How to choose the right solenoid valve for the detector (G1/2", G3/4", G1")
Why choosing a solenoid valve is just as important as choosing the detector itself
When designing a gas leak safety system, most attention is focused on the detector itself – its sensitivity, type of sensor, placement. The solenoid valve, which is commanded by the detector to shut off the gas supply, is often considered a "supplement" that is bought at the last minute, depending on what is currently in stock. This is a mistake that is paid for in practice – either in the form of unnecessarily high pressure loss on an oversized pipe, or conversely, in the form of a valve that physically cannot pass enough gas for the connected appliances, causing underpressure, incomplete combustion in the boiler, or even its failures.
A solenoid valve connected to a gas detector is the last safety link in the chain: the sensor evaluates the gas concentration in the air, the electronics evaluate the limit exceeded (typically 10 % and 20 % of the lower explosive limit – LEL) and in the event of an alarm, it cuts off the power supply to the valve coil, which closes mechanically and physically cuts off the gas supply to the area. If the valve is poorly dimensioned, the wrong type is chosen (NC/NO), or the thread does not match the existing pipe, the entire safety chain loses its meaning regardless of how good the detector itself is.
In this article, we will look at how to correctly choose a solenoid valve with a G1/2", G3/4", or G1" thread for a gas detector, what to pay attention to when dimensioning, what type of valve (NC vs NO) is suitable for a safety application, and how these components are actually mounted and connected. If you are dealing with the selection of the detector itself, we recommend our separate articles How to choose a gas leak detector for a household and industry and Gas detector with solenoid valve vs standalone detector: what to choose.
What is a solenoid valve and how it works with a detector
A solenoid (electromagnetic) valve is a closing element controlled electrically by a coil (solenoid). When voltage is applied to the coil, a magnetic field is created, which lifts or pulls down a metal core (piston) against a spring and opens or closes the medium passage through the valve. For safety applications related to gas leak detection, almost exclusively the version is used that is open in the normal (powered) state and closes automatically by the spring when the power is cut off – this principle is called "fail-safe" or "de-energized to close".
This means that:
- In normal operation, the valve coil is constantly under voltage and the valve is open, gas flows freely to the appliances.
- When the set gas concentration is exceeded (usually the second alarm level, 20 % LEL), the detector's control unit disconnects the valve's power supply.
- The valve closes immediately without current – mechanically, by the spring, independently of whether the electronics continue to function.
- In the event of a power failure of the entire system (e.g., the electricity in the building fails), the valve also automatically closes – which is a desirable safety behavior, because without electricity, you also lose the functionality of detection, and the preventive closure of gas is the correct solution in such a case.
That is why atria.sk offers detectors directly in a set with a solenoid valve – for example, Gas detector AVANSA 100M + solenoid valve G1/2" DN15, Gas detector AVANSA 100M + solenoid valve G3/4", DN 20 or Gas detector AVANSA 100M + solenoid valve G1" DN25 – where the compatibility of electrical parameters and function is pre-verified by the manufacturer, and the installer only needs to choose the correct size according to the pipe.
Cross-section of the valve – what it consists of and where the pressure loss occurs
The key structural elements that influence the choice of a specific model are: the seat diameter (determines the maximum flow and pressure loss), the sealing material (must be resistant to natural gas or propane-butane), the body material (usually brass or aluminum alloy), and the sealing class of the coil (IP54 to IP65 according to the installation environment).
How to correctly determine the diameter and thread of the valve – G1/2", G3/4", G1"
The most common mistake when ordering is the simplification "what thread the existing pipe has, that is the valve I will buy". The thread must of course match the pipe (or a reducer is used), but the decisive parameter is the actual gas flow that will pass through the valve at full power of all connected appliances. A valve with the correct thread but incorrectly dimensioned flow coefficient Kv can cause unnecessary pressure loss, which will manifest as insufficient boiler performance, burner flame fluctuations, or a gas pressure fault message on the boiler.
