May 7, 2015

Alicat has developed the Whisper line of mass flow instruments to meet the needs of customers whose processes were too sensitive for traditional flow measurement and control instruments. Having very little pressure drop, a Whisper can be added to a system without inducing back pressure or significantly affecting volumetric flow measurement.

“Invisible” flow measurement

Alicat Whisper mass flow meter

Whispers solve a long-standing problem for customers with low pressure flow requirements: Flow measurement technologies change the very flow conditions they are designed to measure. This is especially apparent when working with volumetric flows, whose rates change as the line pressure increases or decreases. Adding a flow meter consumes some of the line pressure, thus changing the actual volumetric flow rate as it is being measured.

Employing both a flow path that virtually eliminates pressure drop (consumption of line pressure) and a custom sensor that is powerful enough to measure the little differential pressure that remains, Whisper flow meters operate with minimal impact to flowing processes. Whispers are nearly invisible to the flow stream and therefore able to monitor flow without changing the rate. This is especially noticeable when measuring volumetric flows or calibrating volumetric flow instruments such as variable area meters, making Whispers ideal for these applications.

Flow regulation at atmospheric pressures

Alicat Whisper portable mass flow meter with TFT display

Adding a meter to a gas stream can additionally introduce back pressure that can constrict or halt flows with little line pressure. In the case of process analysis, added back pressure can also interfere with the measurement accuracy of in-line process analyzers. Portable Whisper meters are ideal for validating the flow in these applications with minimal impact to the actual process.

The very low pressure drop of Whisper mass flow instruments also allows them to monitor or control flows just above or below atmospheric pressures. Where most flow controllers would be unable to achieve full-scale flows, Whisper mass flow controllers can reach flows as high as 1,000 SLPM with less than 50 mbar of pressure drop. A gas analysis system for environmental monitoring can employ a Whisper flow controller to draw air through the analyzer using very soft vacuum. Likewise, atmospheric research conducted at high altitudes can make use of the very low pressure drop of the Whisper series to negate the limitations of decreased atmospheric pressure.

Responsive flow measurement and control for leak testing

Alicat Whisper mass flow controller

A special application for Whisper mass flow controllers is leak testing, as well as flow characterization. The typical setup for the mass air flow method of leak testing requires a pressure controller to maintain leak test pressures and a mass flow meter to monitor leak rates. Because Alicat pressure-based flow controllers have the capability to control pressure while monitoring mass flow rates, a single Whisper-series flow controller can single-handedly accomplish the task of leak testing. The minimal internal restrictions of the Whisper controller give it exceptionally fast response in reading leak rates while maintaining leak test pressures. The same characteristics make flow characterization processes very easy and efficient.

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