REGULATING VALVE APPLICATIONS PRESSURE REDUCING STATION • Using Spring-Loaded Pilot
PURPOSE:
For reducing system inlet pressure to a constant outlet pressure.
OPERATION:
The pressure reducing valve (PRV) can be easily adjusted to set the desired outlet pressure and modulates to maintain that pressure setting. The PRV requires no external power source.
INSTALLATION GUIDELINES:
(see Figure 5)
• This example depicts a pilot-operated steam PRV, whereby an external sensing line is required to sense downstream pressure. The end of the sensing line is placed away from the turbulent flow of the valve outlet. This helps to improve accuracy of the set pressure. Set pressure is adjusted by turning a screw on the pilot to increase or decrease compression on a balancing spring. • For optimum operation and service life, maintain recommended minimum piping straight runs before and after the PRV. Inlet pipe diameters could be 1-2 sizes larger and outlet pipe diameters 2-3 sizes larger than the end connections of an appropriately sized PRV. The purpose of increasing the pipe size downstream of the regulator is to keep the steam velocity constant on both sides of the regulator. • The pressure sensing line should slope downwards, away from the regulator, to prevent condensate from entering the pilot. • 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 the separator shown upstream is appropriate for protection of the PRV, it is not always required as a properly sized drip leg with steam trap may 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 installing a properly sized bypass line with globe valve to provide continuous operation should regulator maintenance be required. • Consider low-cracking pressure (1/4 PSI opening pressure) check valves after steam traps when discharging into condensate return lines. Check valves eliminate the possibility of condensate backing up through the steam trap into the system. • A safety relief valve (SRV) is appropriate where applicable codes dictate their requirement, or anywhere protection of downstream piping and equipment from over-pressurization is desired. The SRV needs to handle the complete volume of steam from the regulator and bypass loop. Consult the factory for appropriate SRV sizing guidelines. • Orifice plates help reduce pipeline noise and are available as needed. Series OP orifice plates are custom engineered to maximize noise attenuation and reduce dbA to the lowest achievable value. The number and diameter of holes will be determined based on application conditions, and the plate diameter will typically be equal to the recommended downstream pipe size. The regulator(s) must be sized in conjunction with the orifice plate. For PRV and orifice plate sizing, consult the factory or SteamWorx sizing program on www.watsonmcdaniel.com.
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www.watsonmcdaniel.com •• Pottstown PA • USA • Tel: 610-495-5131
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