Honeywell V8944C Manuale Utente

65-0214—08

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The V4943/V8943B,C,N Valves are combination gas controls 

that include a single stage of pressure regulation in addition to 

the shut-off function. They have a single solenoid and a single 

regulating diaphragm. 

When the controller is not calling for heat, the valve solenoid 

coil is not energized. Static gas inlet pressure and a spring act 

together to close the valve. In this condition, a three-way servo 

valve directs inlet pressure directly above the main diaphragm, 

creating static pressure on both sides of the main diaphragm.

On a call for heat, the controller contacts close and the valve 

solenoid coil is energized, opening the servo valve and 

allowing the gas that is above the main diaphragm to bleed 

downstream, and diverting inlet (supply) gas through a supply 

orifice. This reduces the pressure above the diaphragm, and 

the gas that is bled off flows through a regulating valve to the 

outlet of the gas valve. The pressure differential across the 

main diaphragm is greater than the spring force, so the valve 

opens. The valve opening rate is controlled by a timing orifice 

through which the bleed gas passes.

Once the valve is open, outlet pressure is sensed through the 

bleed passage. The outlet pressure acts on the regulating 

(servo) diaphragm and tends to open or close the integral 

regulating valve until a force balance is established between 

the outlet pressure acting on the servo diaphragm and the 

regulator spring that acts on the atmospheric side of the servo 

diaphragm. 

The system is balanced when the flow of supply gas through 

the supply orifice is equal to the outflow of gas through the 

regulating valve. The regulated output pressure required to 

achieve equilibrium is varied by increasing or decreasing the 

spring force acting on the atmospheric side of the regulating 

diaphragm. Pressure adjustment is done through the use of a 

threaded nylon screw acting on the regulating spring. 

Regulator springs with different spring rates provide the 

various ranges of pressure regulation needed for natural and 

LP gases.

After the controller is satisfied, the procedure is reversed. The 

controller contacts open and the solenoid coil is de-energized. 

The plunger is released, moving to the down position. The 

servo valve closes, diverting supply gas away from the orifice 

and allowing the gas inlet pressure to act directly above the 

main diaphragm. The resulting increase in upper chamber 

pressure, along with the main spring, forces the main 

diaphragm against the valve seat, stopping the gas flow.

In the event of a power failure during automatic operation of the 

valve, the V4943/V8943B,C,L,N Valve servo valve closes, 

diverting supply gas away from the orifice and allowing the gas 

inlet pressure to act directly on the main diaphragm. The 

change in upper chamber pressure, along with the main 

spring, forces the main diaphragm against the valve seat, 

stopping the gas flow. Normal operation will resume upon the 

restoration of power. 

These models use two pressure regulators (low fire and high 

fire) and two solenoids to provide two distinct stages of 

pressure regulation. The first stage pressure regulator solenoid 

activates the same quick-close orifice valve and servo valve as 

in the V4943/V8943 models, but the bleed gas now flows 

through a first stage (low fire) regulator valve to the outlet. This 

maintains the outlet at a pressure controlled by the low fire 

regulator. The second stage regulator (high fire) is set to a 

higher outlet pressure. When the second stage solenoid is 

energized, gas is shunted past the low fire regulator through a 

timing orifice. The increased flow of supply gas (due to the 

second servo valve opening) further reduces the pressure 

above the main diaphragm, causing it to open more. The 

corresponding increase in outlet pressure forces the low fire 

regulator closed, and the valve regulates off the high fire 

regulator. 

The V4944/V8944L and N models use a timing orifice that 

gives an opening time to low fire of less than six seconds. The 

slower opening V4944/V8944B and C use timing orifices that 

give an opening time of three to 25 seconds.

Both regulators can be adjusted separately and the springs are 

sized so that the highest achievable pressure of the low 

pressure regulator range is less than the lowest achievable 

pressure of the high fire pressure regulator. The high fire 

setpoint cannot be achieved without the first stage solenoid 

being energized. 

Valve closing operation is identical to that described for V4943/

V8943B,C,N valves. 

Do not let fuel accumulate in the combustion chamber. 

If fuel is allowed to enter the chamber for longer than a 

few seconds without igniting, an explosive mixture 

could result.

1. Do not put the system into service until you have 

satisfactorily completed all applicable tests 

described in the Checkout section of the instructions 

for the flame safeguard control, and any other tests 

required by the burner manufacturer. 

2. Close all manual fuel shutoff valves as soon as 

trouble occurs.