Mechanism of interaction of pressure waves at a discrete partial blockage

• We examined the transient response of discrete partial blockages of different geometrical characteristics.
• Laboratory and numerical experiments concerned both valves and small bore pipe devices simulating a partial blockage.
• Experiments pointed out that two mechanisms of interaction between pressure waves and partial blockages can occur.
• The mechanism of interaction depends on the path of pressure waves through the partial blockage.
• The effect of the pre-transient conditions was examined.

This paper analyses the mechanism of interaction between an incident pressure wave and blockages of different geometrical characteristics (i.e., a butterfly and a ball valves, two short stretches of pipe with a reduced diameter, and a device simulating a longitudinal body blockage) by means of laboratory and numerical tests. Experiments have shown that the mechanism of interaction with pressure waves is influenced by their path through the device: sinuous because of the device body for partially closed in-line valves (type I mechanism), and straight for the small bore pipe devices (type II mechanism). Type I mechanism is characterized by a rise followed by an almost constant value whereas in type II one a drop occurs after the rise. To complete the investigation the effect of the pre-transient condition is discussed.