How is the pre-charge pressure of a diaphragm expansion vessel tested?

The gas pre-charge pressure (p0) must be measured when the vessel is completely depressurized on the water side. To do this, isolate the vessel using the cap valve, drain the water inside the vessel completely via the drain valve, and then measure the gas pressure at the valve. If it deviates from the target value, it must be adjusted with nitrogen.

What information must be included in an inspection protocol for pressure maintenance systems?

A complete protocol must include the system data (static height, safety valve response pressure), the characteristics of the vessel (manufacturer, type, nominal volume), the determined target and actual values (gas pre-charge pressure, filling pressure, operating pressure), and the test status of the cap valve, safety valve, and any existing water make-up stations.

Why must target and actual pressures be documented in detail?

Complete documentation serves as proof of proper maintenance in accordance with DIN EN 12828 and VDI 4708. It enables the specialist company to identify gradual pressure losses immediately during subsequent inspections and serves as important evidence for insurance companies and manufacturers in the event of damage.

What is additionally inspected on an active, controlled pressure maintenance station?

For active systems (pump- or compressor-controlled), the electrical connections, the function of the control unit, the activation of the solenoid valves, the runtimes and error messages of the pumps or compressors, and the correct function of the level measurement in the pressureless vessel are also checked.

SHK & Heizung7

Expansion Vessel & Pressure Maintenance Protocol

Name: ProtocolHero
Brand: ProtocolHero

Proper pressure maintenance is the foundation of any efficient heating and cooling system. With our digital inspection protocol for expansion vessels and pressure maintenance stations, service technicians can quickly, systematically, and paperlessly document all target and actual values directly on-site.

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Preview of the “Expansion Vessel & Pressure Maintenance Protocol” template

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Short answer

What is the “Expansion Vessel & Pressure Maintenance Protocol” template for?

Inspection protocol for expansion vessels & pressure maintenance systems. Digitally document according to DIN EN 12828. Try it now with ProtocolHero!

Use case: SHK & Heizung
Captured data: General data on the property, order, heating system, and plant room, System-specific parameters such as static height and maximum allowable pressures, Recording of individual diaphragm expansion vessels (MAG) or active pressure maintenance stations
Result: A structured form that can be completed directly in the browser and reused in ProtocolHero.

Check the template against the technical, contractual and legal requirements of the specific case. ProtocolHero does not replace professional assessment.

Inhalt der Vorlage

What is included in the protocol template?

General data on the property, order, heating system, and plant room

System-specific parameters such as static height and maximum allowable pressures

Recording of individual diaphragm expansion vessels (MAG) or active pressure maintenance stations

Precise comparison of target and actual values for pre-charge, filling, and operating pressure

Condition check of the diaphragm, gas valve, cap valve, and shut-offs

Functional testing of pressure gauges, safety valves, water make-up, and degassing systems

Defect recording with photo documentation, actions, deadlines, and digital signature

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Use the Pressure Maintenance Protocol Digitally

Use this template in ProtocolHero and adapt it flexibly to the local conditions and manufacturer specifications.

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Why regular testing of pressure maintenance is essential

Inadequate pressure maintenance inevitably leads to air pockets, circulation problems, and increased wear due to corrosion in heating and cooling systems. Only when the expansion volume of the system can be correctly absorbed at all times will the entire system run energy-efficiently and safely.

Regular inspection ensures that no impermissible vacuum occurs, which would draw air into the system, and simultaneously prevents an excessive pressure increase that would trigger the safety valve.

Prevention of cavitation damage to circulation pumps
Protection against oxygen ingress and resulting system corrosion
Ensuring optimal heat transfer throughout the building

Preparation and determination of system-specific target values

Before taking the actual measurements, the specific parameters of the heating system must be recorded. These primarily include the static height of the system and the response pressure of the installed safety valve.

These values form the mathematical basis for the optimal gas pre-charge pressure and the required minimum operating pressure. Guidance is provided by the technical rules of DIN EN 12828 and VDI 4708 Part 1.

Determination of the static height starting from the center of the expansion vessel
Determination of the safety valve response pressure (psv)
Comparison with the manufacturer-specific design data of the pressure maintenance system

Pre-charge pressure test in a water-side depressurized state

A common mistake in practice is measuring the gas pre-charge pressure while the vessel is under water pressure. For an accurate measurement result, the diaphragm expansion vessel (MAG) must be completely depressurized on the water side.

This is done by closing the lockable cap valve and then completely draining the vessel via the drain valve. Only in this state may the gas pre-charge pressure be measured and, if necessary, adjusted with nitrogen.

Isolating and securing the cap valve against accidental closing
Complete draining of the water from the expansion vessel
Measurement and documentation of the gas pre-charge pressure (Target/Actual)

Safety functions, defects, and digital completion

In addition to the pure pressure values, a professional inspection also covers the auxiliary components of the pressure maintenance system. These include automatic water make-up stations including backflow preventers as well as degassing systems.

Any detected defects, such as a defective diaphragm or a leaking gas valve, are documented directly in the protocol with photos and assigned a rectification deadline. The report is finally signed digitally on a tablet or smartphone by the technician and the operator.

Functional testing of the water make-up and degassing equipment
Visual inspection for corrosion and leaks at all connections
Legally secure archiving and direct PDF dispatch to the customer

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