Skakel die espressomasjien af ingeval die stoomklep lek.

Because the basic verb is afskakel, a separable verb meaning switch off / turn off.

In a command or other main-clause pattern, Afrikaans often splits this kind of verb:

• Skakel die espressomasjien af.
• Ek skakel die espressomasjien af.

So skakel ... af works as one unit in meaning, even though the two parts are written apart here.

Yes. This is the imperative form, so it is a direct command or instruction: Switch off ...

In Afrikaans, commands usually leave out the subject:

• Skakel die lig af. = Switch off the light.
• Wag hier. = Wait here.

You can add jy or julle for emphasis, but normally you do not.

Yes, but not in exactly the same structure.

The dictionary form is afskakel. In this sentence, because it is a command, it appears as skakel ... af.

You will often meet different forms such as:

• Ek wil die espressomasjien afskakel.
• Om die espressomasjien af te skakel
• Hy het die espressomasjien afgeskakel.

So learners should think of afskakel as the full verb, while recognizing that it often splits in everyday sentences.

Afrikaans very often writes compound nouns as a single word.

So:

• espresso + masjien → espressomasjien
• stoom + klep → stoomklep

English often writes these as two words, but Afrikaans usually joins them. The last part is the main noun:

• an espressomasjien is a kind of masjien
• a stoomklep is a kind of klep

Die is the definite article, meaning the.

So:

• die espressomasjien = the espresso machine
• die stoomklep = the steam valve

Here it refers to a specific machine and its valve, not just any machine or any valve. If Afrikaans wanted an indefinite meaning, it would use 'n:

• 'n espressomasjien = an espresso machine

Ingeval means if or in case, especially when you are talking about a precaution.

So in this sentence, it introduces the reason for the safety action:

• Skakel die espressomasjien af ingeval die stoomklep lek.
• Switch off the espresso machine in case the steam valve leaks.

It suggests: do this now as a protective measure, because that problem might happen.

Because here it is being used as a conjunction, and the standard form is ingeval.

A useful contrast is:

• ingeval = if / in case
  • clause
• in geval van = in case of
  • noun

For example:

• Ingeval dit reën, bly ons binne.
• In geval van brand, bel die brandweer.

So in your sentence, ingeval is correct because it is followed by a whole clause: die stoomklep lek.

Because ingeval introduces a subordinate clause.

In Afrikaans subordinate clauses, the verb typically comes at the end. In this short clause, that gives:

• die stoomklep = subject
• lek = verb at the end

So:

• ingeval die stoomklep lek

This is a very common Afrikaans pattern after words such as dat, omdat, as, terwyl, ingeval, and others.

Afrikaans verbs usually do not change form according to the subject in the present tense.

So you get:

• Ek lek
• Jy lek
• Die stoomklep lek
• Hulle lek

Unlike English, Afrikaans does not normally add an -s for he/she/it. That is why die stoomklep lek is correct.

In Afrikaans, the simple present can cover several meanings that English separates more clearly.

So lek here can naturally correspond to:

• leaks
• is leaking
• should leak

In this sentence, the most natural English sense is something like in case the steam valve leaks or should the steam valve leak.

Sometimes yes, but the nuance changes.

• as is the ordinary word for if
• ingeval often sounds more precautionary, like in case

Because this sentence is about taking preventive action, ingeval is especially suitable.

Compare:

• Skakel dit af as die stoomklep lek.
  More like: switch it off if the valve leaks.
• Skakel dit af ingeval die stoomklep lek.
  More like: switch it off in case the valve leaks.

So ingeval better matches the idea of a safety precaution.