VAD, VAG (GB) - System Control Engineering

Governor with solenoid valve VAD 

Air/gas ratio control with solenoid 

valve VAG 

All-purpose servo-governor for gaseous media with 

integrated safety valve 

Suitable for a max. inlet pressure of 500 mbar 

Outlet pressure up to 100 mbar 

Suitable for intermittent operation 

Easy installation L1 into (+) a system 

Minimum installation effort: no external impulse line 

required 

Check indication by blue LED 

High control quality N (–) 

Precise setting options from two sides 

3.1.0.4 Technical Information · Edition 3.04 GB

Table of Contents 

Governor with solenoid valve VAD Air/gas ratio 

control with solenoid valve VAG . . . . . . . . . . . . 1 

Table of Contents . . . . . . . . . . . . . . . . . . . . . . . . 2 

Application . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3 

Application examples . . . . . . . . . . . . . . . . . . . . . . 4 

Constant pressure control . . . . . . . . . . . . . . . . . . . . . . .4 

Constant pressure control with two solenoid valves . . .4 

Constant pressure control with max. pressure switch . .5 

Constant pressure control with non-controlled pilot gas 

outlet . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .5 

Modulating control with two solenoid valves . . . . . . . . .6 

Modulating control . . . . . . . . . . . . . . . . . . . . . . . . . . . .6 

High/Low control . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .7 

Modulating control with two solenoid valves and inlet 

pressure switch . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .7 

Certification . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8 

Function . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9 

Governor for gas VAD . . . . . . . . . . . . . . . . . . . . . . 9 

Air/gas ratio control VAG . . . . . . . . . . . . . . . . . . . 10 

VAD, VAG connection diagram . . . . . . . . . . . . . . 11 

Replacement possibility for MODULINE 

governors with solenoid valve . . . . . . . . . . . . . 12 

Flow rate . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14 

Selection example for VAD . . . . . . . . . . . . . . . . . 14 

Selection example for VAG . . . . . . . . . . . . . . . . . 15 

Selection . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16 

Project planning information . . . . . . . . . . . . . . 18 

Installation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18 

Accessories . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20 

Pressure switch for gas DG..C . . . . . . . . . . . . . . 20 

Bypass valve VAS 1 . . . . . . . . . . . . . . . . . . . . . . 20 

Technical data . . . . . . . . . . . . . . . . . . . . . . . . . . 21 

VAD . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 21 

VAG . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 21 

Dimensions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22 

Maintenance cycles . . . . . . . . . . . . . . . . . . . . . 23 

Contact . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 24 

VAD, VAG · Edition 3.04 

= To be continued, = End of chapter 

2

VAD 

Application 

Governor VAD and air/gas ratio control 

VAG incorporating servo technology 

for shut-off and precise control 

of the gas supply to gas burners and 

gas appliances. For use in gas control 

and safety systems in all sectors 

of the iron, steel, glass and ceramics 

industries, also in commercial heat 

generation, such as the packaging, 

paper and foodstuffs industries. 

VAG 

VAD: Constant governor, Class 

A, with high control accuracy, for 

excess air burners, atmospheric 

burners or single-stage force draught 

burners. Pressure preset via setpoint 

spring. 

VAG: Air/gas ratio control, Class A, 

for maintaining a constant air/gas 

pressure ratio for modulating-controlled 

burners or with VAS 1 bypass 

valve for step-by-step-controlled 

burners. Pressure preset by the air 

control line. 

The VAG can also be used as a zero 

governor for gas engines. 

Easy-to-service 

measuring connections. 

VAD: Gas outlet 

pressure p G 

VAG: Also air control 

pressure p L 


3

Application 


Application examples 

Constant pressure control 

The governor with solenoid valve VAD 

maintains the set gas outlet pressure 

p G constant when subject to differing 

flow rates. If a second solenoid 

valve is used upstream of the VAD, 

this complies with the requirements 

of EN 746-2 for two Classe A valves 

connected in series. 

VAS 


Constant pressure control with 

two solenoid valves 

The governor with solenoid valve VAD 

maintains the set gas outlet pressure 

p G constant when subject to differing 

flow rates. The gas line is two Class 

A shut-off valves connected in series, 

in accordance with the requirements 

of EN 746-2. 

