SIT 840-843-845 SIGMA

M U LT I F U N C T I O N A L C O N T R O L
FOR GAS BURNING APPLIANCE

Application Main Features

Domestic gas appliances: Two automatic shut-off valves.
central heating boilers, combi Servo pressure regulator On/Off
boilers, instantaneous water (840), High/Low control (843) or
heaters, space heaters with with full electrical modulation
Subject to change without notice

automatic ignition system. (845).

Normative reference Versions

EN 126. 840 ON/OFF
Multifunctional devices for gas 843 High/Low
burning appliances. 845 Modulating
9.955.462 01

w w w . s i t g r o u p . i t

9955462_02_840-843-845_GB_catalo1 1 29/11/2010 9.10.57

 GENERAL DATA
Construction characteristics

• Aluminium body • Connection for pressure regulator/combustion

• Two shut-off gas valves chamber compensation
• Side outlet option • Two mounting holes
• Inlet filter • Torsion and bending resistance group 2
• Pilot outlet (optional)
• Outlet and pilot filters (optional)

• Inlet and outlet pressure test point

Use specifications

• Mounting position: any position

• Gas families: 1st, 2nd and 3rd
• Ambient temperature 0....60 °C (-20 °C....60 °C on request)
• Maximum inlet pressure 60 mbar

Mechanical Connections

• Gas inlet and outlet G 3/4 ISO 228

or: M4 (4) (flanges)
minimum full thread 6 mm
or: Rp 1/2 ISO 7 (105 mm version)

• Side Outlet M5 (3) (flanges)

minimum full thread 7 mm
• Pilot M10x1 for 4 mm, 6 mm or 1/4” tubing
• Pressure test point ø 9 mm
• Pressure compensation ø 7 mm

Electrical ConnectionS

• Automatic shut-off valves Male contact 3003 Molex compatible,

suitable for female Molex series 3001
• Electrical modulator male fast-on connector 2.8 x 0.8 mm

Electrical Data

Automatic shut-off valves EV1 EV2 EV1 EV2

Nominal Supply Voltage (AC) Current at nominal voltage (mA) Power at nominal voltage (W)

230 V 50 Hz Vac 40 12 4.3 2.0

24 V 50 Hz Vac 390 100 4.6 2.0
24 V 50 Hz RAC 270 115 6.5 2.8
Protection degree:
IP 40 with SIT NAC 504 connector. IP 44 with SIT NAC 504 connector and Gasket.
IP 40 or IP 44 with EV connector Serie 960.4.‑

9955462_02_840-843-845_GB_catalo2 2 29/11/2010 9.10.57

 DESCRIPTION
1 On-off solenoid valve EV1.
840 2 1
2 On-off solenoid valve EV2.

3 Inlet pressure test point. 5

4 Outlet pressure test point.

5 Connection for pressure regulator /

combustion chamber compensation.
3
6 Servo-pressure regulator. 4 6
7 Gas outlet pressure modulator.

8 Pilot outlet. 843 845 7

10
9 Main gas outlet.

10 Side outlet.

11 Slow opening device.

11 8
9

CONNECTION DIAGRAM ADJ

R.Q.

1 2 3 4
Vent

Pout P.R.A D J. Pin

EV2 EV1

9955462_02_840-843-845_GB_catalo3 3 29/11/2010 9.11.01

 FUNCTIONS
FUNCTIONS

• Automatic gas shut-off

On-off solenoid valve EV1 class A or B
On-off solenoid valve EV2 class C or J
Closing time ≤ 1 second

• Pressure regulation
Servo pressure regulator class B
with reference to EN 126

• Slow opening
Optional on 840 and 843
Adjustable version on request

• Gas outlet pressure electrical modulation

843 SIGMA
High/Low modulation (black coil)
Modulation Range 3-50 mbar
Nominal Supply Voltage 230 V 50 Hz Rectified AC
Protection Degree IP40 or IP44 with connector serie 960.4
Power 2.8 VA

845 SIGMA
Continuous modulation
Modulation range 1-37 mbar (modulator in horizontal position)
Electric Supply 9 V 310 mA (white coil)
17 V 165 mA (light blue coil)

40

30

845 Pressure/current characteristic

20

Tolerance band (increasing current).

