How do I properly size Emergency Thermostatic Mixing Valves?
There are several factors to consider before getting started. First, you must determine the manufacturer’s flow rate for each type of fixture. (The ANSI Z358.1 minimums are .4 GPM @30 PSI for eyewashes, 3 GPM @ 30 PSI for eye/face washes and 20 GPM @ 30 PSI for drench showers. However, manufacturers’ flow rates may vary.) Second, figure out the pressure available in your building, taking into consideration that long runs of pipes add to pressure drop. Contact the valve manufacturer for specific pressure drop information. Now, total up your fixtures and multiply them by their actual flow rates. For example: 3 eye wash stations 3.0 GPM @ 30 PSI (actual flow) 9 GPM 4 eye/face washes 3.5 GPM @ 30 PSI (actual flow) 14 GPM 23 GPM Total Output @ 30 PSI You would need a valve that would provide a minimum of 23 GPM total output to accurately supply tepid water to all fixtures if they were used simultaneously.
