Before using the extractor system as a multi-stage process users may find it useful to operate the three solvent stages independently from the rest of the system, this will allow the user to master the techniques that will be needed to keep the three stages running in balance. It is important to balance the stages since they cascade from one to another. If one stage pump is running too fast relative to the other pumps there will be a tendency for the trough which is supplying the pump to run dry and for the next trough down the line to over flow. Out of balance running can lead to instability and intermittent liquid flows can cause the heater protection circuits to operate.
Note: For correcty operation the first and second stage troughs must not be allowed
to run dry and the level must not be allowed to rise so that the elbow on the vent pipe (mounted through the side wall of each trough) becomes submerged.
The objective of the following method is to fill the stage troughs to a depth of
approximately 15 mm of water and to set the stage pumps running so that the three stages run in balance at the desired operating speed:
1. Check that the mains switch (15) on the front of the console is in the off position.
2. Check that all of the rotary controls (16, 17, 19a, 19b & 19c) on the console are set to zero (fully anti-clockwise).
3. Check that all three of the heaters are switched OFF using the switches (20a, 20b & 20c) on the front of the console.
4. Switch the on the mains power using the mains switch (15) on the front of the console.
5. Switch the RCD/RCCB (23) and circuit breakers (24a, 24b, 24c & 24d) on the back of the console to the on position.
6. Fill the fresh solvent tank (11) with clean water.
7. To save time, fill solvent collection trough one (8a) and solvent collection trough two (8b) to a depth of approximately 20 mm by pouring water in through the rotor.
8. Pour water into the third stage trough (8c) until the water level reaches the point where it drains into the final miscella tank (13). Note that the final trough will drain completely.
Operation
9. Prime each of the pumps (3a, 3b & 3c) in turn by setting the appropriate speed control (19a, 19b or 19c) to maximum until water exits the appropriate sprinkler bar (6a, 6b or 6c).
10. Once the system has been primed the three pumps can be adjusted to run at the desired rate (eg. setting 5.0 on the potentiometer for half of maximum flow). Water from the fresh solvent tank should now be cascading through the three stages via the three pumps and troughs and then draining into the final miscella tank.
11. After the system has been running for a while the levels in solvent collection troughs one and two will indicate how well the flowrates in the system are balanced. If the system is perfectly in balance then the levels in troughs one and two will not have changed, however if the levels are changing an
alteration to the system will be needed. To make the necessary changes the following steps can be followed:
12. Use the flow rate of pump 1 as the master setting for all of the solvent flows by leaving the speed control (19a) fixed at the desired rate. The user will find that this technique will greatly reduce any complexity involved in balancing the system since it can now be balanced using alterations to the two other pumps only.
13. Having set pump 1, work from right to left through the solvent stages when making changes ie. first look at the trend/level in trough 1 (8a) and alter the speed setting (19b) of pump 2 to change the trend. If the level in trough 1 is falling reduce the speed of pump 2. Conversely, if the level in trough 1 is rising increase the speed of pump 2. If the level has changed substantially from the half full position temporarily set the speed to maximum or minimum as appropriate then reset the speed to normal when the level has been returned to half full. Note the change in pump speed necessary to restore the balance.
14. Once pump 2 has been set to maintain the level in trough 1 the user can look at trough 2 (8b). The control of the level in trough 2 is slightly different to that in trough 1 since trough 2 has a variable flow of liquid into it (controlled by pump 2) as well as a variable flow of liquid being removed from it (controlled by pump 3). When the user adjusts the speed of pump 3 to maintain the level in trough 2 it will be necessary to consider the effect of any changes that have been made to the speed of pump 2 as well as any existing change in the level. If for example trough 2 was maintaining its level before an increase in pump 2 speed, it will be necessary to increase the speed of pump 3 by a similar amount in order to compensate for the increased flow into the trough from pump 2 .
15. The level in the final trough (8c) does not require any adjustment since this is self-controlling.
The balancing procedure described above should be repeated as frequently as is required. Users will find that as the balance becomes more precise, the period between speed adjustments will become longer and the required adjustments will become finer. Maintaining the balance will be easier if trends in the liquid levels are spotted early and small adjustments are made to the flows to compensate.
Once the user has balanced the system it is possible to retain the approximate pump settings for future use by making a note of the potentiometer settings (19a, 19b & 19c).