Adding speed fit shut off tap to existing pipe

[homeowner27]

Hi
We are basically revenovating our bathroom so the eectric shower need to come off the wall.
My dad whos the one doing the work has hypertension and has a pace maker so I shouldn't be making him do such work. Today he already feeling unwell because of he's been over working.

I dont have any experience in plumbing but I am electrical improver so I like to think I can do this myself. Plus if you dont try you will never learn. other diyers would of obbtained their experience by doing it.

I want add a shut off valve to the supply for the shower because the flaming electrician that fitted the shower didn't think to add, on.
He added a shutoff valve that goes that open on the other side. I can only think he used it to as drain off so why didn't he add shut off valve to the shower.

this is what i am trying to archive.
How much does the speed fit pipe sit into the fitting?
My understanding is if i just cut a length of pipe to diamensions of the red arrow it would be too short.

 

[yorksbuilder]

Use the stars printed on the side of speedfit pipe to see how far they should insert into the fitting.
Dont forget pipe inserts

see below link:

https://www.plumbworld.co.uk/documents/john-guest-speedfit-plumbing-connection-data-sheet.pdf

 

[Madrab]

Yes, It would, pushfit fittings normally have a line as to how far the pipe will insert into it as well as the pipe will be marked. Alternatively the body will change diameter so it'll pretty apparent how far the pipe will insert into the fitting.

 

[homeowner27]

The one thing I thank the electrician for is he left quite alot of slack in the pipe. So i didn't have to measure anything.
it's roughly length of my forearm worth of slack!!

Ok the stop valve from was quite expensive 6 quid but I choose it because it was tooless operation. Also it didn't has any depth markings on it.