What is the purpose of using Y-type strainer along with flow meters?

Y Type of strainers are designed to protect flow meters from potential damage due to mud and other outside particles that may be tote by the process fluid in a pipeline. Y Type Strainers are generally used where high flow capacity is a must. The Strainer boosts the clearance in the Fluid, and improve the life of conventional valves. Protects expensive pumps, flow meters and other flow measuring equipment. It is suitable for water, Air, Gas, petroleum, steam, and other fluids.
It can be installed vertically or horizontally as per requirement. You can know more from y strainer manufacturers,
http://www.lntindustries.in/y-type-strainers.php