PRESSURE REDUCING VALVES / STATION


 

pressure reducing valves / station

Pressure-Reducing Valves

Pressure reducing valve - Depending on the system requirements this can be either-

          Pilot operated valves, Direct acting valves or pneumatically actuated valves.

Steam, liquids and gases usually flow at high pressure to the points of final use. At these points, a PRV lowers the pressure for safety and efficiency, and to match the requirements of the application. There are three types of pressure-reducing valves.

Direct-acting

The simplest of PRVs, the direct-acting type, operates with either a flat diaphragm or convoluted bellows. Since it is self-contained, it does not need an external sensing line downstream to operate. It is the smallest and most economical of the three types and is designed for low to moderate flows. Accuracy of direct-acting PRV is typically +/- 10% of the downstream set point

Internally piloted piston-operated

This type of PRV incorporates two valves-a pilot and main valve-in one unit. The pilot valve has a design similar to that of the direct-acting valve. The discharge from the pilot valve acts on top of a piston, which opens the main valve. This design makes use of inlet pressure in opening a large main valve than could otherwise be opened directly. As a result, there is greater capacity per line size and greater accuracy (+/- 5%) than with the direct-acting valve. As with direct-acting valves, the pressure is sensed internally, eliminating the need for an external sensing line

Externally piloted

In this type, double diaphragms replace the piston operator of the internally piloted design. This increased diaphragm area can open a large main valve, allowing a greater capacity per line size than the internally piloted valve. In addition, the diaphragms are more sensitive to pressure changes, and that means accuracy of +/- 1%. This greater accuracy is due to the location, external to the valve, of the sensing line, where there is less turbulence.

This valve also offers the flexibility to use different types of pilot valves (i.e., pressure, temperature, air- loaded, solenoid or combinations).

Separator

This removes water particles and entrained moisture eradicating erosion, corrosion, and water hammer, and maximizing the heat transfer capability of downstream equipment.

A separator is a body in the pipeline which contains a series of plates or baffles which interrupt the path of the steam. The steam hits the plates, and any drops of moisture in the steam collect on them, before draining from the bottom of the separator.

Downstream pressure gauge - This monitors the status of the downstream pressure.

DownstreaM stop valve

This allows any downstream equipment to be double isolated during maintenance periods. It also allows the pressure reducing valve to be correctly adjusted during commissioning by isolating the flow.

Upstream stop valve

This allows the station to be shut down, and is positioned after the separator so that the condensate cannot build-up in the supply line during this period.

Strainer- Strainers arrest any dirt before it is able to pass into the pressure reducing valve.

Upstream pressure gauge-This monitors the status of the supply pressure.

Safety valve-This is required to ensure the downstream pressure can never rise above the maximum allowable pressure of any equipment in the down stream pipe line

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