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The importance of good definitions

Sep 29, 2017

Cavagna Group S.p.A. | The importance of good definitions

Clear definitions (that are understood and agreed upon by all parties) are essential. This document is intended to help to set common definitions and is an essential tool for a successful understanding when discussing about VIPR. A VIPR is a cylinder valve with an integrated pressure regulator used to reduce the high cylinder pressure to a lower pressure suitable for use.

Who if not ISO set the standards for harmonisations of terms and definitions? So, We Cavagna Group, also take ISO as a reference.

Definitions below come from the document called ISO 22435:2007(en) Gas cylinders — Cylinder valves with integrated pressure regulators – Specification and type testing. ISO 22435 was prepared by Technical Committee ISO/TC 58, Gas cylinders, Subcommittee SC 2, Cylinder fittings.

VIPR Terms and definitions:

adjustable pressure regulator
device that has been provided with a means of operator adjustment of the delivery pressure under normal use

closure pressure
stabilized outlet pressure, one minute after cessation of the flow, from a pressure regulator by which the flow has been set to a standard discharge

cylinder valve with integrated pressure regulator
device intended to be permanently fitted to a gas cylinder connection and comprising a shut-off valve system and pressure reduction system

filling port
point on the device through which the cylinder is filled

flow characteristic
variation of the outlet pressure in relation to the rate of flow from zero to maximum capacity flow of the pressure regulator with the inlet pressure remaining constant

flow gauge
device that measures pressure and that is calibrated in units of flow

device that measures and indicates the flow of a specific gas or gas mixture

lagging of the outlet pressure (effect) when the flow (cause) is varied so that at a constant inlet pressure the values of outlet pressure measured with increasing flow do not coincide with the values of outlet pressure measured with decreasing flow

maximum discharge flow
maximum flow which is delivered by the pressure regulator at the rated outlet pressure, p2, and at the test inlet pressure, p3

restriction of known cross-section that delivers a constant flow of gas when supplied with gas at a constant upstream pressure

pre-set pressure regulator
pressure regulator that has not been provided with a means of operator adjustment of the delivery pressure under normal use

pressure characteristic
variation of the outlet pressure with inlet pressure under specific initial flow conditions

pressure regulator
device for regulation of a generally variable inlet pressure to an outlet pressure as constant as possible

main shut-off mechanism
shut-off valve between the gas cylinder and the regulating mechanism of the device

rated outlet pressure
downstream pressure for the standard discharge, Q1, specified in the instructions for use

pressure relief valve
device designed to release excess pressure from the outlet side of the pressure regulator at a pre-set value

secondary operating mechanism
means of setting the outlet discharge flow between zero and maximum

standard discharge
flowrate, specified in the instructions for use for which the pressure regulator is designed to maintain a rated outlet pressure, p2, at test inlet pressure, p3

test inlet pressure
inlet pressure at which the standard discharge of the pressure regulator, Q1, is measured and which is twice the rated outlet pressure, p2, plus 100 kPa, i.e. p3 = (2 p2 + 100 kPa)

test outlet pressure
highest or lowest value of the outlet pressure resulting from a variation in the inlet pressure between p1 and p3 at previously adjusted conditions p1, p2, Q1

valve test pressure
for compressed gases, pvt = 1,2 × pw;
for liquefied gases and dissolved gases under pressure (e.g. acetylene), pvt is at least equal to the minimum test pressure of the cylinder quoted in the relevant transportation regulation for that gas or gas group

working pressure

settled pressure, at a uniform temperature of 15 °C, for a full gas cylinder

Note 1 to entry: For compressed gases, pw in this International Standard corresponds to p1 in ISO 2503.

Note 2 to entry: This definition applies only to compressed gases and not to liquefied gases and dissolved gases (acetylene).

For over 60 years Cavagna Group has been designing, developing and manufacturing Valves and Regulators for compressed gas containers. Today Cavagna Group is out-front in the development of VIPRs. Our I-VIPR valves have been designed to be safe, reliable and multipurpose.

Cavagna Group