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Why monitor compressed air?

Leaks waste energy and money
At a time of increasingly rising energy costs, it is even more important to exploit potential savings in order to remain competitive. Many users of compressed air have no idea how high the total consumption of compressed air is and hence are unaware of the extent of the cost of leaks.

The efficiency of a compressed air supply system begins with the generation of compressed air and ends with the consumer. Loss of compressed air through leaks in the pipe network generates extremely high costs and reduces efficiency. Until now these costs were hidden in the overall electricity bill and were not transparent. Complete transparency usually prevails in all companies with regard to the consumption of most other mediums such as electricity, water and gas. Water meters, for example, indicate the exact water consumption. In contrast to compressed air, water leaks are immediately visible to everyone and are repaired straight away whilst air continues to escape unnoticed from leaks in the compressed air network even at the weekend and during shutdowns. The compressors continue to turn blithely during this period just to maintain constant pressure in the network. These observations do not cover the cost of “generating clean, dry“ compressed air. Refrigeration driers and adsorption driers dry the air at considerable running costs, for it then to be just carelessly wasted.

This chart indicates the costs and energy loss associated with leaks. An undetected hole as small as 5mm can cost a plant €16,176 per year. Leaks are only audible when larger than 1mm² at a pressure of 7 bar. Predictive leak detection and repair will result in substantial cost savings and system efficiency.

Hole Diameter Air Leakage Euro lost
1mm 1,8 l/s € 480/year
3mm 20,8 l/s € 6.096/year
5mm 58.5 l/s € 16.176/year
10mm 235,2 l/s € 63.360/year

How are the leaks detected?
Our sensors monitor air consumption to detect leakage areas in two ways
Method 1: when machine is in operation the sensor compares the machine’s ideal air consumption to the actual air consumption. The difference indicates an air leakage.
Method 2: when machine is shutdown the sensor continuously monitors the machine during shutdown. Any air consumption that is measured indicates an air leakage.

Our sensor can also monitor

Leakage per individual machine
Leakage per zones in a plant
Consumption per machine cycle
Consumption per shift
Consumption per zones in a plant

Verification of leak repair and system improvements
Dividing a plant into zones is key to leak detection
In order for the sensor to provide predictive maintenance information, a plant should be first divided into zones based on the number of fittings and potential leakage points. After sectioning a plant into smaller, more manageable zones, the sensor is mounted in the supply line to the zone. The sensor will detect leakage areas based on the zone’s increase in air consumption over time or monitor air consumption when machines in the zone are shut down.

After a leakage area is detected, leak repair can occur quickly.
The sensor will target a leakage area by zone so that plant personnel can focus on a specific, smaller area, rather than search an entire plant for air leaks. With the zone identified, maintenance can quickly pinpoint the exact leak location and repair the leak. The best method for this is to use an ultrasonic acoustic detector and follow up with soap and water applied to the suspected leak.

A predictive maintenance sensor

The Zefair series give you a compact compressed air consumption measurement unit with display and totalizer function. A valuable aid to detect leakage areas.

Integrated 4-digit numeric display
The compact monitor features a 4-digit numeric LED display that provides air consumption readings. Microprocessor-based pushbutton programming provides easy set-up. Two display options

  • Nl/min (normal liters/min)
  • Nm3 /h (normal cubic meters/hour)

Four sensor options available

  • DN15 pipe connection, 0,25…75 M3/h measuring range
  • DN25 pipe connection, 0,75…225 M3/h measuring range
  • DN40 pipe connection, 0,75…410 M3/h measuring range
  • DN50 pipe connection, 0,75…700 M3/h measuring range

Micro DC connector
24 VDC unit provides power connection and outputs.

  • Switching output
  • Pulse output
  • Analogue output (4-20 mA)

Integrated pipe length
Ensures easy mounting and proper mounting depth.

The technology behind the Zefair sensor is based on the calorimetric flow sensing principle.

Zefair incorporates two ceramic flow sensing elements that each contain a thermistor.
As one sensor element is heated, the second element is used as a reference. Power is then altered to the heaters to ensure a constant temperature difference
(CTD) between the two elements.

