Straight Talk About Scalding
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
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"
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
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
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."