PSO Calibrated Leaks




These capillary-type calibrated leaks use VTI’s proprietary Positive Shut-Off (PSO) valves to provide instant on-off operation with essentially no dead volume. This eliminates any gas burst when the valve is opened. The valve’s dead volume is only 0.0001 cc compared to as much as 1 cc or more in some valves. The PSO-valve Leaks also minimize gas depletion rates and provide longer life even at high flow rates. Their leak-rate control element is a crimped stainless steel capillary suitable for use with all gases.

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Additional Information

“] The Positive Shut-Off Calibrated Leaks are available with an integral gas reservoir and can be provided with any gas. They are also available without a gas cylinder for use with an external gas source. Operation of the valve can be manual, pneumatic or electrical.

The unique features of these proprietary PSO Calibrated Leaks result in their use in a wide variety of applications. They are extensively used for verification tests and calibration of Leak Testing Systems, usually with automated valve operation and usually with an external gas source rather than a reservoir. They are also used frequently to flow gas at a controlled rate into a process chamber or research apparatus, or to “dope” another gas stream. For mass spectrometer analysis of gases that are at high pressures, the PSO-valve Leaks are used to reduce the pressure and provide a sample rapidly with no gas burst.

VTI has also developed a Mass Spectrometer Calibrator using the PSO Calibrated Leak and a reservoir of mixed gas (3% Helium, Krypton, Xenon and Hydrogen, 1.8% Nitrogen and 86% Argon). This Mixed-gas Calibrator provides a convenient and accurate way to tune the peak position and height for masses ranging from 1 to 132 amu. The low dead volume of the valve eliminates any gas burst into the system and conserves the gas mix, thus providing a long operational lifetime.

Why choose the PSO Calibrator?

ESSENTIALLY NO DEAD VOLUME – no pressure burst on opening
LOW DEPLETION RATES – allows high flow rate applications and use with expensive gases
FAST RESPONSE – provides instant on-off operation
AUTOMATIC OPERATION – for system integration
LONG TERM STABILITY – valve is closed except during use
MEETS ISO REQUIREMENTS – NIST-traceable, A2LA-accredited Calibration Certification
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Ordering Information

“] For an order or quotation request for a PSO Leak, please provide the Part Number constructed from the codes provided, and also confirm the Fittings by name and function to avoid errors. In addition, please describe the Gas or Gas Mix to be used. Any dimensional requirements should also be noted.

For the PSO Leaks with a Reservoir, please also specify the specific Leak Rate requested and your preferred leak-rate units. For PSO Leaks without a reservoir to be used at one leak rate and pressure, please provide the specific Leak Rate requested, plus the Inlet Pressure that you will use from your gas line (corresponding to that Leak Rate). In either case, the Outlet Pressure should be stated as “Flow into Vacuum” (the usual) or “Flow into Atmosphere” (1 atm.). 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 both 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.

PSO Leaks without a reservoir can also be calibrated at multiple inlet 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 your pressure and allows exact leak rates to be selected without the limitation of the manufacturing variance. For these adjustable-rate PSO Leaks, VTI can advise on the leak-rate range achievable based on your available pressure range.

Part Number Build-Up

The PSO Series Part Numbers are constructed as follows:

For leaks without a resevoir:


For leaks with a resevoir:


where T = operation (M=Man, A=Air, S=Solenoid)

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

where OOOO = the OPTIONAL port fitting

where RRRR = the reservoir required

where FVO = the Fill Valve Option – WFV, MFV

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:
4FVCR ¼” Female VCR
4MVCR ¼” Male VCR
MCFF 1.33″ OD Mini Conflat Flange
2CFF 2.75″ OD Conflat Flange
KF16 ¾” OD ISO Flange
KF25 1″ OD ISO Flange
4MPT ¼” Male Normal Pipe Thread

Other Ordering Codes

X Code: Leak Rate Range:
2 1.0 to 9.9×10-2 atm-cc/sec
3 1.0 to 9.9×10-3 atm-cc/sec
4 1.0 to 9.9×10-4 atm-cc/sec
5 1.0 to 9.9×10-5 atm-cc/sec
6 1.0 to 9.9×10-6 atm-cc/sec
R Code: Reservoir Size:
150DOT 150cc tested per DOT
300DOT 300cc tested per DOT
1000DOT 1000cc tested per DOT

Example Part Numbers

PSO-valve Leak with a Reservoir Part Number:


An Argon leak with manual valve operation, one specified leak rate in the range of 10-6 atm-cc/sec, VCR fittings, 300cc reservoir and an all-metal fill valve.

PSO-valve Leak without a Reservoir Part Number:


A Helium leak with an air-operated valve, calibrations at 3 rates/pressures in the range of 10-5 atm-cc/sec and VCR fittings.

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Additional information


Automatic, Manual


Comparison Calibration Method, Primary Calibration Method


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)


2CFF 2.75" OD Conflat Flange, 4FVCR ¼" Female VCR, 4MPT ¼" Male Normal Pipe Thread, 4MVCR ¼" Male VCR, KF16 ¾" OD ISO Flange, KF25 1" OD ISO Flange, MCFF 1.33" OD Mini Conflat Flange, Other – Please add in notes


2CFF 2.75" OD Conflat Flange, 4FVCR ¼" Female VCR, 4MPT ¼" Male Normal Pipe Thread, 4MVCR ¼" Male VCR, KF16 ¾" OD ISO Flange, KF25 1" OD ISO Flange, MCFF 1.33" OD Mini Conflat Flange, Other – Please add in notes


2CFF 2.75" OD Conflat Flange, 4FVCR ¼" Female VCR, 4MPT ¼" Male Normal Pipe Thread, 4MVCR ¼" Male VCR, KF16 ¾" OD ISO Flange, KF25 1" OD ISO Flange, MCFF 1.33" OD Mini Conflat Flange, None, Other – Please add in notes