CLO Open-Style Calibrated Leaks




VTI’s CLO model calibrated gas leaks have a stainless steel capillary that has been precision crimped to provide an accurate flow-rate restriction for any gas. These “open-style” or “in-line” leaks do not have a reservoir of gas but, instead, use an external gas source. Under pressure, gas flows through the capillary restriction into the system or part being tested. This yields a precise, known flow rate based on the inlet and outlet pressures.

Additional Information

The CLO leaks are available welded into a tube and welded into many different inlet and outlet attachment fittings. In addition, these capillary leaks can be built into an actual or simulated test part that can then periodically be put through a regular test cycle to validate and calibrate the entire leak test system. This is the only way to be sure that the total test procedure is finding the leaks that lead to product failure. A separate brochure provides additional information.

These open-style leaks can be calibrated at one inlet pressure (your test pressure) to obtain a single specified leak rate. Alternatively, they can be calibrated at several inlet pressures, usually three, to obtain different leak rates and the ability to vary the rate within a range (usually 10x) of values using the calibration curve of pressure vs. leak rate provided.

Why choose the CLO Calibrator?

UNBREAKABLE – all stainless steel, all welded
WIDE LEAK-RATE CHOICE – use for large leak rate applications
SINGLE OR ADJUSTABLE LEAK RATES – can be calibrated at one or multiple pressures/rates
STABLE – low temperature coefficient of 0.2% / °C
CAN BE BUILT INTO A PRODUCTION TEST PART – to simulate a defect with a specific leak rate
BAKEABLE FOR UHV USE – using all metal fittings
MEETS ISO REQUIREMENTS – NIST-traceable, A2LA-accredited Calibration Certification

Ordering Information

For an order or quotation for a CLO Leak, please provide the Part Number, confirm the Inlet Fitting for connection to your gas source line, and confirm the Outlet Fitting for connection to the test system or part. It is also necessary to specify the Gas, the Inlet Pressure from your gas line, and the Outlet Pressure (usually vacuum or 1 atmosphere), all as used in your test and to be used for the calibration. Any dimensional requirements should also be noted.

In addition, for CLO’s to be used at one Leak Rate, please state the specific Leak Rate requested (at the specified Inlet and Outlet Pressure) and your preferred leak-rate units. Also, the Manufacturing Variance (“Tolerance”) that you can allow on that Leak Rate should be specified as +/- 40% (the normal allowance), or as +/- 15% (the “Special-Range Variance”), for which there is an additional cost and an “-SR” added to the part number. An example specification is 2.0×10-5 atm-cc/sec +/- 40%. In all cases, the leak rate provided will be as close as we can make it to your specified rate, and the actual rate, as calibrated, will be recorded on the Calibration Tag and the Certifications.

CLO Leaks can also be calibrated at multiple pressures to provide a range of adjustable leak rates, for example covering values from 1 to 9×10-5 atm-cc/sec using three pressures from 15 to 200 psig. VTI provides a curve of Leak Rate vs. Pressure based on the calibrations. This allows the leak rate to be changed by changing the inlet pressure and allows exact leak rates to be selected without the limitation of the manufacturing variance. For these adjustable-rate CLO’s, the Leak Rate Range requested and your available Inlet Pressure Range, as well as your Outlet Pressure, should also be specified. VTI can advise on the leak-rate range achievable based on your available pressure range.

Part Number Build Up

The CLO Series Part Numbers are constructed as follows:


where X = the code for the Leak Rate Range

where N = number of calibration points

where A = cal method – (C for He, P for other gases)

where BB = gas to be used

where YYYY = the INLET fitting required

where ZZZZ = the OUTLET fitting required

Example Gases Available

Helium (HE), Argon (AR), Nitrogen (N2), Hydrogen (H2), Carbon Dioxide (CO2), Oxygen(O2), Air (AIR), Methane (CH4), Sulphur Hexafluoride (SF6), Refrigerants (“R”#), Xenon (XE), Deuterium (D2), Mixed gases (MIX)

Example Fittings Available

Please contact us for other fitting requirements.

