Good guys!

I came cross to this sentens in API551 n sec 2.3.1.2.3 but displacement is unfamiliar for me,it should be a quntity of volume as it uses cubic inch for its dimension.I would like ask you to give me a clue.

Thanks
Masoud

Sorry the sentense is as follows:
"if the displacement is greater than 1cubic inch or if the differential of the instrument is low compared wuth the column displacement, regular condense pots should be used."

I assume your interest is academic, I can't believe anyone can afford DP with a bellows transmitter/recorder nowadays.

I have the 1993 API 551. The statement you cite compares the relatively large displacement of a mechanical DP bellows with the relatively small displacement of a diaphragm transmitter described in 2.3.1.2.2 in the preceding paragraph, "Because of their low displacement, these instruments can generally be used without a seal or condensate pot." By example, a Rosemount 3051's volumetric Displacement is less than 0.005 in3 (0,08 cm3).

The drawings below show the large chambers surrounding the low and high side bellows which the port supplies with fluid from the sensing line. Any volume of fluid into or out of the chamber is "displacement". The label identifying it as a diaphragm flow recorder is based on a diaphragm (literally a stack of diapragms) used for low pressure sensing, whereas a bellows were used for higher pressure sensing.