Cast iron Y strainers  are typically used in applications where the amount of solids to be removed is small, and where frequent clean-out is not required.  They are most often installed in gaseous services such as steam, air, nitrogen, natural gas, etc.  The compact, cylindrical shape of the Y-strainer is very strong and can readily accommodate the high pressures that are common in this type of service.  Pressures up to 6000 psi are not unusual.