 


4

Application 


DG..C min. 

VAS 

DG..C max. 


max. pressure switch 

In this example, the minimum inlet 

pressure p e and the maximum outlet 

pressure p G are monitored with the 

pressure switches DG..C. The simple 

attachment of the pressure switch 

module makes installation easier. 


DG..C min. 

VAS 


VAS 1 

DG..C max. 


non-controlled pilot gas outlet 

In this application, the pilot burner is 

supplied with a high inlet pressure 

via the pilot gas outlet. Here as well, 

the simple attachment of the bypass 

valve module makes installation 

easier. The minimum inlet pressure 

p e and the maximum outlet pressure 

p G are monitored with the pressure 

switches DG..C. 

 


5

Application 


IC 

 

BVA 


p L 

Modulating control 

The gas outlet pressure p G is controlled 

via the air/gas ratio control 

with solenoid valve VAG. The gas 

outlet pressure p G follows the changing 

air control pressure p L . The ratio 

of gas pressure to air pressure remains 

constant. The VAG is suitable 

for a control range up to 10:1. 

If a second solenoid valve is used 

upstream of the VAG, this complies 

with the requirements of EN 746-2 

for two Class A valves connected 

in series. 

 

 

 

 

 

 

Modulating control with two 

solenoid valves 

The gas outlet pressure p G is controlled 

via the air/gas ratio control 

with solenoid valve VAG. The gas 

outlet pressure p G follows the changing 

air control pressure p L . The ratio 

of gas pressure to air pressure remains 

constant. The VAG is suitable 

for a control range up to 10:1. 

The gas line is two Class A shut-off 

valves connected in series, in accordance 

with the requirements of 

EN 746-2. 

 


6

Application 


 

 

 

Modulating control with two 

solenoid valves and inlet pressure 

switch 

In this case, the minimum inlet 

pressure p e is monitored by the 

pressure switch DG..C. The simple 

attachment of the pressure switch 

module makes installation easier. 

 

 

 

 

 

 

 

 

 

High/Low control 

At high fire, the gas outlet pressure 

p G follows the air control pressure 

p L . The ratio of gas pressure to air 

pressure remains constant. Low fire 

is determined via the bypass valve. 

Here as well, the simple attachment 

of the bypass valve module makes 

installation easier. 

 

 

 


7

Certification 

EC type-tested and certified 

pursuant to 

– Gas Appliances Directive 

(90/396/EEC) in conjunction with 

EN 161, EN 88 and EN 126, 

– Machinery Directive 

(89/392/EEC), 

– Low Voltage Directive 

(73/23/EEC) in conjunction with 

the relevant standards, 

– EMC Directive (89/336/EEC) in 

conjunction with EN 55014. 

FM, UL and CSA approval in preparation. 


8

Function 

The governor is closed when it is disconnected 

from the power supply. 

Opening: Alternating voltage is applied 

and fed to the solenoid coil via 

a rectifier with a suppressor circuit. 

The blue LED lights up. The coil’s 

magnetic field pulls the armature 

upwards and clears the supply 

nozzle for the gas inlet pressure p e . 

The gas passes through the internal 

impulse tube to the adjustment diaphragm 

and then pushes the valve 

seat open. The outlet pressure is applied 

to the servo-diaphragm via the 

internal bypass. The servo-governor 

then maintains a set constant outlet 

pressure p G . 

Governor for gas VAD 

The nominal outlet pressure p G is 

defined by the control spring. 

 


9

Function 

Air/gas ratio control VAG 

The air/gas ratio control VAG controls the outlet pressure p G equal to the 

variable air control pressure p L . The ratio of gas pressure to air pressure 

remains constant: 1:1. 

