Final answer:
The Weir diaphragm valve is best suited for handling products containing solids or viscous fluids due to its design that minimizes contact between the diaphragm and the fluid.
Step-by-step explanation:
The type of diaphragm valve that is best suited for products containing solids or viscous fluid is the Weir diaphragm valve. This type of valve is designed with a raised saddle or weir in the body of the valve, which allows for the controlled passage of fluids.
The design of the weir diaphragm valve means that when the valve is open, there is minimal contact between the diaphragm and the fluid. This characteristic is important as it reduces the chances of the diaphragm being damaged by solid particles and ensures better handling of viscous fluids compared to other types of diaphragm valves.