10
Modulator axis in horizontal position.
0
0 50 100 150 200 250 300 350

Outlet pressure Pu [mbar] Outlet pressure Pu [mbar]

40 40

30 165 mA (17V) 30 310 mA (9V)

20 20

10 10

0 0
0 25 50 75 100 125 150 175 0 50 100 150 200 250 300 350

current [mA] current [mA]

40

30

 20

10

0
9955462_02_840-843-845_GB_catalo4 4 0 25 50 75 100 125 150 175 29/11/2010 9.11.02
 SYSTEMS
84X SIGMA - 579 DBC

Combined system - gas control/automatic

burner control suitable for either an appliance
with natural draught or fan assisted.

579 DBC Characteristics:

• Specifically designed for SIGMA gas control.
• Direct burner ignition (DBI) or by intermittent
pilot (IP).
• Manual or non-volatile lockout with reset and
indicator integrated or fitted remotely.

For further infomation see the specific technical sheet

579 DBC code 9.955.059

84X SIGMA - 504 NAC

Combined system gas control, connector with
integrated igniter.

504 NAC Characteristics:

• Connector with integrated igniter specifically
designed for SIGMA gas control.
• Protection degree IP40. IP44 available on
request.

For further infomation see the specific technical sheet

504 NAC code 9.955.457

Accessories
V
Main voltage electric supply connector (Z)

• 3 or 4 wires power versions available.

• Protection degree IP40 or IP44.

843 Modulator supply connector Z

• Integrated rectified circuit

• Protection degree IP40 or IP44

845 Modulator supply connector (V)

9955462_02_840-843-845_GB_catalo5 5 29/11/2010 9.11.04

 CAPACITY
FLOW RATE Q AS A FUNCTION OF PRESSURE DROP ∆P

solenoid valves class B+J solenoid valves class B+C

Q [m3/h d=0.55] Q [m3/h d=0.55]

10 10

8 840-843-845 HC 8 840-843-845 HC

6 6

4 845 4 845

2 2

0 0
2 4 6 8 10 2 4 6 8 10

∆P [mbar] ∆P [mbar]

flowrate at ∆p = 5 mbar

gas family 845 840-843-845

HC
B+J B+C B+J B+C
1st d=0.41 5.2 m3/h 4.4 m3/h 7 m3/h 4.6 m3/h

2nd d=0.55 4.5 m3/h 3.8 m3/h 6 m3/h 4 m3/h

3rd d=1.55 2.6 m3/h 2.3 m3/h 3.6 m3/h 2.4 m3/h

845 HC: High Capacity Version

9955462_02_840-843-845_GB_catalo6 6 29/11/2010 9.11.04

 CAPACITY
regulated flow rate q in accordance with en 126

845 845
solenoid valves class B+J solenoid valves class B+C

Q [m3/h] Q [m3/h]
12 12 12

10 8 10 10

8 7 8 8

6 L 6 6 L 6
H-E
4 5 4 4
H-E
2 4 2 2

0 3 0 0
6 8 10 12 14 16 5 10 15 6 20 8 25 10 12 14 16 6 8 10 12 14 16

Pu [mbar] Pu [mbar]

12
840-843-845 HC 840-843-845 HC
10 solenoid valves class B+J solenoid valves class B+C
3
8 Q [m /h] Q [m3/h]
12 12 12
6
10 10 8 10
4
8 8 7 8
2 L L
6 6 6 6
0 H-E
4 6 8 10 12
4 14 16 5 4 H-E

2 2 4 2

0 0 3 0
6 8 10 12 6 14 8 16 10 12 514 10
16 15 6 20 8 25 10 12 14 16
Pu [mbar] Pu [mbar]

Second Family Group H, E and L

Inlet pressure range (mbar)

Nominal Max Min Relative

Density

H-E 20 25 17 0.555
L 25 30 20 0.612

Minimum flowrate 0.3 m3/h d=0.55

845 HC: High Capacity Version

9955462_02_840-843-845_GB_catalo7 7 29/11/2010 9.11.05

 OPERATION PRINCIPLE

840
845
EV1 EV2

Electrical
modulator Connection for pressure
Inlet pressure
governor/combustion
chamber compensation

Outlet
pressure

Pressure
regulator

Pilot
Intermediate
chamber

SIGMA has two automatic solenoid shut-off valves.

