Nope. The plastic cap won't keep air in the tube; they don't seal tight enough, and if the valve is open, the cap will just push down on it and make it leak faster.

The only use I have for a presta cap is as an emergency shraeder adapter. Cut off the tip, turn it upside down, and screw it on. You can then use a shraeder pump or gas station compressor.






https://www.purecycles.com/blogs/bic...hrader-adapter