How to Use a PTFE Stopcock in Aggressive Liquid Applications

PTFE Stopcock Valve

PTFE Stopcock Valves are a type of manual valve that function in a similar way as a ball valve. The body, stem and ports of the stopcock are made from polytetrafluoroethylene, commonly known as PTFE or Teflon®, an inert, durable, sintered polymer that is resistant to corrosive media, which makes it ideal for aggressive liquid applications. Here is how to use them:

For use in laboratory environments, PTFE Stopcocks work well as manual shutoff valves for glassware such as burettes, columns, flasks, and separatory funnels. They are simple for engineers and mechanics to install into existing systems and easy to use since they are manual-type valves.

Stopcocks are used in a variety of industries, including pharmaceuticals (example: Peracetic Acid – commonly used for sterilization), bio-medical (example: chemotherapy – incredibly corrosive in its early state), and food processing (example: beef and chicken processing plants sterilize by running acid through their systems to decontaminate), as well as, the aerospace and semiconductor industries.

The PTFE Stopcock Valves can be configured as traditional 2-Way on/off manual shutoff valves or 3-Way flow directional valves. The use of 3-Way PTFE Stopcocks allows the user to redirect a common flow to either an A or B outlet tank. Among other reasons, the 3-Way Stopcock application may be an A/B Sampling protocol or Extraction/Separation protocol, both of which are simplified with one 3-Way rather than two 2-Way valves.

Aside from PTFE, there are a variety of other fluoropolymer compositions useful for aggressive liquid applications, including PFA (perfluoroalkoxy alkane), PVDF (polyvinylidene fluoride), and PEEK (polyether ether ketone). These all differ in hardness, permeability, and transparency, and some engineers use blends of these as base materials, but PTFE has the best temperature range and can handle the most aggressive of chemicals due to its inert quality, even under the harshest conditions.

PTFE Stopcocks should only be used in low pressure applications. Pressure Ratings for PTFE Stopcocks vary based on size and style, but are typically rated at or below 80 psi. When high pressure service is required, a better option will be PVDF and even PEEK. However, the tradeoff is slightly lower corrosion resistance and high purity performance.

PTFE, in general, is considered a soft plastic and will damage easily. Flowing slurry mixtures with hard suspended particulates may become an issue for PTFE Stopcocks. Over time the suspended particles will damage the PTFE sealing surfaces and result in leakage.

However, a PTFE Stopcock can still be a better alternative than glass stopcocks since they don’t streak and you don’t have to use grease, which makes them easier to clean and makes for a better vacuum. No grease also means you won’t contaminate any mixtures, which is important for liquid applications.

Manipulating a stopcock is simple. When the handle points in the direction of flow, the valve is fully open. When the handle points perpendicular to the direction of flow, the valve is fully closed. At the 45-degree position the valve is halfway open and thereby has a metering effect on the media flow.

While Teflon does not require lubrication, it will thermally expand and contract with large swings in the valve body temperature. In turn, this will affect the torque required to rotate the valve stem (open/close the valve). Therefore, application temperature range is one of the key parameters in selecting the correct PTFE Stopcock. Other critical parameters include system pressure range, fluidic media, and the port connection type.

Care must be taken to remove the valve after a test protocol: 1) wear all required PPE protective gear, 2) thoroughly rinse the PTFE Stopcock with an appropriate neutralizing agent to remove contamination from the application media, 3) never force the stopcock, and always properly vent the system to remove stored pressure (energy), if the stopcock seems stuck to a flask or fittings try lowering the body temperature with ice, 4) once removed clean the valve as necessary using the local laboratory specifications.

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