The VAG is suitable for a control range up to 10:1. 

p L 


10

Function 

VAD, VAG connection diagram 

L1 (+) 

N (–) 


11

Replacement possibility for MODULINE governors with solenoid valve 

GVS, GVI and GVIB are to be replaced by VAD, VAG and VAG+VAS 

GVS Governor with solenoid valve Governor with solenoid valve VAD 

GVI Air/gas ratio control with solenoid valve Air/gas ratio control with solenoid valve VAG 

GVIB 

Air/gas ratio control with solenoid valve 

and bypass valve 

Air/gas ratio control with solenoid valve 

and bypass valve 

VAG+VAS 

3 

/8 Size 1, DN 15 or 25, Rp 3 /8 on request 

115 1⁄2 Size 1, DN 15 or 25, Rp 1⁄2 Size 1 DN 15 115 


1 Size 1, DN 15 or 25, Rp 1 Size 1 DN 25 125 

232 1 Size 2, DN 32 or 40, Rp 1 


350 

11⁄2 

Size 3, DN 50, Rp 11⁄2 

2 Size 3, DN 50, Rp 2 Size 3 DN 50 350 

ML 

MODULINE + connection flanges Rp internal thread 

R 

Rp internal thread 

01 Max. inlet pressure p e max. : 100 mbar Max. inlet pressure p e max. : 500 mbar 

02 200 mbar 500 mbar 

Quick opening Quick opening /N 

K Mains voltage: 24 V DC Mains voltage: 24 V DC K 

Q 120 V AC 120 V AC Q 

T 220/240 V AC 230 V AC W 

 


12

Replacement possibility for MODULINE governors with solenoid valve 

Cont. 

3 Electrical connection via terminals Electrical connection via terminals 

6 Electrical connection via standard socket on request 

S Position indicator on request 

G Position indicator with gold contacts on request 

M Suitable for biologically produced methane Suitable for biologically produced methane 

Pressure test point at the inlet Pressure test point at the inlet and outlet* 

Outlet pressure p G : 2.5 – 25 mbar -25 

Outlet pressure p G : 2 – 90 mbar 5 – 50 mbar -50 

10 – 100 mbar -100 

Standard seat 

A 

GVS 115ML01T3 Example Example VAD 125R/NW-100A 

with Rp 1 connection flanges 

with test points 

standard, available 

* Pressure test points may be attached at the left 

and/or right-hand side. 


13

∆p [mbar] 

500 

400 

300 

200 

100 

80 

60 

50 

40 

30 

20 

10 

8 

5 

3 

VAD, VAG 115..B 

VAD, VAG 125..A 


P3 

 

P2 

 


P1 

 

Selection example for VAD 

Natural gas 

Inlet pressure p e = 100 mbar 

Outlet pressure p G = 40 mbar 

Flow rate V . max = 50 m 3 /h 

The selected control ratio from 

high-fire to low-fire rate is Rv = 5:1 

High fire 

Δp = p e - p G = 60 mbar 

Point P1 

Select: VAD 125..A 

Low fire 

V . G min = V. G max = 10 m 

Rv 

3 /h 

Δp = p e - p G = 60 mbar 

Point P2 

Select: VAD 125..A 

1 

2 

3 

2 

0,3 0,4 0,6 1 2 3 4 5 8 10 20 30 40 60 100 200 

0,2 0,3 0,5 0,8 1 2 3 4 5 8 10 20 30 40 60 100 

0,3 

0,5 0,8 1 2 3 4 5 8 10 20 30 40 

Flow rate 

The characteristic flow rate curves 

have been measured with the specified 

flanges and a fitted strainer. If 

two or more valves are combined 

the pressure loss per individual valve 

drops by approx. 5%. 

= Natural gas 

= LPG 

= Air 

60 100 

200 

V' [m 3 /h (n)] 

Point P1 and point P2 must be 

within the working range of a unit 

size. We recommend that you select 

the smallest size to achieve the best 

control properties. 


14

∆p [mbar] 

1 

2 

3 

500 

400 

300 

200 

100 

80 

60 

50 

40 

30 

20 

10 

8 

5 

3 

2 

0,3 0,4 0,6 1 2 3 4 5 8 10 20 30 40 60 100 200 

0,2 0,3 0,5 0,8 1 2 3 4 5 8 10 20 30 40 60 100 

0,3 

VAD, VAG 115..B 



P3 

 

P2 

 


P1 

 

0,5 0,8 1 2 3 4 5 8 10 20 30 40 

60 100 

200 

V' [m 3 /h (n)] 

