Making bathroom fixtures stylish and readily available means making sure the workhorse components, aka the shower valves, are doing their job distributing water correctly so you can experience an effective and most importantly a relaxing shower.
The workhorse behind a shower set is the valve, also known as the fitting. While many of us might not understand the parts inside and out as to how this piece of metal controls the water flow and temperature, we have taken a look and answered five of the most commonly asked installation questions regarding this valve to help with the ease of install. 
Before we dive into those five common installation questions, let's break down what a valve actually does.
What does a shower valve do?
A shower valve is generally made of solid brass, although you can find some models that are made from plastic components. The main job of the fitting, or valve, is to direct and control the flow and temperature of the water coming through your shower outlets. With a well manufactured and installed shower valve the fluctuation of water temperature and pressure when showering can be greatly reduced, thus enhancing the relaxing experience we all want in the shower.
Many factors may change the showering experience. For instance, if the valve is installed incorrectly, this will compromise the use of the shower.
How does a shower valve work?
Behind the Walls: How Does a Shower Work? - Quality Bath. Posted by Yael / Updated May 16, 2018
"So here’s how the shower valve works: you turn the trim, which pulls water from your water source. Cold water goes straight to the cold pipe, while hot water makes a stop in the water heater first. Water from both pipes meets at the shower valve, which mixes it together and sends it to the shower head or tub spout.
Depending on your shower configuration, you will need different types of valves and hardware. The trim must be compatible with the rough, so check brands for compatibility." Resource: Quality Bath.
Top 5 Installation Questions:
1.) How does the diverter share functions?
The top handle of the valve shown above controls the on/off and diverts the water between functions. It has 4 positions, the first being off. Every 90 degrees is a new function, starting at no water flow and gradually increasing to full flow once it 'clicks' into place at the 90-degree position.
2.) How do I set the temperature?
The bottom handle of the valve shown above controls only the temperature. It's a thermostatic mixer which means you find your ideal temperature then you can leave it there. Next time you come to use the shower, turn it on, and once the hot water reaches the valve it'll get to your preset temperature, no more of that wasted 5 minutes trying to find the perfect temperature! It also keeps the temperature consistent as long as there's a hot water flow (i.e. you don't run out of hot water). If a toilet is flushed or the dishwasher starts, the sudden change won't drop the water temperature as is common in nonthermostatic or pressure balance systems.
3.) The stems are too long, how do I cut them down?
In order to accommodate different wall thicknesses and keep a clean look, the stems come longer than needed and are cut down to the needed length once the finished wall is installed. Follow the instructions shown in the instruction manual to complete this step.
4.) Where should the valve be set in the wall?
Ideally, a 2"x6" wall is used with the F943-VO valve. This allows for a sturdier backer board to secure the valve to. If a 2"x4" wall is used, there's space for a 3/4" piece of plywood behind the shower valve, we'd also recommend using pipe straps to keep the valve secure over the years of use it will get.
5.) Why should I buy this valve?
The F943-VO gives you the functionality of a large custom setup in one compact valve. With a flow rate of up to 8 GPM, it allows you to control 3 different outlets in the same shower without compromising on style or function. The thermostatic function gives you the experience of a high-end, custom shower, at a fraction of the cost.
