Tôi vặn van khóa thay vì lau tường.

A simple way to see it is:

• Tôi = subject
• vặn van khóa = first action
• thay vì = instead of / rather than
• lau tường = alternative action

So the pattern is basically:

Subject + verb phrase + thay vì + verb phrase

Vietnamese often follows a clear Subject–Verb–Object order, so this sentence is structurally quite straightforward.

Vặn means to twist or to turn by twisting.

That is why it fits well with things like:

• vặn vòi nước = turn the faucet
• vặn nắp chai = twist the bottle cap
• vặn van = turn the valve

A useful nuance:

• vặn focuses on the physical twisting motion
• mở or đóng focus more on the result: open or close

So with a valve:

• vặn van = turn the valve
• mở van = open the valve
• đóng van = close the valve

Here, van khóa is understood as a compound noun meaning something like shut-off valve or stop valve.

• van = valve
• khóa literally can mean lock or close off
• together, van khóa refers to a valve used to shut something off

So in this sentence, it is best to read van khóa as one noun phrase, not as two separate ideas.

In Vietnamese, the main noun usually comes first, and words that describe or narrow it often come after.

So:

• van khóa = a valve of the shut-off type
• bàn gỗ = wooden table
• xe tải = cargo truck

This is different from English, where modifiers often come before the noun.

Thay vì means instead of or rather than.

It is commonly followed directly by:

• a verb phrase
• a noun phrase
• sometimes a longer clause

In your sentence:

• vặn van khóa = action actually done
• lau tường = action not done

So thay vì lau tường means instead of wiping the wall.

A similar example:

• Tôi đọc sách thay vì xem TV.
• I read books instead of watching TV.

Vietnamese does not have articles like English a, an, and the.

That means nouns like van khóa and tường can appear by themselves, and the exact sense is understood from context.

If a speaker wants to be more specific, they might add other words, for example:

• cái van khóa đó = that valve
• bức tường này = this wall

But in many normal sentences, Vietnamese simply leaves the noun bare.

Yes. Lau usually means to wipe, to clean by wiping, or sometimes to polish depending on context.

So lau tường means something like:

• wipe the wall
• clean the wall by wiping it

It is a surface-cleaning verb. If you wanted a different kind of action, Vietnamese would often use a different verb:

• rửa tường = wash the wall
• cọ tường = scrub the wall
• sơn tường = paint the wall

So lau is a good choice if the action is specifically wiping/cleaning the surface.

By itself, the sentence does not explicitly mark tense.

Vietnamese often leaves time reference to context. So depending on the situation, this could mean:

• I turn the valve instead of wiping the wall
• I turned the valve instead of wiping the wall
• I will turn the valve instead of wiping the wall

If you want to make the time clearer, Vietnamese often adds markers like:

• đã = past
• đang = ongoing
• sẽ = future

Examples:

• Tôi đã vặn van khóa thay vì lau tường.
• Tôi đang vặn van khóa thay vì lau tường.
• Tôi sẽ vặn van khóa thay vì lau tường.

Sometimes yes, if the subject is already obvious from context.

Vietnamese often drops pronouns when they are understood. But without context, keeping Tôi makes the sentence clear and complete.

So:

• Tôi vặn van khóa thay vì lau tường. = fully clear on its own
• Vặn van khóa thay vì lau tường. = possible in context, but more dependent on what came before

Yes. Vietnamese allows that, especially for emphasis or contrast.

For example:

• Thay vì lau tường, tôi vặn van khóa.

This means the same basic thing, but it puts more emphasis on the instead of wiping the wall part.

Your original sentence is more neutral and direct:

• Tôi vặn van khóa thay vì lau tường.

Both are grammatical.

Yes, it is grammatical and understandable.

The only thing to notice is that the situation itself is a bit unusual: turning a shut-off valve instead of wiping a wall is not a very everyday contrast, so it may sound slightly odd because of the scenario, not because of the grammar.

Grammatically, though, the sentence is fine:

• Tôi = subject
• vặn van khóa = normal verb + object phrase
• thay vì lau tường = normal instead of phrase

So a learner can safely study it as a good example of how thay vì links two actions.