Leak Detection System and Method
Leak Detection System and Method
This document presents a patented method for testing ASDevices valves during development and manufacturing, focusing on quality control. The system is portable and beneficial for valve and fitting manufacturers, as well as process plant start-up teams. It is particularly effective for detecting 'capillary' type leaks using nitrogen as a tracer gas, offering enhanced sensitivity compared to helium-based systems.
Leaks are classified into 'capillary' and 'orifice' types. Orifice-type leaks involve fluid passing through a channel with a length similar to or less than its diameter, easily detected with small molecule gases like helium. Capillary-type leaks have a channel length much greater than the diameter, better detected with low viscosity gases like nitrogen.
The system uses nitrogen instead of helium, making it more affordable and sensitive for capillary-type leaks. It involves a Valve Under Test (VUT) connected to a nitrogen source, with an argon purge to evacuate air. The system uses a Plasma Emission Detector (PED) for nitrogen measurement, offering high sensitivity and specificity.
The testing involves several steps:
- Step 1: Install and secure the VUT, purge atmospheric air using argon.
- Step 2: Switch valve positions to allow argon purge through the VUT, with the PED measuring nitrogen levels.
- Step 3: Adjust inlet pressure in steps, monitoring nitrogen levels to detect leaks.
- Step 4: Depressurize and prepare the system for the next cycle.
The system includes electronic control and signal conditioning subsystems, with amplification and conversion for precise leak measurement. It uses different emission wavelengths for varying nitrogen levels, with optical filters and photodiodes for detection.
This nitrogen-based leak detection system offers a cost-effective and sensitive solution for detecting capillary-type leaks, with advantages over traditional helium-based systems.
The document describes a leak detection system with a user interface that graphically represents impurity readings. This system allows for efficient monitoring and recording of leak results, which can be networked and reported to a remote control system or PC.
Recycling: The system can include a gas recycling feature to reduce gas consumption, beneficial for portable systems. It involves a pump, purifier, and flow restrictor to maintain desired flow and pressure, ensuring minimal baseline shift.
Detection System and Tracer Gas: The system can operate with different PED and gas combinations, such as using helium instead of argon. Operating under vacuum conditions can enhance sensitivity and reduce noise.
Figure 1: Illustrates different leak types and flow zones.
Figure 2: Shows a possible embodiment of the leak detection system.
Figure 3: Demonstrates an impurity signal example.
Figure 4: Depicts an acceptable range band for pressure.
Figure 5: Highlights the impact of pressure changes on system signals.
Figure 6: Provides a schematic of the sampling system test.
Figure 7: Compares leak detection sensitivity across various techniques.
Includes components like pressure transducers, valves, pumps, and purifiers, each with specific functions to ensure system efficiency.
The document includes a disclaimer regarding the proprietary nature of the information and the necessity for verification in real applications.
References a study on interference-free measurement of N2 in Argon and Helium.
Catalog excerpts
Leak Detection System and Method The most sensitive technology for valve quality control Date: July 2015, updated in January 2024
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exposed to atmospheric air, where, generally speaking, there is a 5 PPM helium content. The following patented method is used to test all ASDevices valves during development and for quality control during manufacturing. Sensitivity could be increased by using a helium cylinder instead of relying on the helium content of atmospheric air. Such a leak detection system is calibrated by pumping atmospheric air or helium into the mass spec, through a calibrated leak orifice. It is mainly useful for a “capillary” type leak. Here we classify leaks into two large categories, i.e., capillary and orifice...
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Considering all the above-mentioned facts, we have designed a leak detection and measuring system based on N2 instead of helium. This system is suitable for capillary and permeation type leaks, as we will demonstrate here. Figure 2 shows one possible embodiment of the system. System Description Testing Valve First, the Valve Under Test, i.e., VUT, is installed into the system. Here an ON/OFF valve of any type is shown, i.e., could be a diaphragm-based, ball, globe, etc. The size is not an important issue, since the purge argon flow is adjusted accordingly. The inlet of the VUT is connected to...
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valves will have a longer waiting time. During the N2 inlet pressure stepping sequence, the PED measures N2 signal and reports it to the signal processing subsection. If there is a diminution of the slope value of the signal S, N2 is flowing through a leakage passage of VUT. Here the differential value could be measured to report the PPM of N2 and transform it in the desired leak rate engineering unit. A band could be defined above the slope signal where the leak rate could be acceptable (see Figure 4). Before each pressure increase, the system baseline is re-zeroed, so that monitoring is done...
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During the execution of a leak-finding procedure, the signal value may decrease and go under scale because the atmospheric or residual N2 is being purged out by the action of argon flowing and purging the outlet side of VUT. At this point, it becomes necessary to set back the signal on scale by offsetting it, at a predetermined value. For example, 50% of the scale, other values will work too. It may be desirable to change this value based on operating conditions, mainly the valve size, or the dead volume to be purged. These affect the rate or speed of the purging effect. So, when the signal decreases...
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AUTO ZERO GAIN CONTROL GAIN CONTROL GRAPHICAL DISPLAY Figure 2 – Leak detection possible embodiment. SIGNAL PROCESSING OPTIONAL GAS RECYCLING SYSTEM Visual Indication DIGITAL I/0: • Control various ON/OFF valves, like V1, V2 and V5 ANALOG I/0: • Read various parameters like pressure and flow • Control V5, PC1, V3
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Bill of Material for Figure #2 PC1: High-pressure electronic pressure controller based on a proportional EDV-1. PT1, PT2, PT3: Absolute pressure transducer V1: Diaphragm type stream selection valve, ASDevices EDVS-4. V2, V4: Diaphragm type 3-way switching valve ASDevices EDV-3. V3: Tight shut-off proportional valve based on ASDevices EDV-1. V5: Diaphragm-based proportional valve based on ASDevices EDV-1. V6: Diaphragm-based ON/OFF valve, ASDevices EDV-1. CV1: Check the valve to prevent back flow when using the recycling system. PF: Particle filter. TRAP: Tube having proper gettering material...
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Figure 7 – Leak Detection Sensitivity Comparison Leak Detection Techniques Bubble test (soap painting) NB: A leak rate of 1.E-14 atm cc/s would need 3 million years to pressurize a cube of 1cc from complete vacuum to atmospheric pressure. Bubble test (He, alcohol) Water immersion (bubble test) Acoustical Pressure decay (without pressure differential) Pressure decay (withpressure differential) Vacuum decay Thermoconductivity Halogen sniffer Helium sniffer (inside-out) Helium leak test outside-in Vacuum chamber helium leak test (inside-out) 1.E+02 Leak Rate (mbar l/s or atm cc/s) References [1]...
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