Oil pan stress tests v4.3


In mid-February, we wrote about the progress in the development of our oil cooling system, specifically the latest v4.3 oil bath, which has become a prototype for live testing. Many of you were mainly interested in the technical changes compared to the original version. For example, where did the ribbing go 🙂

The oil pan v4.3 has already been completed in our dedicated production hall. As we have written, the design had to be modified in the end due to the available materials and technologies used. The van can only accommodate two HPE Moonshot server cabinets (90 servers in total) instead of the original four (180 servers in total).

In order to use four, we would have to have the bathtub custom made somewhere abroad using other technologies and have a special sheet metal made. It would also be necessary to reinforce the structure, which would significantly increase the price and weight.

For us, on the other hand, smaller baths are not a problem. From an operational point of view, this is not a complication and there will be advantages in spreading the risks.

The prototype is already in DC2

The prototype of the oil bath, where the oil cooling tests will run, is already on the shelf in our second datacentre and these are the first quick photos…

The tub is made of stainless steel, the walls are triple-walled (there are 2 separate and independent cooling circuits). Higher safety, higher reliability.

It doesn’t look that big in the photo, so we’ll add two more colleagues to give you an idea.

There are grommets on the back for the wiring. These must have several important properties, including resistance to oil buildup.

So there will be oil in the tub and servers swimming in the oil. Soon.

Thanks to the new cooling concept, there will be no need for fins to cool the oil with water. Both cooling circuits have an inlet and outlet at the bottom of the tub. The two cooling circuits are there for redundancy and greater fault tolerance. We could have merged the two circuits into one, but we opted for a more challenging solution that will bring several additional benefits in the future.

Stress testing

We went to see the new tubs on Monday, which coincidentally was the first of April. So we thought we would take advantage of the situation and do stress tests.

As it turns out, oil baths are very spacious and even comfortable from the inside.

So if the oil cooling project fails we can use them for other purposes. For example, as a solarium, hybernation chamber or for an anonymous nail studio 🙂

Just for the record. The load capacity of one rack, which is for 12 similar tubs, is 8,520 kg. Each tub can weigh up to 710 kg. In each oil bath will be 2x fully equipped HPE Moonshot, which weighs up to 90 kg. In our case, it will be less because we will not use the lid and fans. So all in all, we’ll be using just under 170 kg. There are also about 230 litres of oil (just under 200 kg) and just under 85 litres of coolant (water in our case). The stainless steel tub weighs approximately 152 kg.


We like the tub and the first stress tests were successful. Now we need to put the server cabinets in them and start the test run. We’ll see soon.