Four kinds of intelligent pressure control

Four kinds of intelligent pressure control

Posted by: Leigh Moyer

From nitrogen purging or filter characterization, through vessel pressure control and leak testing applications, Alicat instruments are versatile and easy to use, while still providing excellent process control. This is because they operate with very fast control response (50-100 milliseconds) and high accuracy.

Our products are easy to program through a display interface, a serial connection or an analog connection, and we are dedicated to fast-turn-around on customized products to meet unique and variable specifications and requirements across industries. Pressure control applications can be enhanced by multivariate, rapid control, as demonstrated with these four examples.

Filter Characterization

An Alicat Pressure Controller can be used to set the pressure drop across the filter by measuring pressure before and after the filter while an Alicat mass flow meter can be used to measure the flow rate required to generate the needed pressure drop. Because mass in equals mass out, the flow meter can be placed upstream of the pressure controller as well.

Filter Test

Diagram 1

Diagram 1 illustrates a filter test using a differential pressure controller to regulate pressures before and after the filter while a mass flow meter measures flow-through at that pressure combination.

Manufactured Component Leak Characterization

Diagram 2

Diagram 2

Using an Alicat Mass Flow Meter and an Alicat Pressure Control Device, the user has a fast, accurate and reliable method for leak checking components. Our mass flow meters have full scale ranges as small as 0.5 sccm with 200:1 turndown ratio, meaning that flows as low as 0.0025 sccm (2.5 sμlm) can be resolved. If plumbed as shown in Diagram 2, the pressure is controlled at the entrance to the Device Under Test (DUT). A constant bleed though the needle valve allows the pressure controller to precisely hold the pressure at the DUT, ensuring that any flow through the meter after the bypass valve is closed is caused either by a leak or due to a cooling of the volume of the DUT. As long as the temperature of the DUT is constant, the flow reported at the meter will be the leak rate of the DUT.

High-Efficiency Helium Leak Testing

Alicat’s Dual Valve Pressure Controller is designed to prevent inefficient off gassing and to save costly gases like helium in closed-volume applications. In one kind of test, the pressure controller first removes all the air out of the test chamber then refills the chamber with helium to the desired test pressure. The gas analyzer records any helium that passes through the test device. The integrated exhaust valve of the pressure controller opens only when needed, so it maintains test pressures without continuously wasting gas through a bleed valve. See Diagram 3.

Helium leak testing using a dual valve pressure controller with pressure sensing to a helium chamber.

Diagram 3

Backpressure Control with Flow Monitoring

Backpressure control using a mass flow controller set to control on pressure.

Diagram 4

Instead of using a dedicated pressure controller and a separate mass flow meter, Alicat’s mass flow controllers (MFC) reduce equipment needs to a single instrument. This can be accomplished by setting the MFC to control for absolute pressure. The instrument will now control pressure while simultaneously displaying flow rates. As illustrated in Diagram 4, the mass flow controller allows pressure inside the system to build, simulating the internal pressure of a tire versus the air compressor that is attempting to fill it.


Specialized application engineering knowledge acquired by Alicat, for measuring and control techniques used in a wide spectrum of pressure and flow control processes, ensures that Alicat can quickly provide the optimum solution to your specific need and application, helping you create the most cost- and time-efficient system.

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