Selection example for VAG 

Natural gas 

Inlet pressure p e = 100 mbar 

Outlet pressure p G max = 40 mbar 

Flow rate V . max = 50 m 3 /h 

The selected control ratio from 

high-fire to low-fire rate is Rv = 5:1 

High fire 

Δp = p e - p G max = 60 mbar 

Point P1 

Select: VAG 125..A 

Low fire 

p G min = p G max 

Rv 2 = 1.6 mbar 

V . G min = V. G max = 10 m 

Rv 

3 /h 

Δp = p e - p G min = 98.4 mbar 

Point P3 

Select: VAG 125..A 

Point P1 and point P3 must be 

within the working range of a unit 

size. We recommend that you select 

the smallest size to achieve the best 

control properties. 


15

Selection 

VAD: Governor with solenoid valve / VAG: Air/gas ratio control with solenoid valve 

– 15 20 25 32 40 50 /–* /15 /20 /25 /32 /40 /50 R /N K Q W -25 -50 -100 A B K E 

VAD 1 



VAG 1 



Inlet flange nominal size 

– = no inlet flange 

Outlet flange nominal size 

/– = no outlet flange* 

Specification may be omitted if outlet = inlet 

Rp internal thread = R 

Quick opening, quick closing = /N 

Mains voltage: 24 V DC = K 

120 V AC; 50/60 Hz = Q 

230 V AC; 50/60 Hz = W 

Max. outlet pressure p G max. for VAD: 2.5 to 25 mbar = -25 

5.0 to 50 mbar = -50 

10 to 100 mbar = -100 

Standard valve seat = A 

Reduced valve seat = B 

Connection kit VAG for air control pressure p L : 1 plastic hose coupling, 2 screw plugs = K 

1 compression fitting, 2 test points p G and p L = E 

Accessories attached at the right-hand side: 2 screw plugs 

2 test points p e and p G 

Gas pressure switch DG..C (see table) at the inlet 

Gas pressure switch DG..C (see table) at the outlet 

Bypass valve VAS 1 

Accessories attached at the left-hand side: 2 screw plugs 

2 test points p e and p G 

Gas pressure switch DG..C (see table) at the inlet 

Gas pressure switch DG..C (see table) at the outlet 


* Bei einer Bestellung muss angeben werden, an welchen Ausgangsflansch der Druckregler angebaut wird. GB GB GB GB 

Order example 

 


VAG 125R/NWAK, 2 screw plugs attached at the right-hand side 

2 test points attached at the left-hand side 

= standard 

= available 

16

Selection 

Pressure switch for gas DG..C 

Type Adjusting range 

[mbar] 

DG 17/VC 2 – 17 

DG 40/VC 5 – 40 

DG 110/VC 30 – 110 

DG 300/VC 100 – 300 

 


17

Project planning information 

The inlet pressure p e and the outlet 

pressure p G can be measured on 

both sides of the valve body. 

VAD: Measurement point for the gas outlet 

pressure p G on the governor body. 

> 20 

mm 

The VAD, VAG may not be in contact 

with masonry. Minimum clearance 

20 mm. 

p e 

p G 

p G 

p L 

VAG: Additional measurement point 

for the air control pressure p L on the 

governor body. 

VAD, VAG: To increase the control 

accuracy, an external impulse line 

can be connected to the pressure 

test point p G . 

a a 

GFK 

GFK 



Ensure that there is sufficient installation 

space around the flange screws 

and the actuator. 

Sealing material and thread cuttings 

must not be allowed to get into the 

valve housing. 

We recommend that a filter be installed 

upstream of every system. 

Installation 

Installation position vertical or horizontal, 

not upside down. 

> +80 ° C 

The solenoid body heats up during 

operation – up to 90°C depending on 

ambient temperature and voltage. 

To ensure that the air/gas ratio control 

VAG can react quickly when 

the load is changed, the impulse 

line p L should be kept as short as 

possible. 

Do not store or install the unit in the 

open air. 

 


18

Project planning information 

Installation 

If more than three valVario controls 

are installed in line, the controls must 

be supported. 


19

pe 

 

Accessories 

Pressure switch for gas DG..C 

Scope of delivery: 

1 x pressure switch for gas, 

2 x retaining screws, 

2 x sealing rings. 

