REGULATING VALVE APPLICATIONS TEMPERATURE CONTROL of a SEMI-INSTANTANEOUS HEATER using a Pilot-Operated Temperature Regulating Valve
PURPOSE:
For accurate control of the temperature of a product being heated when the benefits of a pilot-operated regulator are required.
OPERATION:
A pilot-operated HD valve with PTRP temperature control pilot and PS solenoid pilot offers response times and characteristics suitable for semi-instantaneous heating applications. The temperature sensing bulb senses the temperature of the liquid being heated and allows modulation of the valve for appropriate supply of steam. The solenoid valve (PS-pilot) can be used to electronically activate on-off control of the heating process.
INSTALLATION GUIDELINES:
(see Figure14)
• Care should be given to the installation of the temperature sensing bulb to ensure full immersion in the liquid. The sensing bulb should be placed as close as possible to the heater tank to ensure accurate temperature control of the process fluid. • Eccentric reducers, if required, are used on valve inlets to prevent accumulation of condensate which could become entrained with high-velocity steam, possibly resulting in dangerous waterhammer. • While a separator is appropriate for protection of the Regulator, it is not always required, as a properly sized drip leg with steam trap may be sufficient. It is recommended for systems where steam is known to be “wet” and the entrained moisture could affect valve performance and/or result in component damage. • Consider low-cracking pressure (1/4 PSI opening pressure) check valves after steam traps when discharging intocondensate return lines. Check valves eliminate the possibility of condensate backing up through the steam trap into the system. • A vacuum breaker and auxiliary air vent (not shown) should be properly installed to promote proper drainage and optimum heat transfer. The vacuum breaker allows system equalization with atmospheric air to allow gravity condensate drainage when vacuum is formed from condensing steam. The air vent improves heat-up times and overall heat transfer by expelling accumulated air on start-up. • A safety relief valve (SRV, not shown) is appropriate where applicable codes dictate their requirement, or anywhere protection of downstream piping and equipment from over-pressurization is desired. Consult the factory for appropriate SRV sizing guidelines. • Semi-instantaneous water heaters with pilot-operated temperature control valves are often used in conjunction with a storage tank or mixing station for optimum temperature control of the process fluid.
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