difference between axial and radial manometer in heating

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Manometers are an essential tool in heating systems for pressure monitoring, yet their technical operation and installation methods are often confused. The difference between axial and radial manometers is not only in aesthetics, but primarily in the mechanism of pressure transmission to the pointer and the installation options in narrow boiler room spaces.

Physical principle and measurement construction

The basis of every manometer is a Bourdon tube, which deforms under pressure and this deformation is transferred through a gear mechanism to the rotation of the pointer. In a radial manometer, the inlet is placed perpendicular to the dial, meaning the pressure acts on the end of the tube from the side and the force is directly transferred to the center of the mechanism. This construction is traditional and very robust, but it requires more space behind the boiler or on the pipe due to the outlet pointing away from the wall.

In contrast, an axial manometer has an inlet oriented parallel to the plane of the dial, so the pressure comes "from behind" and pushes on the inner part of the tube along the axis. This design allows the entire measuring element to be hidden behind the dial or close to the wall, achieving minimal thickness of the entire device. For professional installations where space is limited, this construction is often the only possible solution that does not restrict access to other components.

Mounting options and space requirements

The choice of manometer type is often dictated by the physical layout of the pipe and boiler. Radial models require free space in front of the boiler or on the side of the pipe, as their body protrudes from the mounting plane. If the boiler is installed close to the wall or in a narrow shaft, a radial manometer can interfere with other systems or complicate the maintenance of surrounding components.

Axial manometers are designed to have the thinnest possible body and to lie flush with the mounting surface. These models are ideal for situations where it is necessary to maintain a clean pipe profile or where space behind the boiler is limited. An example is installation on distributors or directly on the boiler body, where a radial variant would hit the wall. On our website you will find a wide selection of these models, for example axial manometer 0 - 10 bar, 63 mm, which is a standard for most heating systems due to its compact design.

Radial: Requires 30 to 40 mm of free space in front of the mounting surface.
Axial: Uses only 10 to 15 mm of depth, the body is in one plane with the connection.
Accessibility: Axial models do not obstruct the view of other valves and sensors.
Aesthetics: They appear less bulky and are more suitable for modern boiler rooms.

Accuracy and resistance to vibrations

The quality of measurement depends not only on the calibration class, but also on how the mechanism is protected from external influences. Radial manometers often have a longer switching lever and differently arranged gears, which can be less stable under strong vibrations if not sufficiently secured. On the other hand, axial manometers have a short and solid construction that is naturally more resistant to shocks and shaking, as the center of gravity is closer to the point of attachment.

In practice, we have observed that axial models combined with a screw closure last longer without loss of accuracy near pumps or gas boilers that generate vibrations. Therefore, the recommendation for professional installations is clear: if there is a high probability of vibrations or narrow spaces, choose an axial variant. For common domestic applications with low load, however, both types may be suitable, with radial ones often being cheaper due to simpler production.

Selection of range and combination with a thermometer

Besides the shape, it is crucial to set the measurement range correctly. For common home heating, a range of 0 – 6 bar is sufficient, while for industrial systems or heat networks, a range of 0 – 10 bar or more is required. An important aspect is also whether you need to measure temperature simultaneously with pressure. In this case, a thermomanometer is often chosen, which combines both functions into one device. An axial thermomanometer is very popular in this category, as it combines compactness with comprehensive system diagnostics.

One of our best-selling products in this area is axial thermomanometer 0°C - 120°C 0 - 6 bar, 63 mm. This model is ideal for monitoring the condition of water in the boiler, as it shows not only pressure but also the current temperature, which is critical for preventing boiling or freezing. The choice between a separate thermometer and a thermomanometer depends on your preferences and space availability; if you have space, separate sensors can be more accurate, but thermomanometers save one connection.

Common heating: A range of 0–6 bar is sufficient for most systems.
High pressure: For heat stations or long pipelines, use 0–10 bar.
Temperature control: Thermomanometers eliminate the need to install an additional sensor.
Diameter: The standard 63 mm provides good readability even in smaller boiler rooms.

Common installation and usage errors

Incorrect selection of the type of manometer often leads to damage to the device or its inability to be read. The most common mistake is the installation of a radial manometer in a space where there is insufficient distance from the wall, which causes the dial to be pressed and the pointer to be unable to move freely, or the glass to be damaged. Another problem is ignoring the orientation of the connection; if the manometer is mounted incorrectly, it can cause the sealing to loosen or the internal mechanism to be damaged by pressure surges.

It is also important to ensure proper insulation of the capillary in the case of remote measurement, or to use a pressure damper in high-pressure systems. For correct installation and positioning of the pressure gauge on the boiler, the rule applies that it must be placed in a visible location and in a horizontal position to prevent condensation from accumulating in the mechanism. After gas replacement in the boiler, it is necessary to check the pressure gauge after resetting the pressure to ensure it shows the correct value, which requires knowledge of the procedure how to adjust the pressure gauge after gas replacement in the boiler.

Maintenance, calibration and fault diagnosis

Pressure gauges are mechanical devices that require periodic accuracy checks. It is recommended to calibrate them at least once every two years, especially in industrial operations where safety is a priority. If the pressure gauge shows zero even though there is pressure in the system, it may be due to a clogged capillary, a damaged Bourdon tube, or a loss of elasticity in the mechanism. Common pressure gauge faults are also associated with corrosion of the connection or loosening of screws due to vibrations.

To maintain the reliability of the system, it is important to monitor the axial pressure gauge 0 - 6 bar, 63 mm and regularly check whether the needle returns to zero after pressure is released. If it does not, the device needs to be replaced. Maintenance and calibration of pressure gauges in professional heating systems include not only visual inspection, but also verification of accuracy using a reference pressure gauge. It is advisable to keep a spare model in stock to prevent heating from stopping in the event of a failure.

Calibration: Recommended interval of 24 months for domestic and 12 months for industrial systems.
Diagnosis: Zero at pressure indicates a blockage or internal damage.
Vibrations: Regular check of the connection tightening and sealing.
Cleaning: Cleaning the window and dial for better readability.

Connection orientation and direction of pressure impulse

A key technical difference is also the way pressure acts on the internal parts of the mechanism when the valve is suddenly opened.

Common questions

Why does the pressure gauge show zero even though there is pressure in the system?

This phenomenon is most often caused by a clogged capillary, a damaged Bourdon tube, or a loss of elasticity in the mechanism after a long time. It may also be due to a loose connection, through which pressure is leaking.

How to choose the correct range of the pressure gauge for the heating system?

For standard home heating, a range of 0–6 bar is sufficient, while for industrial systems or thermal networks, a range of 0–10 bar or more is required. The range should always be 20–30 % higher than the maximum operating pressure.

What is better, a pressure gauge with a thermometer or a separate thermometer?

Thermopressure gauges save space and one connection, which is advantageous in narrow boiler rooms. Separate thermometers can be more accurate and easier to replace if they break, but they require more space on the piping.

In conclusion, it can be said that the correct choice between an axial and a radial pressure gauge mainly depends on the spatial conditions and mechanical stability of your boiler room. Both solutions are technically advanced, but axial models offer an irreplaceable advantage in compactness and resistance to vibrations, making them the ideal choice for modern professional installations.

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