ENGINEERING OF WATER SYSTEMS

摘要

We discussed the concepts associated with designing effective conveyance systems, usually referred to as valving, for pumping stations and water systems in the past several installments of The Water Works. In Part 5 of this subseries, we'll wrap up the discussion with greater detail about the various types and applications of control valves used for these systems. Another group of valves commonly used on pumping plants are automatic control valves. These valves, usually constructed using a globe valve, are most often used on the discharge side of pumps to control flow or pressure. They utilize the principle of force differential from pressure applied from a larger surface area on the top of a diaphragm than the area of the valve disc. Although there are as many types of control valves as there are applications, we will limit our discussion to pilot controlled, hydraulically operated, diaphragm-type control valves for the purposes of this column. This is not intended to ignore other types of valves such as actuator-controlled butterfly valves or ball valves used for fluid control, but rather to compare the type of control valve most often compared to variable frequency drives. Diaphragm-type control valves operate on the principle of force differential. For any given valve, the surface area on the top of the diaphragm is much larger than the area of the valve disc or seat. This provides the necessary differential of surface area.