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3 Cards in this Set
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Explain compound gauge |
Compound gauges are usually diaphragm-type gauges. A diaphragm gauge has a flexible diaphragm connected by a rocker bar and associated mechanisms which magnify the movement to a pointer (see Figure below). As you look at the face of the diaphragm gauge, you will notice it has a long vacuum scale and a short pressure scale. The scale on the vacuum side typically measures zero to negative 100 kPa (1.00 x 100 kPa). This allows for more accuracy over a small range of vacuum readings. (See Figure) When a positive pressure is applied, (from water supplied from a hydrant or another appliance) a small area of the diaphragm moves towards the small cavity in the front housing, thus giving a reading on the smaller area of the gauge. On the other hand, if a negative (below atmospheric) pressure is applied, a large area of the diaphragm shifts in the opposite direction within the larger cavity of the rear housing, which magnifies the negative pressure reading. |
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Notes |
Compound gauge measures both positive and negative pressure. Measures the pressures at the inlet side of pump. Negative pressure is shown when drawing from static water supply 1 metre of vertical lift is - 0.1 bar Positive pressure is shown when water supplied from a hydrant or another pump For example if 5 bar is supplied from hydrant , 5 bar will be shown on positive pressure side when valves are closed. |
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