Is request an imperative?
Also asked, is should an imperative?
"Should" is just one of many helping (auxiliary) verbs. They are not able to be used with infinitives or imperative mood infinitive-form verbs. The second sentence is a suggestion and the third is definitely commanding, but neither is in the imperative mood.
Considering this, how can you tell if a sentence is imperative?
The first indication of an imperative sentence is its punctuation. Most of these sentences end with a period, and sometimes an exclamation mark. Just be careful, as imperative sentences aren't the only sentences that end with a period or exclamation mark (as you'll see below).
The sentence which is used to convey a command, a request, or a forbiddance is called an imperative sentence. This type of sentence always takes the second person (you) for the subject but most of the time the subject remains hidden. Examples: Bring me a glass of water.