Anstataŭ ke ŝi pumpas la aertubon, mi kontrolas la valvon.

Anstataŭ ke means instead of or rather than.

It introduces the action that is being contrasted with the main action. So the structure is:

Anstataŭ ke ŝi pumpas la aertubon = instead of her pumping the air tube
mi kontrolas la valvon = I check the valve

So the sentence sets up one action as the alternative, and then gives the action that actually happens.

Ke is used because the part after anstataŭ is a full clause, not just a single word or an infinitive.

After ke, we get:

• a subject: ŝi
• a finite verb: pumpas

So ke ŝi pumpas la aertubon is a complete clause.

Compare:

• Anstataŭ ke ŝi pumpas la aertubon, mi kontrolas la valvon.
  Here the alternative action has its own subject: ŝi.

• Anstataŭ pumpi la aertubon, mi kontrolas la valvon.
  Here pumpi is an infinitive, and the understood subject is usually the same as the main clause subject, so it sounds like I am the one not pumping.

That is why ke is useful here: it lets Esperanto clearly say that she is the one associated with the alternative action.

Pumpas is a finite verb in the present tense, while pumpi is the infinitive.

Because the clause has an explicit subject, ŝi, you normally need a finite verb:

• ŝi pumpas = she pumps
• not ŝi pumpi

So if you keep ŝi, you need something like pumpas or possibly pumpu, not pumpi.

If you wanted the infinitive pumpi, you would normally remove the subject:

• Anstataŭ pumpi la aertubon, mi kontrolas la valvon.

But that version usually implies that mi is the one who would have done the pumping.

Yes. Many learners notice this, and it is a good question.

After anstataŭ ke, some speakers use -u to show the action as an alternative, expected, or not-actually-chosen action:

• Anstataŭ ke ŝi pumpu la aertubon, mi kontrolas la valvon.

That can sound more idiomatic to many people.

The version with pumpas is still understandable. It presents the pumping more as a stated action in the present. The version with pumpu can feel a bit more like instead of her pumping... as an unrealized or replaced possibility.

So:

• pumpas = understandable factual contrast
• pumpu = often preferred for an alternative that is not the chosen action

The -n marks the direct object.

In this sentence:

• ŝi pumpas la aertubon → the air tube is what she pumps
• mi kontrolas la valvon → the valve is what I check

So both nouns get -n because they are the objects of the verbs.

This is one of the most important Esperanto endings:

• -o = noun
• -on = noun used as a direct object

Yes. Aertubo is a compound noun:

• aer- = air
• tub- = tube
• -o = noun ending

So aertubo literally means air tube.

Esperanto makes compounds very freely, and the main idea usually comes at the end. Here the thing is basically a kind of tube, specifically an air tube.

This is very normal Esperanto word-building.

Usually no. This is a common trap for English speakers.

Esperanto kontroli usually means:

• to check
• to inspect
• to examine

So mi kontrolas la valvon usually means I check the valve, not I control the valve.

If you want the English idea of control in the sense of directing or operating something, Esperanto often uses another verb depending on context, such as regi or mastrumi.

The comma separates the introductory subordinate clause from the main clause.

Structure:

• subordinate clause: Anstataŭ ke ŝi pumpas la aertubon
• main clause: mi kontrolas la valvon

When the subordinate clause comes first, a comma is very natural and common in Esperanto.

So the comma helps show where the first clause ends and the main statement begins.

La is the definite article, like English the.

So:

• la aertubon = the air tube
• la valvon = the valve

It suggests that these are specific, known things in the situation. For example, maybe both speakers already know which tube and which valve are being discussed.

Esperanto has:

• la = the
• no separate word for a/an

So if you just say valvo, that can mean a valve or simply valve depending on context.

Yes, to some extent.

Esperanto word order is more flexible than English because the -n ending marks the objects. So you could move parts around for emphasis.

For example, you could say:

Mi kontrolas la valvon, anstataŭ ke ŝi pumpas la aertubon.

That is still understandable.

But the original order is natural because it puts the contrast first:

• first the replaced or alternative action
• then the action that actually happens

So the original sentence sounds like it is highlighting the instead of... idea right away.