Expansion systems

Expansion systems

Expansion units with compressor


The entirely micro-processor driven control unit in the MKU / MKS expansion vessel has a number of parameters that can be set to any variable within a given range. Other characteristics of the MKU / MKS are the high level of reliability and sturdiness.

The MKU / MKS is adaptable to a wide range of situations and there are plenty of optional accessories which mean that it can be put to many different uses in countless systems. It requires no oil or maintenance. The MKU / MKS compressor expansion vessels store the expansion water from the system. They also hold the system pressure at the pre-set level within clearly defined limits. Water and compressed air are separated from each other by a removable high-quality butyl-rubber membrane which has a high diffusion density (low gas permeability). Produced in accordance with the Pressure Equipment Directive 2014/68/EU and the Machinery Directive 2006/42/EC.


The SOTEX MK add-on vessels for the simply enlargement of the expansion capacity are not equipped with a controller or compressor. The vessel to be connected must be similar to the basic vessel and connected on the air side by means of a pressure hose. Quick-release couplings are provided.

The MK coupling vessels take up the expansion water of the installation. Water and compressed air are separated from each other by a removable high-quality butyl-rubber membrane which has a high diffusion density (low gas permeability). Produced in accordance with the Pressure Equipment Directive 2014/68/EU and the Machinery Directive 2006/42/EC.

Expansion systems with pump

EcoFlex PLE

The SOTEX EcoFlex PLE expansion vessel is a particularly investment-friendly expansion system ideal for export projects.

The EcoFlex PLE is an expansion system equipped with a pump and an EPDM membrane. The membrane ensures that water and air are kept separate; it is mounted horizontally to the top of the vessel and it ‘drives’ continuously to the water level. The vessel has an extremely long service life because it operates in a pressureless state. Also available with special supply voltages and special dimensions.

EcoFlex PLV

The SOTEX EcoFlex PLV add-on vessels make it easy to increase the expansion volume without having to add an extra control unit directly.

However, it is possible that the pump capacity of the vessel will have to be adjusted. For more advice about the options available, please contact our sales department.

EcoFlex PLC

The SOTEX EcoFlex PLC expansion set is a combination of an PLE expansion vessel and one or more PLV add-on vessels.

Membrane expansion vessels

Membrane expansion vessels

The membrane expansion vessels are particularly suitable for use in central heating and cooling systems according to EN12828. They more than comply with the European directives, and are provided with the CE mark. The SOTEX product range offers (fixed) membrane expansion vessels with a capacity of 100 to 1,000 litres, available in two pressure classes, 6 and 10 bar.

Membrane expansion vessels type M

The ‘M’ type with exchangeable butyl rubber membrane offers you extra-special advantages in installations with big differences between the static pressure and set pressure of the safety valve. The sophisticated design delivers high efficiency, which means that the capacity of the vessel is used to best effect.

Auxiliary expansion vessels (cooling vessels)


Intermediate vessels are designed to cool down the expansion water before it enters the expansion vessel or expansion units. A control vessel is necessary if the expansion water has a temperature higher than 70°C. Available from 200 to 2,000 litres, pressure class 6 or 10 bar.

Nitrogen Expansion systems

Nitromat Pro VP

The Sotex Nitromat Pro VP nitrogen expansion system generally consists of a Nitromat Pro nitrogen generator, a compressor and a nitrogen storage vessel. With a SOTEX nitrogen expansion system you are always assured of pure nitrogen to protect your vertical heat / cold storage tank.

The Nitromat VP series are highly reliable nitrogen generators, energy efficient and deliver a purity of 99% nitrogen or more. The Nitromat VP is the standard version in the product range and comes with highly reliable components from global brands, effective compressed air treatment, oil/water separator and a Siemens PLC control. The SOTEX Nitromat VP nitrogen generators are built according to the European CE PED directive, executed according to UL/CSA directive and have an EAC CU TR certificate. The SOTEX VP nitrogen system is applied to vertical storage tanks, where the standard version can provide one tank with a nitrogen blanket (pressure in mbar).

An intelligent and user-friendly Siemens control regulates the pressure balance of the nitrogen cushion in the heat storage tank and monitors the water content. This way you can rely on optimal security and protection of the tank and heating system.
The SOTEX nitrogen expansion systems successfully protect precious heat storage tanks all over the world. There are also SOTEX nitrogen expansion systems for the use on horizontal heat storage tanks using special buffer vessels for the expansion collection and of course the SOTEX nitrogen systems are used very successfully in more and more Geothermal projects. Communication modules such as Modbus, Profinet and Profibus and / or an extranet and internet are optional.

The new SOTEX Nitromat Pro nitrogen generators provide you with desired information such as the pressure in the buffer tank, content in percent and centimeters and also the pressure in the nitrogen storage vessel, all clearly displayed on a 7 ″ multi-colored touchscreen. Of course we can offer the desired information for application to your system, such as communication modules such as Modbus, Profinet and Profibus. Connection to an extranet and internet are of course also possible.

The most unique thing about the Nitromat Pro is the “Easy Commissioning” help. As soon as you start up the installation for the first time, you will be guided step-by-step through the large screen during commissioning by means of clear instructions, questions and sample photos.

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Nitromat Pro HP

The Nitromat Pro HP is the same as the VP series but work with a working pressure of 1 up to 2 bar (optional to change) so there is a pressure holding system. These nitrogen expansion vessels are usually applied to PED approved buffer tanks, which are used as expansion vessels. For example, in systems with high medium temperatures (> 120 ⁰C) this is an ideal system compared to regular expansion vessels.

Accessories for Nitrogen Expansion systems

Supplied as standard:

Optionally included:

Sotex: Expansion systems