The CTD method allows for greater sensitivity in air consumption, a faster response time, and a wide sensing range. Its acute sensitivity can detect extremely small leaks, yet at the same time, measure the air consumption of high-capacity compressed air systems.

With the compressed air consumption meter, we provide the user with a low-cost opportunity to precisely measure the current compressed air consumption as well as the total consumption. To do so, the sensor is mounted and adjusted in a pipe length at the factory.

Due to the high sensitivity even minute quantities, like those that for example occur in case of leakage, are detected at an early stage and can be repaired.


Humidity control: How to prevent damage

The modern production technology needs compressed air. The diversity of application starts with non processed blast air to absolute dry, oil-free and sterile compressed air. Irrespective of how it is used, compressed air has to be dry. Depending on the application considerable economical damage can be caused by uncontrolled „humidity irruption“ into the compressed air system.

Reasons that can lead to an increased pressure dewpoint value within the compressed air system

Condensate at the refrigeration dryer (condensate eliminator faulty or dirty)
Condensate overload of the refrigeration dryer
Adsorption agent is not regenerated sufficiently
Compressed air bypass in the bypass (valve faulty or not closed)
Compressed air bypass in the refrigeration dryer (worn out, corroded etc.)

Water in compressed air leads to damages

Corrosion within the pneumatic plant -Rust will develop in the ducts and functioning elements and will lead to leakages.
Breakage of the lubricating film – Broken lubricating films lead to mechanical faults.
Building of electric elements.
Formation of ice in the compressed air system - At low temperatures the water within the compressed air system could freeze and cause frost damage, reduction of the diameter and blockades.
Material handling - High humidity leads to conglutination of materials to be transported, e. g. sugar, concrete, granulate, etc.
Pharmaceutical -High humidity impairs powders, tablets, etc.
Hospital - DIN 13260, EN 737-3, danger of development of bacteria

What is pressure dewpoint and how it affects air quality?
Dew point measuring is an effective way of determining the amount of vapour contained in a gas. It is the specific temperature, at a given pressure, under which vapour condensates to water. Increasing the pressure of a gas also increases its dewpoint temperature.

According to Dalton’s law, in any mixture of gases, the sum of the partial pressures of the component gases equals to the total pressure of the mixture. When compressing ambient air, the non neglectable amount of vapour it contains also increases its partial pressure. Given the fact that there is a specific pressure threshold for vapour, in a unique correlation to temperature, above which it becomes saturated (in other words its dew point becomes equal to the given temperature), dew point (also called pressure dew point for compressed gases) is a direct indicator of vapour saturation in a compressed air system. Therefore, measuring pressure dew point of air in a compressed air system can help us monitor the performance of the dryer and water-traps used and warn us before vapour starts saturating and becomes harmful both for equipment and users.

Sigma offers a complete range of sensors and instruments for monitoring dewpoint, temperature and humidity that can easily fulfil your specific needs.


Having an oil free compressor does not necessarily mean that your compressed air is oil free as the term “oil-free compressor” refers only to the compression chamber, not the compressor system as a whole, or the resulting compressed air quality.

Contaminants in the compressed air system generally can be attributed to:
The quality of the air drawn into the compressor
The operation of the air compressor
Compressed air storage devices and distribution systems

Many industrial processes are very sensitive to oil contamination, but up to now the only method for measuring the in-pipe oil content involved specialist equipment and a time-consuming laboratory analysis.

What we offer is a unique high technology on-line solution.

Using a sophisticated measurement technology based on ion exchange, the oil monitoring and control system provides the user with continuous on-line readings of the actual oil content at any given measurement point within the user’s compressed air system.

The product has two parts: the sensor unit for vertical installation into the pipe, and a display unit. The display unit offers user-definable alarm limits, and as the measured oil-level increases, so the display reading changes from standard green, through to warning yellow, and finally to flashing red to indicate that the user’s alarm levels are being exceeded. The unit also connects to a building management system for remote monitoring.