Application note A049-GP06

Pressure control for leakage test of gas couplings

In this application note you can read about a flow-pressure solution supplied to a coupling manufacturer in the US. The flow-pressure solution is used to conduct a leakage test as part of the quality control of the gas couplings. these gas couplings need to be gas tight during a certain minimum period in the occasion of fire.  

Leak test of gas couplings
During the test the gas coupling is mounted at the end of a tube, which is put in a furnace that is heated to a certain constant temperature. Then the setup is subjected to 10 bars (139.5 psi) of air overpressure. A coupling passes the test when the air leakage during a certain amount of time is below a prescribed value. 

Check out the Bronkhorst solution

Application requirements

In the original setup (a flow meter based on the pressure drop principle), the pressure sensor malfunctioned often, because of the high flow. With the Bronkhorst flow-pressure solution the flow cannot be higher than the full-scale range of the mass flow controller.

The coupling manufacturer needed a compact plug & play system, which is easy to operate with only one input and one output for the air flow and the rest ‘out of sight’. Furthermore, a filter is necessary to prevent soot from the furnace entering the measuring device.

Important topics

  • Pressure management with flow control
  • Plug & Play system

Process solution

Bronkhorst’s Flow-Pressure Solution comprises a pressure meter, which is a pressure sensor that controls a flow controller upstream. The pressure sensor and flow controller are special built-in units which can be used in the E-8000 control systems. When the gas coupling fails during testing, the pressure meter detects a pressure that is lower than the initial 10 bars, after which it forces the flow controller to generate an air flow into the system. At that point, when this flow has a non-zero value, a leakage is detected. According to the coupling manufacturer, the system is robust with reliable pressure sensing.

For this leakage testing application, a combination of a pressure meter/flow controller is better than a traditional combination of a pressure controller/flow meter. In the latter case, there may be a risk of losing signal in the initial period when a pressure controller wants to reach its setpoint very fast. The advantage of Bronkhorst’s setup is that the generated flow can never be too high.

Flow scheme
Flow scheme

The setup comprises a 15 μm filter to prevent soot particles from the furnace to enter the flow controller, which is detrimental for this device. In case of blockage, this filter can be cleaned by back-flushing of air, so there is no need for disassembling the setup to clean the filter. 

By default, the setup is delivered with a digital control panel to control and display the settings. Via an RS-232 serial port the control panel can be connected to a computer system using Bronkhorst’s own software. If desired a modification can be made where a potentiometer is incorporated to adjust the settings manually. This modification includes analog-to-digital switch.

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