In the section of the psv If it never opened or opened for a long time. When it is opened from the first cause, could allow dirt to clean valve seat and disc are between. Thus causing the leak.
The psv if it did not open at all or open infrequently. When it opened, the first may cause the dirt to stand between disc and seat valve, thereby causing the leak.
In the part of PSV if it never opened or open once in a while. When it opened the first could be a dirt blocking between disc seat valve and can cause การรั่ว.