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The Graebener stack press supports the technical testing of electrolysis stacks at the end of their production process: The pre-assembled stack, which consists of a large number of plates, is first moved into the machine and then compressed to a defined height until a certain pressure is reached within the stack. This pressure must then be maintained unchanged for several hours. At this time, the stack is subjected to all the necessary technical tests carried out by the customer and with the help of further procedures. These are necessary to confirm its full operability. As soon as the tests are completed, the stack is finally assembled with tie rods or tension straps and the finished stack is removed.

The stack press for electrolyzers has a force of 800 tons and can handle stacks with a maximum height of approx. 3.0 m, a maximum diameter of 1.60 m and a weight of up to 12 tons per stack.

In order to be able to guarantee assembly work during operation with maximum safety, a hydraulic drive was deliberately avoided. Instead, the stack is compressed inside the press by means of six servomotor-driven spindle units. These are operated synchronously and thus enable particularly homogeneous compression of the stack. The maximum pressing force per spindle unit is 150 tons.


Electrolyzers make a significant contribution to the energy transition because they can be used to convert electricity, preferably from renewable sources, into hydrogen. This, in turn, can be used in a variety of ways as a green energy source, for example to decarbonize the industry. The heart of every electrolyzer is its stack, which consists of hundreds of stacked single or bipolar plates. The chemical conversion of electrical energy into hydrogen then takes place within these stacks.

Future outlook

To achieve the political goals of becoming climate-neutral, we will need huge amounts of renewable energy in the future, including green electricity and green hydrogen. Decarbonizing industry is an important lever on the way to climate neutrality. Green hydrogen will play a key role in many sectors of industry (e.g. steel and fertilizer production).