How Does It Work? Shower Trims and the Valves Behind Them


Turning on the shower. It’s something you do every day, but do you ever think about how it works? And whether the handle in front of you has an effect on what is behind the wall?

This guide will walk you through everything you need to know about shower trims, valves, and how showers work. We hope it will answer any questions you may have, and send you on the right track for your shower renovation or installation.

The Shower Trim

The handle to turn the shower on and off and the ring of metal that surrounds that handle are collectively known as the shower trim. The shower trim not only turns the water on and off, but also adjusts the water temperature, and can control the water pressure in some instances.

As you shop for a shower trim, you may notice that the market is dominated by single handled shower trims. This is because many states do not allow dual-handled trims, where one handle or knob only controls the hot water and another handle only controls the cold water. Scalding burns can occur when the hot water handle is turned all the way on and the cold is completely off. A single handle shower trim prevents scalding burns, as even at its highest heat setting, some cold water is combined with the hot water. We also recommend lowering your hot water heater to 120 degrees to prevent burns.

Shower trims come in several styles and finishes, and often have matching showerheads available as well. When the shower trim and showerhead are sold together, the sets are known as Shower Faucets. When tub filler faucets are sold with shower trims and showerheads, the sets are known as Tub and Shower Faucets.


Shower Diverters

Showers with multiple showerheads and body sprays use diverters to control which fixture is using the water when. Shower diverters are small handles that move the water from one fixture to another. Most diverters do not turn the water on or off in the shower, however, as that job belongs to the shower trim. Some shower trims, like Hansgrohe’s Thermostatic Trim with Volume Control and Diverter, combine the shower trim and diverter into one unit.

Diverter Valves

Diverter valves sit behind the wall near the shower trim. Diverters are typically set in a default to push water up to the showerhead, but can be adjusted to push water through a tub filler faucet, handshower, or body sprays. Most tub filler faucets automatically have a diverter included. Diverters for body jets must be added, and require a shower diverter handle on the outside of the wall.



Behind the wall of the shower, connecting the shower trim and diverters to water pipes, are faucet valves. Valves control the temperature and amount of water flowing into your shower, and also turn your shower on and off.

It is very important to note that shower valves are brand specific. This means you can only use a shower trim from the same brand as your valve, and often a trim will only work with a specific valve. If you are renovating a bathroom and will not be replacing the valve, it is important to buy a trim to match your pre-existing valve. During a complete renovation or new bathroom build where a valve will be added or replaced, be sure your valve matches your trim. The spec sheet and product description of a shower trim will typically note the required valve. Occasionally valves are included with shower trims, but most are sold separately. 

Putting It All Together

How does a shower work? It’s easy! When the shower trim is turned on, water is pulled from your water main or well, gains pressure through your water meter, and is then split into two streams. The cold water stream is pushed directly to shower’s cold water stream while the hot water stream takes a trip through the water heater to get warm before it flows into the shower’s hot water stream. Both the hot and cold water stream meet behind the shower wall where the shower valve controls how much hot and how much cold water is needed. The water is pushed up into the showerhead or flows through whichever apparatus the diverter may guide it towards. When the shower is turned off, the water ceases to flow into the shower pipes.

Any Questions?

Understanding showers and the walls behind them can be difficult, even for professionals. If you ever have questions concerning a shower, give our team of product experts a call! These highly trained customer service agents know their stuff and can guide you toward the best fixtures and installation types for your unique situation. Call (877) 781-3114 to learn more.

Ready to take your shower knowledge to the next level? Shop the SUPPLY.com shower collection now!