Опрессовку проводят, с тем чтобы проверить циркуляцию теплоносителя.

Because опрессовка is a feminine noun, and here it is the direct object of проводят.

• Nominative: опрессовка
• Accusative: опрессовку

Russian asks, in effect, conduct what? → опрессовку.

So the ending changes because the noun is in the accusative singular.

This is a very common Russian pattern. The verb in the 3rd person plural can be used with an indefinite or generic subject:

• проводят = they carry out / people carry out / one carries out

In technical or formal writing, this often corresponds to English passive wording:

• Опрессовку проводят...
• literally: They carry out pressure testing...
• natural English: Pressure testing is carried out...

So Russian often uses an active plural verb where English might prefer a passive.

Yes. In this context, проводить means to carry out, perform, conduct.

It is a very common verb with procedures, tests, inspections, experiments, and similar actions:

• проводить проверку = carry out an inspection/check
• проводить испытание = conduct a test
• проводить опрессовку = carry out pressure testing

Here it is the imperfective verb проводить, which fits well because the sentence describes a standard procedure or general practice, not one single completed event.

С тем чтобы is a formal way to express purpose. It means:

• in order to
• so as to
• with the aim of

So:

• Опрессовку проводят, с тем чтобы проверить...
• Pressure testing is carried out in order to check...

This expression is more formal and bookish than plain чтобы. In many everyday contexts, Russian would simply use чтобы.

Because с тем чтобы проверить циркуляцию теплоносителя functions as a purpose clause attached to the main clause.

Russian normally separates this kind of clause with a comma, especially in formal written style:

• Опрессовку проводят, с тем чтобы проверить...

If you replaced с тем чтобы with чтобы, you would also normally keep the comma:

• Опрессовку проводят, чтобы проверить...

So the comma is standard punctuation here.

Because проверить is perfective, and after a purpose expression it often emphasizes the intended result: to complete the check, to verify successfully.

Compare:

• проверить = to check/verify completely, to get the result
• проверять = to be checking, to check repeatedly or as a process

After с тем чтобы, the perfective infinitive is very natural when the goal is a finished outcome:

• ...с тем чтобы проверить циркуляцию...
• ...in order to verify the circulation...

So the idea is not just to engage in checking, but to determine whether the circulation is functioning properly.

This is a very common Russian noun pattern.

1. циркуляцию is accusative because it is the direct object of проверить:

   • проверить что? → циркуляцию

2. теплоносителя is genitive because it depends on циркуляция:

   • циркуляция чего? → теплоносителя
   • literally: circulation of the heat-transfer fluid

So the structure is:

• проверить
  • циркуляцию
• циркуляция
  • теплоносителя

This is similar to English the circulation of the coolant.

Grammatically, теплоноситель is a masculine noun.

Its role here is:

• base form: теплоноситель
• genitive singular: теплоносителя

It appears in the genitive because it depends on циркуляция:

• циркуляция теплоносителя = circulation of the heat-transfer medium / coolant

Even if you already know the meaning, the important grammar point is that Russian often uses the genitive for this kind of X of Y relationship.

Yes. A simpler and less formal version would be:

• Опрессовку проводят, чтобы проверить циркуляцию теплоносителя.

This means essentially the same thing, but чтобы is more straightforward and common than с тем чтобы.

The original sentence sounds more formal, technical, and written. That is typical for engineering or procedural language.

The word order is natural for formal technical Russian.

• Опрессовку проводят — first states the procedure being carried out
• с тем чтобы проверить... — then states the purpose

Russian word order is flexible, but this order is good for technical prose because it presents:

1. the action/procedure
2. the purpose

You could rearrange it, but the original sounds appropriately formal and standard.