What is the relationship between valve bore size and medium flow rate?

The flow rate and velocity through a valve are primarily determined by its nominal bore, and are also related to the structural resistance it presents to the medium. Simultaneously, they maintain an intrinsic relationship with various factors such as the medium's pressure, temperature, and concentration.

What precisely is the relationship between these factors?

The flow channel area of a valve has a direct correlation with flow velocity and flow rate, which are two interdependent quantities. When flow rate is constant, a higher velocity permits a smaller flow channel area; conversely, a lower velocity allows for a larger flow channel area. Conversely, a larger flow channel area results in lower velocity, while a smaller flow channel area yields higher velocity.

A higher fluid velocity permits a smaller valve bore, but this incurs greater pressure loss and increases susceptibility to valve damage. High velocities may generate electrostatic effects with flammable or explosive media, posing hazards; conversely, excessively low velocities result in inefficient and uneconomical operation. For highly viscous or explosive media, lower velocities should be employed. For oils and high-viscosity liquids, velocity selection depends on viscosity, typically ranging from 0.1 to 2 m/s.

Typically, flow rate is predetermined, with velocity established empirically. Valve nominal diameter can be calculated from velocity and flow rate. Valves of identical nominal diameter yet differing structural designs exhibit varying fluid resistance. Under identical conditions: - A higher valve resistance coefficient results in greater reductions in both flow rate and velocity through the valve; - A lower valve resistance coefficient leads to lesser decreases in velocity and flow rate through the valve.