Introduction to an EXAMPLE Fresh Water System
Water is pumped from the fresh water well to the camp tank which provides pressure and storage capacity for the camp.
The camp distribution system is located between the well and the camp tank, such that the pipe between the camp and the tank may have flow in either direction. All the pipes from the well to the camp tank, including in the camp area, are heat traced and insulated for frost protection.
Water is pumped by the booster pumps from the camp tank to the plant tank. This pipeline is insulated but not heat traced, and it is automatically drained into the camp tank when the pumps are shut off in cold weather. Between the booster pumps and the plant tank there is a branch pipe which runs to the AGB mine sump. From the plant tank, water is gravity fed to the plant and the AGB mine portal.
Both tanks contain a fire water reserve which can only be used when the fire valve is opened by a fire alarm.
Detailed Process Description and Control of Well Pumphouse
The well pumps are controlled by the high and low level switches on the 50,000 USgal camp tank, the pump pressure control valves and the hand switches. In automatic, relay logic alternately selects each pump on a call for fill. One pump operates, while one is on standby; the pumps are automatically alternated at each start up. The Hand/Off/Auto switch controlling both pumps must be in the AUTO mode for the pumps to operate automatically. On a start at low tank level, the selected pump starts and its pressure control valve begins to open simultaneously. when the tank is full, the high level switch closes the pressure control valve; when the limit switch on the valve stem closes, indicating a closed valve, the pump stops. The next time the low level switch opens, the other pump and valve will operate identically. Note that these particular pumps must be started against pressure. The pressure control valves also regulate downstream pressure, and have built-in check valves.
There is a pump selector switch which allows the selection of either pump when the Hand/Off/Auto switch is in hand.
The air relief valves exhaust any air present in the pump column on start up. A third air relief valve (not numbered) exhausts air present in the discharge header pipe.
The pressure relief valve on the discharge header opens on a high or low pressure surge, to prevent water hammer damage to the pipe. The HDPE pipe is rated for 200 psi, only 15 psi higher than the design pressure. This valve must be connected, and the shut off valve open, when operating the pumps.
Camp Tank
The tank is equipped with level switches as follows: high and low level switches, for controlling the well pumps; high and low alarms; which alarm at the mill control panel when the water level in the camp tank is outside the normal operating range, and a pressure gauge, which gives a local indication of the water level in the camp tank.
The fire water reserve becomes available when the camp fire alarm is triggered, which opens the solenoid valve. The solenoid valve also fails open in the event of a power failure. Note that the butterfly valve between the fire valve and the tank must always be open. The fire alarm also disables the booster pumps so that no water is pumped during a fire.
Fresh Water Booster Pump
The booster pumps are controlled by the plant tank high and low level switches and the pump control valves in the same manner as for the well pumps. Note that the pump control valves do not have a pressure regulating feature. Also note that the controls for the system are in the PLC, rather than using relay logic. The booster pumps are each equipped with a Hand/Off/Auto switch which must be in Auto for the pumps to operate automatically.
The pressure relief valve opens on a high pressure surge to prevent water hammer damage. This valve must be connected, and the shutoff valve open, when there is flow in the system.
In cold weather, the pipeline is drained. When both booster pumps are switched off, the temperature switch timer is started. When the low temperature switch has indicated a temperature lower than 0°C for 1-1/2 hours, the drain valve is opened. The drain valve can also be controlled by the Hand/Off/Auto switch, which must be in the AUTO position for the system to function automatically. The discharge pipe is heat traced for a short distance up the hill, as it will only drain to the point where it is level with the water surface in the tank.
Plant Tank
The plant tank is equipped with high and low level switches which are identical in function to the camp tank level switches, and high and low level alarm switches, which trigger alarms on the mill control panel when the water level is outside the normal operating range.
On the inlet of the tank, there is a locally mounted flow meter.
The fire solenoid valve is controlled by the plant fire alarm in the same way is controlled by the camp fire alarm. The fire solenoid valve also fails open in the event of a power failure. Note that the butterfly valve between the fire valve and the tank must always be open.
The discharge pipes to the plant and the AGB mine portal are insulated and heat traced. The pipe to the plant is equipped with an air and vacuum relief valve which allows air to flow in or out as the pipe empties or fills with water. The shut off valve should always be open.
Startup and Shutdown Proceeding and Preparation for Start UP
- Ensure there is adequate water in the well. The pumps must not be operated unless there is a steady state (after drawdown) water level at least one metre above overhead wires.
- Walk the pipelines to check for damage to the pipes or overhead wires.
- Ensure the camp tank and the plant tank level switches and alarms are operational.
- Ensure the camp fire alarm system, is operational, and the camp tank fire valve is closed.
- Ensure the plant fire alarm system is operational, and the plant tank fire valve is closed.
- Ensure the booster pumphouse PLC is operational.
- Ensure the booster pumphouse temperature switch is operational.
- Ensure all air/vacuum release valves, pressure relief valves and pressure gauges are operational, and their isolating valves open.
- Ensure all pump control valves are operational.
- Ensure all pump and pipeline isolating valves are open.
- Ensure the booster pumphouse drain valve is closed.
- Ensure the heat tracing systems are operational.
Well Pump Start up
- Select well pump Hand/Off/Auto switch for AUTO.
Booster Pump start up
- Select booster pump hand switches for AUTO.
- Select FCV-803 hand switch for AUTO.
Well Pump Shut down
- Select well pump hand switches for OFF.
Booster Pump Shut down
- Select booster pump hand switches for OFF.
- Select hand switch for HAND, and open valve.