By Peter Telle
Pressure Reducing Valve
Pressure reducing stations have become the norm for the deep mining industry. There are many different designs, with varying levels of safety, as required by the pressures involved, and the needs of the mining engineers. Alongside safety, a continuous water supply, without interruptions, is essential, as these stations are often on critical supply lines to the mining areas.
AFC are able to assist the mining engineer with complete reticulation design of underground (and above ground) water supply systems. The designs consider safety, continuation of supply, and performing water hammer analysis, if required.
Basic Pressure Reducing valve
In its most basic form, this is a single valve designed to reduce a high inlet pressure to a lower downstream pressure.
AFC have products for this as follows:
A200 Pilot operated Pressure Reducing valve
This valve is available in 10 bar, 16 bar and 25 bar ratings, and sizes from 50mm to 1000mm. This valve will keep a constant downstream pressure, irrespective of varying upstream pressure or varying flow rate. The AFC Valve can handle pressure drops of up to 4:1 without cavitation.
Pressure Relief Valve
It is recommended to install a A500 Pressure Relief Valve downstream of every pressure reducing valve for the following reasons:
● Pilot operated pressure reducing valves react as water is bled in and out of a control chamber to close and open the valve. If downstream demand is reduced too quickly (by fast closing of an isolating valve), the pilot operated valve may react too slowly, thereby allowing the downstream pressure to momentarily rise above the required setpoint. The relief valve would react to this, and open to keep the pressure at, say, 1bar above the setting.
● Any foreign dirt particles in the pressure reducing valve may prevent its closure during demand shutdown. The relief valve will blow off to maintain the downstream pressure within required limits
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