Monitor the inlet pressure p e : The plug of the pressure 

switch for gas DG..C points towards the inlet flange. 

Monitor the outlet pressure p G : The plug of the pressure 

switch for gas DG..C points towards the outlet flange. 

1 

2 

3 

4 

5 


Delivery for VAS 1 attached to VAD 1, VAG 1: 

1 1 x bypass valve VAS 1 / 

2 1 x connection pipe, 1 x sealing stopper, if the bypass valve at the 

outlet side has a threaded flange, or 2 x connection pipes, if the bypass 

valve has a dummy flange at the outlet side / 

3 4 x O-rings / 4 4 x double nuts / 5 4 x connection parts. 

1 

2 

3 

4 

5 

Delivery for VAS 1 attached to VAD 2, VAD 3, VAG 2, VAG 3: 

1 1 x bypass valve VAS 1 / 

2 1 x connection pipe, 1 x sealing stopper, if the bypass valve at the 

outlet side has a threaded flange, or 2 x connection pipes, if the bypass 

valve has a dummy flange at the outlet side / 

3 4 x O-rings / 4 4 x washer / 5 4 x connection parts. 


20

Technical data 

Types of gas: Natural gas, town 

gas, LPG (gaseous), biologically 

produced methane (max. 0.1 %-byvol. 

H 2 S); other gases on request. 

The gas must be dry in all temperature 

conditions and must not 

condense. 

Inlet pressure range p e : 

10 – 500 mbar. 

Opening time of the solenoid valve: 

Quick opening: ≤ 0.5 s. 

Closing time: 

Quick closing: < 1 s. 

Ambient temperature: 

-20 – 60°C, no condensation permitted. 

Class A safety valve pursuant to 

EN 161. 

Control class A to EN 88. 

Control range: up to 10:1. 

Mains voltage: 

230 V AC, +10/-15%, 50/60 Hz; 

120 V AC, +10/-15%, 50/60 Hz; 

24 V DC, +20/-20%. 

Cable gland: 

M 20 x 1.5. 

Power consumption: 

Type 24 V DC 120 V AC 230 V AC 

[W] [W] [W] 

VAD/VAG 1 25 32 35 



Enclosure: IP 65. 

Duty cycle: 100%. 

Power factor of the solenoid coil: 

cos ϕ = 1. 

Valve housing: Aluminium, 

Valve seal: NBR. 

Connection flanges with internal 

thread: Rp to ISO 7-1. 


Outlet pressure p G : 2.5 – 25 mbar, 

5.0 – 50 mbar, 

10 – 100 mbar. 


Outlet pressure p G : 0.5 – 100 mbar. 

Adjusting range at min. flow: 

±5 mbar. 

Transmission ratio of gas to air: 

1:1 

The inlet pressure must always be 

higher than the air control pressure. 

Connection of the air control pressure 

p L : 

1 1/8” coupling for plastic hose (internal 

dia. 3.9, external dia. 6.1) or 

1 compression fitting for tube 6x1. 

 


21

Dimensions 

Type Connection Dimensions Weight 

 

 

 

 

 

L E F H1 H2 

Rp DN mm mm mm mm mm kg 

VAD, VAG 115 1/ 2 15 75 75 15 140 82 1.8 

VAD, VAG 120 3/ 4 20 91 75 23 140 82 1.9 

VAD, VAG 125 1 25 91 75 23 140 82 1.9 


VAD, VAG 232 1 1 / 4 32 127 88 29 164 112 4.3 






 

VAD, VAG 

21,5 79 

48 

36 

DG..C 


22

Maintenance cycles 

Once per year, 

twice per year in the case of biologically 

produced methane. 

If the flow rate drops, clean the 

strainer. 


23

Contact 

G. Kromschröder AG 

Strotheweg 1 

D-49504 Lotte (Büren) 

Tel.: +49 (0)5 41 / 12 14 - 0 

Fax: +49 (0)5 41 / 12 14 - 370 

info@kromschroeder.com 

The current addresses of our international agents are available on the Internet: 

www.kromschroeder.com information contacts 


24

VAD, VAG (GB) - System Control Engineering

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