Dear plumber forums, >>>>>BACKGROUND TO ISSUE>>>>>>>> Hello. I am a med student, who is a do it a big do it yourself-er and believes greatly in the freedom and autonomy a man has by being handy by knowing plumbing knowledge. Unfortunately, my family is anything but handy, in fact they discourage my handy-ness and desire to fix stuff(badgering me that I will break something-even though I have fixed sooo many things), moreover are too cheap to actually fix anything, or to invite a professional plumber to do a job. Now I am angry, and frustrated because I decided to get a new under mount sink installed, and..... >>>>>KEY ISSUE>>>>>>>> my shut off valves underneath the sink are leaking when shut them off. So I decided to replace them . I cut off a sample of my shut of valve and brought it to my local kitchen/bath plumbing store. A gentleman who said he is a plumber said that I have pex (shut off valve attached to a grey plastic pipe,held on by a copper compression ring). The plumbing store sold me a metal pex shut off valve, some whiteish plastic pipe, and copper rings .They also rented me a pex crimping tool (which looks like the biggest wrench I ever saw). Now I fit the copper ring on teh plastic pipe using a second very little plier, I opened the mouth of the plastic pipe a bit and fit it over the mouth of the copper t tube with the copper ring. BUT THE COPPER RING WOULD NOT FIT FULLY OVER THE PIPE OVER THE THE copper "T". I tried and tried to force the ring over the copper "T" , but it could not go easily, even though the pipe did. I tried crimping it as is, the valve held for 5 minutes, then exploded gushing out water...... what a disaster. My thinking tells me that the compression valve should have fit over, pipe and copper "T" joint without too much force before crimping it, but it did not want to fit over.....does this mean I need a bigger compression ring, or should I just call a plumber?? Angry frustrated med student who will never try to fix anything anymore.