Issue: 8/05

Much has been written lately about the potential of scalding associated with sink, shower and bathtub fixtures. And, viewpoints certainly vary. A balanced perspective will come from the American Society of Sanitary Engineering (ASSE), which is in the process of finalizing a comprehensive, integrated set of standards that segment and guide the various products by type and overall system design. The specifier's challenge today is in not looking at each individual valve, but considering the role each valve will play in the overall system design. To start, consider the chart in Figure 1, which delineates the various types of ASSE-compliant valves that may be needed in differing applications throughout a single system.

The water heater is set at the maximum temperature needed, which for the purposes of our example will be 140

Figure 1. Various ASSE-compliant valves may be needed in a single system. (Courtesy of Symmons Industries.)
With that established, it becomes helpful to understand the differences between thermostatic and pressure-balancing valves used to mitigate downstream scald potential in ASSE 1016 installations. ASSE 1016 devices for showers, in particular, require the ability to have bathers protected from a sudden temperature change resulting from a disturbance in the cold water supply pressure. Sudden increases in outlet water temperatures up to the maximum available hot water temperature can result in scalding and/or slip and fall accidents, as bathers recoil from the heat and try to flee the shower area. Both types of scald-resistant valves have specific strong points that should be leveraged in an overall system design.

Consider the following objective test sequence: When water temperature changes resulted from a sudden pressure disturbance similar to a toilet flushing while an adjacent shower is in use, the performance of a variety of different safety and non-safety shower valves were monitored and tracked. The showerhead is a standard, commonly used model, as is the standard water closet flush valve. Structured in this manner, the test was more "real-world"

Figure 2. The results of Test 1 show how the water temperature in the shower is impacted when a non-safety shower valve is used.
Figure 2 shows how the water temperature in the shower is impacted when a non-safety shower valve is used.

In Test 1, using a conventional, single-handle, non-safety shower valve with no flow restrictor, the shower outlet water temperature spikes to over 130

Figure 3. This temperature/time curve compares a non-safety valve with a 2.5-gpm flow restrictor to a thermostatically controlled shower valve at full flow (+6 gpm).
In Test 2, although better than a non-safety valve, the thermostatic control valve still shows a significant temperature spike to over 110

Figure 4. Test 3 tracks the reaction of the thermostatic valve with a federally mandated 2.5-gpm flow restrictor to a sudden loss of cold water pressure.
Now, let's examine how adding a 2.5 gpm flow restrictor impacts the thermostatically controlled valve's performance. Figure 4 tracks the reaction of the thermostatic valve-with a federally mandated 2.5 gpm flow restrictor-to that same sudden loss of cold water pressure (toilet flushing).

In Test 3, note that the slower reaction of the thermal motor, caused by the restrictor, results in a maximum outlet temperature of over 120

Figure 5. The instant a pressure disturbance occurs, the pressure-balancing valve adjusts, providing a predictable, constant temperature reading throughout the test sequence.
If we run the same toilet valve flush test once again, but now add a pressure-balancing safety valve with a flow restrictor, the results are vastly different (Figure 5).

This time there is virtually no measurable temperature change at the shower outlet. That's because the operating dynamics of the pressure-balancing valve provides "instant response."