Leak Standard | MICRO-TUBE CAPILLARY | Depletion Rate | Temperature Coefficient | CALIBRATION PRESSURE | Uncertainty | WARRANTY | PRESSURE GAUGE | VALVE OPTIONS
What is a Leak Standard? A device that, under prescribed conditions, emits a controlled flow of a specified gas. This device consists of a leak element that allows gas to pass through to the outlet of the device at a controlled rate. That rate, known as the leak rate, can be accurately quantified by means of calibration.
What is a Micro-Tube Capillary Leak Element? A micro-tube capillary leak element is a flexible tube with a very small ID through which gas flows at a rate that is nearly proportional to the differential pressure across it. The leak rate of a micro-tube leak element has a positive temperature dependency of about 0.1% per °C for reservoir-style leaks, and -0.6% per °C for open-style leaks. Advantages to this leak element is that it is unbreakable; much less susceptible to plugging than crimped capillary style leaks; extremely stable; low temperature dependence;heat resistant; works with any gas; repeatable fabrication results; and leak rate stabilizes within seconds of applying gas pressure.
What is Depletion Rate? Gas Reservoir Leak Standards control the pressure and mixture of the gas upstream of the leak. Inherently, the gas supply depletes over time and as that supply diminishes, so does the leak rate. Depletion rate is an important factor in determining recalibration intervals for leak standards (typically >1 year).
Understanding depletion rate is key to the success of your application. Every LACO Tracer Gas Leak Standard is clearly labeled with the depletion rate, expressed in terms of percentage of leak rate per unit time. At any time the user can calculate the leak.
The correction is performed using the following equation:
- QCOR = the corrected leak rate (in the same leak rate unit as on the label)
- QCAL = the leak rate printed on the calibration label
- DR = the depletion rate printed on the calibration label (usually % / year)
- T = the approximate time in months since calibration
How is the Temperature Coefficient Used? A constant that allows for a leak rate correction when the leak standard is used at a temperature other than the calibration temperature. The correction is made using the following equation 1.
WHERE: QCOR is corrected leak rate (in the same leak rate unitthat is on the label), QCAL is leak rate on calibration label, CT is temperature coefficient on label (%/°C), T is ambient temperature at time of leak standard use(°C), TCAL is calibration temperature on label (°C).
EXAMPLE: The label on a leak standard shows a leak rate of2.00 x 10-6 atmcc/sec, a calibration temperature of 23.0°C, and a temperature coefficient of 2.0%/°C; the ambient temperature during use of the leak standard is 21.0°C. The corrected leak rate value, according to the above equation, is:
What is Calibration Pressure? Gas pressure needed to achieve the leak rate on the label. For open style or refillable leak standards, this pressure must be supplied during use. Do not exceed this pressure, as doing so may damage the leak standard and/or cause personal injury. Pressure in leak standards supplied with a pressure gauge should be monitored and refilled using the supplied gauge as the pressure reference (not a different gauge), as calibration of the leak standard was performed using the supplied gauge. Open-style leak standards not supplied with a pressure gauge should be pressurized using a reference pressure gauge that has been calibrated traceable to national and international standards (e.g. NIST). In many cases, the calibration pressure is denoted in relative terms (e.g. PSIG), meaning atmospheric pressure variations (due to elevation) affect this value.A correction factor to the pressure may need to be applied in these cases.
What is Uncertainty? Expressed as a percent of the leak rate. All measurements, including leak rate measurements, have a degree of uncertainty associated with them. This number defines the window, centered at the calibrated leak rate value, in which the true leak rate likely falls. For example, if a leak standard has a calibrated leak rate of 2.00 x 10-7 cc/sec and its uncertainty is ±10%, the true leak rate is likely between 1.80 x 10-7 and 2.20 x 10-7 cc/sec. NOTE The uncertainty is an expression of the calibration uncertainty, and is a function of the calibration process, not a physical property of the calibrated leak standard.