• When the solenoid (EV1) is energised the first gas valve opens.
• The second solenoid (EV2) allows the gas to flow through the servo circuit. The
pressure under the main servo diaphragm increases and consequently the servo valve
opens.
In case of gas or power supply failure the spring pressure assures the automatic closure of the
gas valves.
The outlet pressure regulation is performed by the servo system.
When the outlet pressure is greater than the value driven by the modulator, the pressure
regulator valve opens and as a consequence the pressure under the main servo diaphragm
decreases closing the main valve. Therefore the outlet pressure goes back to the preset value.
Vice versa if the outlet pressure is smaller than the preset level the pressure regulator closes
and therefore the servo pressure increases opening the main valve.

9955462_02_840-843-845_GB_catalo8 8 29/11/2010 9.11.05

 Slow Opening

An extra chamber with diaphragm and spring

are inserted on 840 SIGMA. 840

When the EV2 opens the servo circuit the gas

enters in the slow-opening chamber. The gas
pressure under the main valve diaphragm goes
to a certain level and partially opens the gas
way. The pressure is not increased because of
the movement of the slow opening diaphragm.

In the adjustable slow opening version, After a certain time, the slow-ope-
by using the proper regulating screw, the ning spring is completely compressed
pressure rise and the opening time can be and therefore there is no more volu-
changed between set limits. me variation and the pressure under
the main diaphragm increase rapidly,
completely opening the main valve.

Pout (mbar)
16

1
270°
1

10
180°
8

 0°
0 t (sec)
0 1    5 6 7 8 9 10

9955462_02_840-843-845_GB_catalo9 9 29/11/2010 9.11.07

 840 OUTLET PRESSURE ADJUSTMENT
All adjustments must be made on the basis of the
specific characteristics of the appliance. Check
A
inlet and outlet pressure using the pressure test
points provided. After testing, carefully seal test
points with the provided screws. Recommended
torque: 1.0 Nm.
B Disconnect pressure regulator connection “VENT”
(if used).
Remove the protective plug A.
Screw in the screw B to increase the pressure and
screw it out to decrease it.
After setting put back the protective plug.

843/845 OUTLET PRESSURE ADJUSTMENT

All adjustments must be made on the basis of the
specific characteristics of the appliance. Check
E inlet and outlet pressure using the pressure test
points provided. After testing, carefully seal test
points with the provided screws. Recommended
torque: 1.0 Nm.
D Disconnect pressure regulator connection “VENT”
C
(if used).
Remove the modulator plastic cap E.

• Maximum pressure: power the modulator in the

maximum condition. Screw in the nut C to increase
the outlet pressure and screw it out to decrease it.
Use a 10 mm spanner.

• Minimum pressure: Turn off the power supply to

the modulator and, keeping the nut C stationary,
845 screw in the screw D to increase the pressure and
Outlet pressure Pu [mbar] screw it out to decrease it. Screwdriver 6 x 1 blade.
Carefully put back the modulator plastic cap.
40
MAX Reconnect pressure regulator connection (if used).
30
WARNING: to ensure the correct operation of the
20 modulator it is necessary that the plastic cap E is
returned to its original location.
10

MIN 0
0 50 100 150 200 250 300 350

current [mA]

10

9955462_02_840-843-845_GB_catalo10 10 29/11/2010 9.11.08

 840 DIMENSIONS
Gas connection: G3/4 ISO 228

11

9955462_02_840-843-845_GB_catalo11 11 29/11/2010 9.11.08

 840 DIMENSIONS
Gas connection: Flanges
inlet and outlet connection
Optional Rp 1/2 ISO 7
105 mm version
80 mm version

12

9955462_02_840-843-845_GB_catalo12 12 29/11/2010 9.11.09

 840 DIMENSIONS Slow Opening VERSION
Gas connection: G3/4 ISO 228

13

9955462_02_840-843-845_GB_catalo13 13 29/11/2010 9.11.10

 843/845 DIMENSIONS
Gas connection: G3/4 ISO 228

14

9955462_02_840-843-845_GB_catalo14 14 29/11/2010 9.11.11

 843/845 DIMENSIONS
Gas connection: Flanges

Rp 1/2 ISO 7 version

available on request
105 mm version
80 mm version

15

9955462_02_840-843-845_GB_catalo15 15 29/11/2010 9.11.11

 SIT La Precisa S.p.A.
Viale dell’Industria 31-33
35129 PADOVA - ITALY
Tel. +39/049.829.31.11, Fax +39/049.807.00.93
www.sitgroup.it - e-mail: mkt@sitgroup.it

9955462_02_840-843-845_GB_catalo16 16 29/11/2010 9.11.11