| 摘要 |
<p>In one aspect, the prevent invention provides control apparatus for controlling the pressure of a water distribution system. Typically the apparatus will be connected to a main pressure reducing valve in the system, which main valve is under the control of a dual diaphragm pilot valve. The control apparatus includes variable gas pressure output pipes which, in one embodiment, are connected to the pilot valve. There is also provided a relatively high gas pressure source and a relatively low gas pressure source, each of which are selectively connectable to the variable gas pressure output means in order to vary the pressure of the variable gas pressure source.</p> |