Code: Description:
118T 1-1/8″ OD Port Tube
4FVCR ¼” Female VCR
4MVCR ¼” Male VCR
MCFF 1.33″ OD Mini Conflat Flange
2CFF 2.75″ OD Conflat Flange
½T ½” OD Tube
KF16 ¾” OD ISO Flange
KF25 1″ OD ISO Flange
KF40 1.5″ OD ISO Flange
118T/34T 1-1/8″ OD Tube with step to ¾” Tube
4MPT ¼” Male Normal Pipe Thread

Leak Rates Ranges Available and Example Part Numbers

Leak Rate Ranges Available for the CLO Leak Range Code (X) Cal Pts & Type Code (NA) Gas Code (BB) Inlet Fitting Code (YYYY) Outlet Fitting Code (ZZZZ) Example Part Number
(Specify a value in the range for 1 cal’ point or range to be covered by 3 cal’ points)
1.0 to 9.9×10-1 atm-cc/sec 1  1C  HE  4FVCR  4MVCR  CLO-1-1C-HE-4FVCR-4MCR 
1.0 to 3.0×10-2 atm-cc/sec 2  1P  AR  4MVCR  MCFF  CLO-2-1P-AR-4MVCR-MCFF 
1.0 to 9.9×10-3 atm-cc/sec 3  3P  SF6  KF25  KF40  CLO-3-3P-SF6-KF25-KF40 
1.0 to 9.9×10-4 atm-cc/sec 4  1P  AIR  4FVCR  4MVCR  CLO-4-1P-AIR-4FVCR-4MVCR 
1.0 to 9.9×10-5 atm-cc/sec 5  1P  XE  MCFF  2CFF  CLO-5-1P-XE-MCFF-2CFF 
5×10-5 to 5×10-6 atm-cc/sec 5/6  3P  H2  1/4T  2CFF  CLO-5/6-3P-H2-1/4T-2CFF 
1.0 to 9.9×10-6 atm-cc/sec 6  3C  HE  4MPT  4MPT  CLO-6-3C-HE-4MPT-4MPT 

Additional information


> 99 atm-cc/sec, 0.1 to 9.9 atm-cc/sec, 1.0 to 99 atm-cc/sec, 1.0E-1 to 0.99 atm-cc/sec, 1.0E-2 to 9.9E-2 atm-cc/sec, 1.0E-3 to 9.9E-3 atm-cc/sec, 1.0E-4 to 9.9E-4 atm-cc/sec, 1.0E-5 to 9.9E-5 atm-cc/sec, 1.0E-6 to 9.9E-6 atm-cc/sec, 1.0E-7 to 9.9E-7 atm-cc/sec, Unknown


#2 (1/4") Female Hansen Quick Connect, #2 (1/4") Male Hansen Quick Connect, 1-1/8" OD Tube, 1-1/8" to 3/4" OD Tube, 1.33" OD Conflat Flange, 1/4" Female NPT, 1/4" Female Schrader w/ Core Depressor, 1/4" Female VCO, 1/4" Female VCR, 1/4" Male NPT, 1/4" Male O-Seal, 1/4" Male Schrader w/o Core, 1/4" Male VCO, 1/4" Male VCR, 1/4" OD Tube, 1/4" Swagelok Compression Fitting, 1/8" Female NPT, 1/8" Male NPT, 1/8" Male O-Seal, 10-32 Bolt, 3/4" Long, 2.75" OD Conflat Flange, 3/8" Male NPT, QF16 (KF16), QF25 (KF25), QF40 (KF40)


Air (AIR), Argon (AR), Carbon Dioxide (CO2), Deuterium (D2), Helium (HE), Hydrogen (H2), Krypton (KR), Methane (CH4), Mixed gases (MIX), Nitrogen (N2), Other – Please add in notes, Oxygen (O2), Refrigerants ("R"#), Sulphur Hexafluoride (SF6), Xenon (XE)


+/-10% of Target Leak Rate, +/-15% of Target Leak Rate, +/-20% of Target Leak Rate, +/-40% of Target Leak Rate – Standard, +/-5% of Target Leak Rate