There are basically three methods used to mount the angle stop valves. 1. Solder type 2. 1/2"NPT Thread mount 3. 5/8" compression mount. In new construction the angle stops are generally installed during the final trim out phase of the plumbing, which generally occurs after the painting or wall finishing phase. At this stage there is a very high risk of causing damage to the wall finish if we were to install the solder on type or to solder a thread adapter on the stub out. For this reason most plumbers elect to use the 5/8" compression type which only requires a simple mechanical connection. To install the compression type angle stops the stub out is cut to the desired length, then the compression nut is slide on the stub out, followed by the brass ferrule and finally the valve is slipped on. With the valve held firmly in its final location, the ferrule and compression nut is then slide out to the valve and tightened finger tight. Once the compression nut is finger tight the plumber uses two wrenches, one to hold the valve steady while the second wrench is used to tighten the compression nut. As the compression nut is tightened the inner brass ferrule is slightly compressed into the wall of the copper pipe thereby locking it firmly in place. When changing compression mount angle stops many people make the mistake of attempting to pull the ferrule and old nut off the copper stub out and usually in doing so they distort the shape of the copper making it very difficult to get a tight seal with the new nut and ferrule. A much simpler and more reliable method is to unscrew the compression nut then slide the old valve off the copper pipe leaving the original ferrule and compression nut on the pipe. You then remove the compression nut and ferrule from the new valve and slide the new valve on the pipe, tightening it in place with the original nut. While this method does not work 100% of the time, as a rule it will work most of the time and certainly bears trying before you begin cutting the pipe or trying to remove the old ferrule. When tightening the compression nut you can use a pair of channel locks to hold the valve steady, but when doing so be sure to pad the valve with a rag first so the teeth of the channel locks does not scratch the finish. I find an open end wrench to most convenient to tighten the nuts in a tight space. (I especially prefer my Craftsman ratcheting open end wrench.) When selecting angle stop valves I use the solid brass 1/4 turn ball valves exclusively. The ball valves have the advantage that they are quick acting full bore valves and they are also have the advantage that when turned they are self cleaning which is a distinct advantage in areas where mineral scale builds up on internal valve parts. I will probably open a real can of worms here, but My first choice of supply lines is chrome plated brass tubing with the cone washers that come supplied in your faucet set and the compression nut and ferrule that comes supplied with your new angle stops. I have seen copper or brass tubing supply lines that have been in continuous service in commercial applications for 20 or 30 years and they still work fine. My absolute last choice would be the stainless steel brain lines. While the stainless steel braid gives the illusion of being some kind of high tech space age strength and durability in the final analysis many of those lines are the absolute weakest link of all the choices. It is true that the stainless steel braid will prevent a line from blowing out, but when we consider that the maximum allowable line pressure is 85psig, the chances of any lines actually blowing out is slim to none. On the other hand, what most people don't know is that a vast majority of those stainless steel braid lines has nothing more than a stainless steel braid over a cheap neoprene hose. Under certain water conditions neoprene has a relatively short service life as is evidence by the failure rate of neoprene toilet flapper valves. In regions where they have problems with the water deteriorating the neoprene I prefer to use chrome plated brass lines with the factory preformed cone washers that are made out of nylon.

Quote;"I much prefer using ball valves in applications where they are to be in either the fully on or fully off position. In in-between positions, they tend to 'sing' (and I don't favor their taste in music)." Gate valves & ball valves are defined as "Full Bore Valves" and they should never be left partially closed. They are intended to be either fully open or fully closed at all times, no exceptions. Leaving a full bore valve partially closed can and will lead to a number of other problems on the line including an increased risk of pin-holes on the downstream side of the valve. I prefer ball valves for 3 reasons. 1. A ball valve is constructed of a round ball with a hole drilled through it equal to the diameter of the pipe. When the valve is open the interior of the valve is almost equal to the interior of the pipe so there is no associated turbulance or friction as the liquid flows through. 2.Generally the ball is suspended in a nylon or teflon bearing pad between the ball and the valve body that primarily serves as a seal but it also serves as a bearing to make turning the ball easier. 3. The handle should be attached so that it is in the same direction as the hole through the ball. When installed in that manner you have a good visual indicator of when the valve is open or closed. When the handle of the valve is parallel to the pipe, the valve is open, and when the handle is at right angle to the pipe, the valve is closed. It is almost impossible to look at a gate valve and tell if its open or closed, unless or course, you elect to use OS&Y(outside stem & yoke) gate valves, but I doubt if you will ever see an OS&Y gate valve in a residential structure because they are typically only used on lines that are 3" and greater, and OS&Y valves are extremely expensive.

Some valve bodies have an auto shut off feature which is designed to prevent scalding. If one side has no pressure, both sides are shut off inside the valve body. Or you dislodged some huge chunk of rust and it made its way to the shower valve. I can't see from here. Try dissembling the shower valve and flushing it out.

I recently installed a Delta single handle shower control, and the max setting for hot was accessible after removing the shower control trim. The piece that determines the max hot water position is is just two sets of toothed/geared wheels that fit together, and you can index them in either direction. This youtube video provides a good explanation of the hot setting for the Delta single handle controls. https://www.youtube.com/watch?v=n2_uZ7wgV1I My shower valve worked like the one shown at about 2:07 minutes into the video. Bruce