operates a modified Neo valve. This will reduce hunting of the gas

modulating valve but it will not totally eliminate it. There will be a separate shutoff device

such as the Honeywell V4055.

3. The nature of the DG burner does not allow it to go to a high turndown ratio. For this reason

it is necessary to control temperature rise at the low end of the burner by cycling the burner

on and off. After the 109 has modulated the burner to low fire, it will keep the contacts

between 8 and 9 closed for about 1 ½ minutes. This is to allow the discharge control to

modulate the burner just above low fire if required. If temperature rise is too high to “lock on”

to a low fire control point, the relay contacts between 109 terminals 8 and 9 will then open.

This shuts off the main control valve. Note that if the discharge control call for the modulating

valve to open above low fire after the valve has modulated back to low fire, this cancels any

timing that has begun. The 109 will begin the full 1½ minute timing again each time the

signal drives to low fire.

4. Once the heat call has been completed and the 109 has timed out, the next call for heat will

begin at point 1 above. The 109 will allow a large number of ignitions to occur on the DG

unit, especially when it is cycling at minimum firing condition. There can be ignitions

occurring every 2 minutes. If one ignition fail, the flame supervision relay will lock out. This

will require manual resetting of the flame relay.

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Engineered air DG series Manual de usuario Pagina 6