How to cap pipe ends while sink disconnected

[bazak1]

Hi,
I have to disconnect the sink so i can remove and replace both sink and cabinet, but while its all out of the way theres a couple of jobs i need to do.
The bendable pipes with isolating valves is what i want fitted for when the sink is ready to be connected, but can i fit it now ( while the sink is out ) so i can turn the valve off but still turn water supply on, and if so can i be assured that it wont blow off or leak.

 

[Bahco]

Fit them properly with the pipe fitted fully into the fitting and some jointing paste, tighten them up right and all will be well.