In sampling systems, sample coolers are commonly used to reduce sample temperatures to the acceptable limits. The HST (High Sample Temperature) safety shutoff valve is used as a fail-safe to sense the sample temperature after the sample cooler. In the event of a loss of cooling fluid to the sample cooler, or if the desired sample temperature is exceeded for any reason, the HST valve will close to prevent damage to expensive analyzers and other equipment.
The reverse acting US/S-XR (Ultra Sense Control Valve) or TV/US-XR (Tube Valve/Ultra Sense Control Valve) can be used to control the flow of air or water used to cool the sample. By sensing the sample temperature out of the sample cooler and controlling the flow of cooling fluid into the sample cooler, the valve is able to maintain a more constant sample temperature. This could be important if the analyzer or other instrumentation requires that the sample be in a specific temperature range for proper analysis.