End face mechanical seal - Seal categories. 1  All mechanical seals must contain the four elements described above but the way those functional elements are arranged may be quite varied. 2  Mechanical seals are generally classified into two main categories: Pusher or Non-Pusher.
The past modal perfect tense begins with any past tense modal (could, should, would, might) followed by âhave,â plus a past tense action verb (regular verbs ending with â-edâ and many irregular verbs ending with-en).
Best Answer: Erik, let's keep it simple: 1. The present perfect tense is used to describe past events whose results/consequences are somewhat relevant at the moment of speaking; thus the word 'present' in the name of the tense. Me he divertido (I have had fun) suggests that the speakers had fun very recently.2.est Answer: Erik, let's keep it simple: 1. The present perfect tense is used to describe past events whose results/consequences are somewhat relevant at the moment of speaking; thus the word 'present' in the name of the tense. Me he divertido (I have had fun) suggests that the speakers had fun very recently.