Approximate table for selection according to appliance power
| Thread / DN | Typical Kv (m³/h) | Approximate max. power for natural gas | Typical use |
|---|---|---|---|
| G1/2" – DN15 | approx. 2.2 – 3.0 | up to approx. 35-45 kW | apartment boiler, family house, small business |
| G3/4" – DN20 | approx. 3.5 – 4.5 | up to approx. 60-90 kW | larger house, small boiler room, restaurant kitchen |
| G1" – DN25 | approx. 5.5 – 7.0 | up to approx. 120-150 kW | apartment building boiler room, industrial facility, multiple appliances |
The values given are approximate and vary according to the specific manufacturer and type of medium (natural gas has a different density than propane-butane, which slightly changes the flow characteristics at the same Kv). An accurate calculation should be based on the total installed power of the appliances in the given area, the operating pressure of the gas (low pressure distribution up to 5 kPa in households, medium pressure in industry) and the maximum allowed pressure loss on the valve, which is usually set by the gas connection designer.
Practical example from a typical order
A residential building with a boiler room in the basement, two condensing boilers of 60 kW each, totaling 120 kW of installed power. The original pipe is dimensioned for G1". At first glance, it might seem that ordering a G3/4" valve is sufficient, because "after all, it's a small boiler room". In reality, at this power and given operating pressure, a G1" DN25 valve is needed. Otherwise, during simultaneous operation of both boilers, a pressure loss occurs, which is manifested by a low gas pressure error message on the second boiler exactly at the time of highest heat demand. This is one of the most common complaint scenarios we encounter in practice – most often the valve itself is not faulty, but it was chosen based on the thread of the existing pipe without calculating the actual flow rate.
On the contrary, in a family house with a 24 kW boiler, a G1" valve is completely oversized – it is not only more expensive, but its installation will require reductions on both sides, which means more sealing joints and theoretically more places where a leak could occur. In this case, a set with a G1/2" DN15 valve is fully sufficient.
NC or NO valve – why it matters in a safety application
In the terminology of solenoid valves, we commonly encounter the designations NC (normally closed) and NO (normally open), which refer to the state of the valve without electrical power:
- NC valve (closed without voltage) – in the idle state without current, it is closed, and opens when voltage is applied. This is the configuration used for the safety shut-off of gas, as it guarantees that in the event of a power failure or an alarm (when the electronics disconnect the power), the gas will automatically close.
- NO valve (open without voltage) – in the idle state it is open and closes when voltage is applied. It is rarely used for safety gas leak detection, as in the event of a power failure, the gas would continue to flow freely.
When ordering a separate valve outside of a pre-prepared set, this is one of the most important parameters to verify – a substitution with the NO variant is one of the most serious mistakes that can be made during the installation of a safety system, as it appears to be a fully functional system (during testing, the valve "does something" during an alarm), but in reality, it does not perform its protective function in the event of a power outage. With complete sets, such as the AVANSA 100M range with a solenoid valve, this compatibility is already resolved at the factory and there is no need to check anything further.
Wiring diagram of the detector and solenoid valve
A typical installation consists of a detection unit (sensor + evaluation electronics), a power supply, a solenoid valve installed on the main gas supply before the first branch to the appliances, and optionally an alarm siren or beacon. Below is a simplified diagram of a typical installation in a boiler room or kitchen of a commercial establishment.
The valve is physically installed on the pipe with a sufficient straight section before and after the valve (a minimum of 5x DN before and 3x DN after the valve is recommended if required by the manufacturer), in an accessible location for possible servicing, and always in the direction indicated by the arrow on the body of the valve. A detailed installation procedure including electrical connection to the terminal block of the control unit is discussed in the separate article "Installation and wiring of a gas detector with a solenoid valve."
Other parameters often overlooked in practice
Type of gas and sealing material
A valve designed for natural gas and a valve designed for propane-butane may look similar in construction, but they differ in the material of the sealing elements (NBR for natural gas, or FKM for higher resistance to LPG). When ordering, it is always necessary to specify for which medium the valve will be used – the differences between natural gas and propane-butane are discussed in detail in the article "Natural gas detector vs. propane-butane detector: what difference it makes and what it means for selection." Since propane-butane is heavier than air and accumulates at ground level, while natural gas rises to the ceiling, not only the location of the detector differs, but also indirectly the pipe routing and thus the location of the valve installation.
