Excessively hot samples can cause damage to expensive and sensitive hardware and electronics. For process analyzers and similar instrumentation, it is important to assure that the process samples fluids are always below the maximum allowable temperature for such instruments.
The HST (High Sample Temperature), HAT (Heat Actuated Trap), or TV/HAT (Tube Valve Heat Actuated Trap) can be used as a sampling system safety shutoff to protect downstream analyzers, instruments and personnel from high temperature damage. The valve will remain open as long as sample temperatures are under the setpoint of the valve. If the sample temperature increases, the valve will shut off, protecting analyzing equipment or personnel. The HST is rated for 3000 PSIG (207 BAR) which makes it ideal for high pressure applications.
The HAT and TV/HAT valves are also used as scald protection valves on commercial aircraft. In commercial airplane galleys, upset conditions can cause boiling water to unexpectedly flow from the coffee maker to the faucet. The HAT or TV/HAT is installed on the water line to the faucet to sense the water temperature and close off when excessive temperatures are detected, preventing scalding of passengers and crew.