Pompa de aer protejează echilibrul biologic.

Because pompa is the definite form of pompă.

• pompă = a pump
• pompa = the pump

Romanian usually puts the definite article at the end of the noun instead of using a separate word like English the. So here pompa de aer means the air pump.

Literally, de aer means of air, but in this sentence it works like an English noun modifier and means air in air pump.

So:

• pompa de aer = the air pump

This is a very common Romanian pattern:

• mașină de spălat = washing machine
• sticlă de apă = bottle of water
• pompă de aer = air pump

So you should not translate it too mechanically as pump of air in normal English, even though that is the literal structure.

Because after de in this kind of phrase, the second noun usually stays indefinite.

Here, aer is not referring to some specific air; it is just identifying the type or function of the pump. So:

• pompa de aer = the air pump
• not pompa de aerul

Using aerul would suggest the air as a specific, already-known thing, which is not the idea here.

Protejează is the 3rd person singular present tense of a proteja = to protect.

It matches the subject pompa de aer, which is singular:

• eu protejez = I protect
• tu protejezi = you protect
• el/ea protejează = he/she/it protects

Since pompa is it, Romanian uses protejează.

Romanian often leaves out subject pronouns when they are not needed, so you do not need to say ea protejează here.

For the same reason as pompa: echilibrul is the definite form.

• echilibru = a balance
• echilibrul = the balance

The ending -ul is the definite article here.
So echilibrul biologic means the biological balance.

Also, echilibru is a neuter noun. In Romanian, neuter nouns behave like masculine in the singular and feminine in the plural, which is why the singular definite ending here is -ul.

Because in Romanian, adjectives normally come after the noun.

So the normal order is:

• echilibrul biologic = the biological balance

This is more neutral and standard than putting the adjective first.

Romanian can sometimes place an adjective before the noun, but that usually adds emphasis, style, or a more literary tone. In this sentence, the ordinary, natural order is noun + adjective.

Because when a noun is definite and the adjective comes after it, the article usually appears only on the noun, not on the adjective.

So:

• echilibrul biologic = the biological balance

That is the normal pattern.

If the adjective comes before the noun, Romanian can attach the article to the adjective instead:

• biologicul echilibru

But that sounds much less neutral here and is not the usual way to say it in this sentence.

Yes, but the original order is the most neutral and straightforward:

• Pompa de aer protejează echilibrul biologic.

This is a standard subject + verb + object sentence.

Romanian does allow other word orders for emphasis, contrast, or style, but they would change the focus. For example:

• Echilibrul biologic este protejat de pompa de aer.
  = The biological balance is protected by the air pump.

That is grammatically fine, but it is a different structure and emphasis. For a basic statement, the original version is the most natural.

A few useful pronunciation points:

• ă in protejează sounds like the unstressed vowel in English sofa
• j in protejează sounds like the s in measure
• ch in echilibrul sounds like k here, because it comes before i
• g in biologic sounds like English j, because it comes before i

A rough English-style approximation would be:

POM-pa de A-er pro-te-ZHEA-zuh e-ki-LEE-brul bi-o-LO-jik

That is only approximate, but it can help you get started.