Home » Flapper Nozzle Questions
Practical Questions

Flapper Nozzle Questions

One of the most basic components of a pneumatic instrument is the so-called flapper/nozzle, or baffle/nozzle assembly. It consists of two restrictions to air flow, one within a tube (the orifice) and the other at the end of a tube (the nozzle).

The flapper, or baffle, is nothing more than a flat piece of metal in close proximity to the nozzle tip. These mechanisms serve as extremely sensitive position detectors, generating a pneumatic pressure output signal that varies with flapper (baffle) position:

Flapper Nozzle

Suppose that two pressure gauges were installed along the length of the tube, one upstream of the orifice and the other downstream of the orifice, like this:

Pressure Gauge upstream of the orifice

Qualitatively speaking, what would these two pressure gauges indicate? Assume that the air supply is regulated by a pressure regulator, and so remains at a constant pressure. Would the two pressure gauges indicate the same amount of pressure? Would one of them indicate a higher pressure than the other? Explain your answer.

If the flapper (baffle) is brought closer to the nozzle, the nozzle will become more restrictive to air flowthrough it. What effect will this have on the two pressure gauge indications in this flapper/nozzle system?

Baffle Nozzle

If the flapper travels further away from the nozzle, what effect will it have on the two pressure gauges’ indications?

Flapper Moved Away from Nozzle


The pressure gauge downstream of the orifice will indicate a lower pressure than the gauge upstream of the orifice. Moving the flapper closer to the nozzle increases the downstream pressure, while moving the flapper away from the nozzle decreases the downstream pressure.

Follow-up question: sketch a schematic diagram for an electrical circuit analogous to this pneumatic“circuit” formed by the pressure source, orifice, nozzle, and flapper.

Share your answers with us through the below comments section.

Read Next:

Credits: Tony R. Kuphaldt

Share With Your Friends

Related Articles

Differential Pressure Transmitter with 5 Way Manifold Valve

S Bharadwaj Reddy

Identify High Flow Alarm and Low Flow Alarm ?

S Bharadwaj Reddy

Overhead Product Pressure Control Loop

S Bharadwaj Reddy

Problem on Solar Hot Air Collector and Variable Speed Fan

S Bharadwaj Reddy

Calculate Differential Pressure Sensed by Level Transmitter

S Bharadwaj Reddy

Liquid Flow Control Loop Controller Action

S Bharadwaj Reddy

Leave a Comment

This website uses cookies to improve your experience. We'll assume you're ok with this, but you can opt-out if you wish. Accept Read More

Flapper Nozzle Questions

WordPress Image Lightbox
Send this to a friend