Operating voltage of the coil
Solenoid valves are supplied with a coil rated for 230 V AC or 24 V DC/AC. In complete sets with a detector (e.g., AVANSA 100M with a valve), the coil voltage is already matched to the output of the control unit, so no calculations are needed. When combining a separate detector (e.g., Gas detector AVANSA 100M or Detector AVANSA 150MC) with a separately purchased valve, it is necessary to verify whether the relay/output of the detector can handle the switching current of the valve coil (typically 0.3 – 0.8 A for smaller DN sizes), or to use an auxiliary contact relay for larger G1" valves with higher current draw.
Rated pressure PN and maximum operating pressure
Common gas solenoid valves for domestic and commercial use are dimensioned for low-pressure distribution (up to 0.5 bar), which covers the majority of residential and commercial installations in Slovakia. In industrial applications with medium-pressure distribution, it is necessary to verify whether the specific valve model is suitable for the given pressure range – these are typically more specialized projects outside the standard range for home use.
Step-by-step process for selecting the correct valve
In practice, this process means: first, you calculate the rated powers of all gas appliances that will be behind the given valve (boiler, stove, flow heater), determine whether it is a low-pressure domestic supply or a medium-pressure connection, check what thread the existing pipe has at the planned installation location, choose the appropriate size (G1/2", G3/4" or G1") based on the power and tabular Kv values, and finally verify whether the selected model is of type NC, what voltage the coil requires, and in what environment (humidity, dust) it will be installed, so that it corresponds to the IP rating.
Comparison of flow capacities of individual valve sizes
This graph is for quick orientation only – the exact Kv coefficient of a specific valve model is always listed in the technical datasheet, from which a designer or experienced plumber can accurately calculate the pressure loss for a given pipe configuration. At boundary performance values (e.g., 45-55 kW), it is recommended in practice to choose a larger size, as extra flow capacity does no harm, while an undersized valve causes real operational problems.
When to choose a complete set and when to combine components separately
For most standard installations in single-family homes, apartments, small businesses, and boiler rooms, we clearly recommend complete sets of detector + solenoid valve, where compatibility (voltage, NC type, switching output) is already solved by the manufacturer, saving the plumber time and reducing the risk of error. Atria.sk offers three such combinations based on the proven AVANSA 100M detector:
- AVANSA 100M + solenoid valve G1/2" DN15 – apartment boilers, single-family homes
- AVANSA 100M + solenoid valve G3/4" DN20 – larger homes, small businesses, restaurant kitchens
- AVANSA 100M + solenoid valve G1" DN25 – boiler rooms in apartment buildings, industrial facilities
We choose a separate combination (e.g., detector AVANSA 150MC with an external valve from another manufacturer) mainly when a valve with suitable parameters is already installed in the building (e.g., from a previous renovation) and it only needs to be properly connected to the new detector, or when the project requires a specific pressure range not covered by the standard set. Differences between individual AVANSA detector models are discussed in detail in the article AVANSA 100M vs AVANSA 150MC vs AVANSA 200M: comparison and recommended use.
Most common mistakes in valve selection and installation in practice
Over the years of supplying and servicing gas detection systems, we repeatedly encounter several typical errors:
- Selecting by thread size without calculating the output – described above, leads to pressure losses or unnecessary overdimensioning.
- Mixing NC with NO valves when purchasing components from different manufacturers separately – the system may appear to function normally, but it does not fulfill the safety function in case of power failure.
- Mounting in the wrong flow direction – the valve has an arrow on its body indicating the flow direction; if mounted in the opposite direction, it either does not seal properly or does not fulfill the sealing function at all when closed.
- Insufficient straight pipe section before the valve – causes turbulence and reduces the lifespan of the sealing.
