The standard test methods for cross-port and outport leakage ensure valve performance at pressures and temperatures up to the specifications listed. For valves used on mass spectrometers or for ultra-trace fixed gas analysis, we recommend an optional test method utilizing a helium mass spectrometer. (More below)
Leak rates for gas sampling valves
The actual minimum leak rates attainable vary widely with seal material and valve type. In general, the acceptable leak rates fall into three ranges, noted in the right column.
In order to seal to less than 10-7, the valve loading tension is increased, which somewhat lowers the maximum operating temperature and the valve lifetime. Currently, only select material can seal to 10-8 in most valve styles. Valcon M rotor material can seal to 10-10, but has a temperature limit of 50°C.
Not all valves can achieve these leak rates. As a general rule, the larger the valve seal and port size, the higher the leak rate.
Test method for liquid sampling valves
The standard test method for liquid valves is a pressure drop over time for both crossport and outport leakage, using isopropanol at the specified test pressure. This test is designed to ensure proper performance at the specification limit.
Optional leak testing with helium mass spectrometer
This optional test method utilizes a helium mass spectrometer, which provides data on mechanical leaks and on those due to seal porosity and permeability. With this method, we can certify leak rates as low as 10-10 cc-atm/sec.
To order a valve certified to have helium leak rates less than 10-7 cc-atm/sec, add the suffix "Z" to the valve product number and contact us about the additional price.
Certified valves are supplied with gold-plated stainless steel ferrules.
Please consult the factory prior to ordering, since the minimum leak rate will vary widely depending on valve configuration.
