Preventing contamination of pressure standards is very important. Contamination can lead to costly repair or even replacement of pressure standards. By far, the most frequent sources of contamination are test devices (also called test gauges, gauges, UUT or DUT). This article discusses methods of cleaning test devices.
See this article for discussion of contamination prevention and devices offered by Fluke Calibration, Contamination Prevention of Gas Operated Pressure Controllers / Calibrators
What is contamination? Contamination is anything that you don't want to get in your pressure standard. With a gas operated pressure controller contaminants can be water, oils, fuels, alcohol, other liquids and/or solids (particulates, dirt). Note that if a pressure gauge is normally used to monitor a water line it will be full of water. This isn't a contaminant when the gauge is in use, but it is a contaminant if you're going to calibrate the gauge with a gas operated pressure controller.
How to prevent contamination of a gas pressure controller?
* Clean the gauges before calibrating them
- Basic method
At it's most basic form, cleaning could be done by draining (as best possible) a gauge. An additional step could be filling the gauge with a cleaning liquid. Repeat both steps as necessary. A syringe with a long, thin, flexible tube might be helpful if the gauge has a large circular bourdon tube. Of if you have a bottle of Swagelok Snoop it probably has a long flexible tube. You could drain the bottle (or use an old one) to drain and fill gauges.
- Advanced vacuum method
The example setup below shows how to use vacuum to evacuate a gauge, fill it with a cleaning solvent and evacuate the solvent. Before applying a vacuum to a gauge make sure that the gauge can withstand the vacuum without being damaged.
What is needed?
- Vacuum pump. Could use a hand vacuum pump but likely not as effective
- Test connection
- Valve(s). A single 3-way valve is used in this example
- Cleaning solvent reservoir (reinforced model)
- Waste reservoir (reinforced model)
- Plumbing
Note that the reservoirs in this system are scientific flasks designed for use under vacuum (reinforced, especially the necks).
Photo of example system
Schematic of example system
Steps to clean a gauge.
- Connect gauge to the TEST port
- Switch valve so the VACUUM port is connected to the TEST port. The SOLVENT port is not connected.
- Turn on the vacuum pump. Note that liquid in the waste bottle might boil under low pressure and enter the vacuum pump. This is typically a small amount but be aware.
- If you don't want a deep vacuum then leave the stopper in the flask a bit loose or tee in a valve to regulate the vacuum
- When the gauge is evacuated as desired, switch the valve to OFF and turn off the vacuum pump
- With a compatible cleaning solvent (sometimes just water but often a cleaning alcohol) in the SOLVENT reservoir, and a good seal on the SOLVENT flask, switch the valve so the SOLVENT port is connected to the TEST port.
- The gauge will fill with solvent
- Repeat steps 2 to 7 until gauge is clean
- Repeat steps 2 to 4 to evacuate the final solvent fill
- Turn off the vacuum pump
- Disconnect the gauge
- Finished
Note that if you fill the solvent reservoir with a desired test fluid (or use a separate reservoir) you can use this same system to fill a gauge by stopping at step 6.
Gauge cleaning and contamination prevention can be effective at preventing contamination of pressure standards. For questions, contact Fluke Calibration Pressure Technical Support at the below link or by calling +1.877.355.3225.
Keep learning
Contamination: is this hidden hazard threatening your pressure lab? - Blog Post
Mixing fluids in a high-pressure calibration without fear of contamination - Blog Post
Equipment Tips for Pressure Controllers in the Production Process - Blog Post
6270A Contamination Prevention System - Video
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