Question

In Back pressure type pneumatic gauge, there are two orifices. What is the relationship between upstream pressure of first orifice and pressure between two orifices?

(a) Depends upon the distance between two orifice

(b) Depends upon relative size of orifice

(c) Only on geometric area of first orifice

(d) Distance between pressure source and first orifice

The question was posed to me in class test.

The query is from Pneumatic Comparators in section Comparators of Engineering Metrology

Answer 1

The correct choice is (b) Depends upon relative size of orifice

The best I can explain: Upstream pressure and pressure between both orifices, they both are measured with reference to atmospheric pressure. The relationship between both the pressures depends upon relative sizes of the two orifices.