Is there any reason why I shouldn't put the cover on before blowing lines?

[nikon5400]

I may need a new compressor and I may have access to mighty vac a few weeks later, so I figured if I put the cover on now I'll have a couple months to blow the lines. It shouldn't be a big deal to lift cover when blowing returns.

As for main drain -

Does jandy valve really keep main drain air tight?

I'm not sure how important to have it blown when pool water is 1-3" below skimmer (in-ground pool), but with 33gal compressor only the closer md bubbles, mighty vac does a lot better job

Thanks

 

[samt]

I always put my cover on before I blow the lines and pull the pump. I put the cover on run the pump until the water temp is below 60, I put one of those rubber plugs in the pipe after I pull the pump. So far, good air lock. I don't trust just the valve to hold an airlock.