- Placing the valve in an unsuitable environment without considering the IP rating – a coil exposed to moisture or condensation without appropriate protection can corrode and fail over time.
- Forgetting that after a power failure, the valve must be manually "pulled" again or the system must be restarted – for some types, a manual reset on the control unit is required after closing, not automatic reopening, which is the correct safety behavior, but the operator must be prepared and trained for this.
Common faults and causes of false alarms, which can also be indirectly related to valve cycling, are discussed in the article Common faults and false alarms of gas detectors. We also recommend not underestimating regular functionality checks – the topic is covered in the article Maintenance, calibration, and sensor lifespan of gas detectors.
Valve placement in relation to detector placement
The solenoid valve is not installed at the detector location, but on the main gas supply line to the protected area – most commonly right after the main gas shut-off valve or after the gas meter, before the first branching to individual appliances. On the contrary, the detector is placed according to the type of gas (natural gas rises, so it is mounted closer to the ceiling; propane-butane sinks, so it is mounted closer to the floor) – detailed instructions on height and placement can be found in the article Detector placement and mounting height according to gas type. The cable between the detector and the valve (or between the detector, control unit, and valve, if these are separate components) must be routed in such a way that it is not exposed to mechanical damage, and the length of the run should not exceed the values recommended by the manufacturer due to voltage drop on the coil.
Frequently asked questions about selecting a solenoid valve
Can I purchase a valve from another manufacturer for the AVANSA 100M detector?
Yes, provided the valve matches the electrical parameters of the detector's output (voltage, maximum switching current) and is of type NC (closed without power). However, it is simpler and safer in terms of warranty and functionality to choose a ready-made set, for example, AVANSA 100M with a solenoid valve in the required size.
What happens to the valve in case of a power outage in the house?
A properly selected safety (NC/fail-safe) valve automatically closes in case of power failure, just as it does during an alarm from the detector. This is the desired behavior, as the detection itself does not function without electricity, and the preventive closure of the gas supply is safer than leaving it open.
How can I determine which valve size I need if I don't have a gas installation project?
The easiest way is to calculate the total rated power of all gas appliances behind the valve installation point and compare it with the approximate values in the table above (up to about 40 kW for G1/2", up to about 80-90 kW for G3/4", and above that for G1"). For borderline values or more complex piping, we recommend consulting a gas installation designer or a gas equipment inspection technician.
Must the valve be manually reset after closing, or does it open automatically?
Most safety systems are designed so that after an alarm and valve closure, a manual reset on the detector control unit is required after the space has been ventilated and the cause of the leak has been removed. Automatic reopening without operator intervention is deliberately not used in safety applications.
Can one solenoid valve be used simultaneously for natural gas and propane-butane?
Mechanically yes, if the seals are made of a material suitable for both media (e.g., FKM), but in practice, the valve is always ordered and certified for the specific type of gas stated in the project. Therefore, when changing the fuel type in the building, the valve parameters must be re-verified.
Is there a difference between a valve for a household and one for an industrial boiler room?
Yes, besides the size, they also differ in the nominal pressure PN for which the valve is certified, the robustness of the construction, and sometimes also in the requirements for additional position signaling (limit switches) for connection to the boiler room's higher-level control system.
Conclusion
A solenoid valve is not just a "piece of metal with a thread" that you buy depending on the pipe thread – it is a functional safety component of the entire detection system, which must correspond to the actual gas flow, the type of medium, the electrical parameters of the detector, and must be designed as fail-safe (NC). For standard installations in households and smaller facilities, the simplest and most reliable solution is to use a verified combination of detector and valve in one set, where the manufacturer guarantees mutual compatibility – for example, AVANSA 100M with a G1/2" valve for apartment boilers, with a G3/4" valve for medium-sized facilities or with a G1" valve for larger boiler rooms. A complete overview of detectors and related solutions can be found in the Detectors category, where we are happy to advise you individually on the specific combination according to the parameters of your particular installation.
Do you have a question on this topic?
Are you unsure or dealing with a specific situation in your home? Write to us – we are happy to help.