What is the Warranty for New Leak Standards? CalMaster™ calibrated leak standards are warranted to be free from defects over the lifetime of the standard. Pressure gauges used on leak standards are warranted for one year. The warranty does not cover damage to leak standards due to mishandling or improper use. The warranty is only valid while the leak standard is calibrated at LACO Technologies, Inc. on the recommended calibration interval, typically yearly. If a warranty request is made, LACO Technologies, at its own discretion, will repair or replace the leak standard, including labor and materials. Leaks that are found to be nonfunctional at time of calibration shall be repaired free of charge. The customer, however, is still responsible for the calibration cost. The customer is responsible for any and all shipping charges.
When Should a Pressure Gauge be Added to a Leak Standard? A bourdon type dial pressure gauge is installed as part of the leak standard when the leak reservoir is intended to be user-refillable, or for some open-style leaks. A pressure gauge is not recommended for leak standards when the reservoir is not intended to be user-refillable.
The pressure gauge does not require an independent calibration, as it is part of the leak standard calibration. Only the installed gauge should be used as a pressure reference for the leak.
Advantages: Allows user to monitor a leak standard's pressure status, and to refill it when necessary; makes it possible to estimate the current leak rate based on the current pressure; eliminates the need for an external pressure gauge; provides an effective solution for leaks with high depletion rates;
Disadvantages: Usually causes the leak standard to be bulkier and often awkward; the pressure gauge is the most likely component to fail, and failure may not always be evident; the accuracy of the leak rate is limited to the repeat-ability of the gauge; additional potential leak paths are introduced by installing a gauge; barometric pressure changes (primarily due to elevation) must be accounted for in pressure gauge readings
Manual Valve: The most common valve is a manually-operated two-way valve that traps leaking gas between the leak element and the valve seat when closed. Gas will continue to flow through the leak element into the "dead volume" of the valve until the pressure across the leak element equalizes.
Solenoid Valve: A 3-way solenoid valve that operates on 24 VDC that directs the flow of gas either into or away from the process, depending on its state.
Zero-Volume Valve: A zero volume valve is a manually-operated two-way valve that traps leaking gas between the leak element and the valve seat when closed. Gas will continue to flow through the leak element into the "dead volume" of the valve until the pressure across the leak element equalizes. Because the valve is designed to have very low dead volume, equalization occurs relatively quickly, effectively stopping leakage (and thus depletion) while closed. Also, due to the low dead volume, trapped gas is minimized, such that pressure burst when the valve is opened will be vastly reduced or eliminated. This valve contains parts that are not heat resistant, and therefore it should not be baked. It also contains components that may out-gas in high vacuum conditions.
Bakeable Valve: This valve contains only metal internal components, and therefore it may be baked; it is also suitable for high vacuum conditions.
What Other Options are Available for Leak Standards?
- Open Style or Reservoir Style – Provide your own gas supply or let LACO provide it for you
- Customize Your Leak Rate with Precision – 1.0E-1 atm-cc/sec to 1.0E-10 atm-cc/sec. Specify the exact leak rate values or simply request the decade of the leak rate or low, medium or high end of a decade
- Choose your Gas – LACO covers over 30 gases as standard: including Helium, Argon, numerous refrigerants, Sulfur Hexafluoride (SF6), and many more
- Output Condition – Our leak standards are manufactured to be precise at full vacuum or 10 atmospheres
- Adaptor Fittings – LACO's leak standards can adapt to any system, from NW/KF to NPT to ConFlat to compression. Our lab engineers have worked with thousands of configurations
- Isolation Valve – Isolation valves are available for manual, electrical or pneumatic control of your system
- Pressure Gauges – Add a pressure gauge to monitor and effectively control the pressure to your leak element
- Calibration Units – We will match your system with the units you prefer from Oz/Year to Atm-cc/sec
- Calibration Conditions – LACO can provide special temperature conditions when your leak standard is calibrated including water baths and utilizing various pressures for multi-point calibrations
- Special Form Factor – Our lab engineers will help you identify the right leak standard for your application – from tight fit/space-constrained applications to small self-contained leak standards designed to fit inside your part
- Special Materials – Stainless steel is our standard material; however, our lab engineers can work with other materials as required
- Multiple Leaks in Same Package – We can provide multiple leaks tied together on the same manifold controlled with valves
- Unique Applications – Our experienced engineers design all types of unique applications. Partner with LACO to meet your exacting requirements