The sample will be brought into suspension with demi-water. The sinking rate depends on the lower limit at which desliming is to take place. After this period the upper fluid will be pumped off and the procedure will be repeated (max 10 times) until the sample is 'clean'.
The use of a laboratory coat is compulsory. Check if the machine is clean.
The machine consists of an underside like a cooking pan (1)provided with, on its bottom, small obstacles connected to demi-water, on which a cylinder (2) is attached with a span band, and inside a suction tube (3) with stabilizer plates, which is connected to a pump(4). Furthermore, a panel with valves (5) and the main tap are on the wall, together with a processor controled switchbox (6) on the panal above the desliming machine. Under the table is a container with a 10% Calgon solution.
This version of the machine is an automatically operated system and consist of 4 desliming units which can be used independendly, controled by another controlbox.
PRINCIPLE OF DESLIMING
The working of the machine is based on Stokes' Law:
V = speed of particle, cm/sec
ds & df = density of particle and fluid g/cm3
b = viscosity of liquid, poise
g = gravital accelaration cm/sec2
r = radius of particle, cm.
The speed with which a particle sinks in a liquid is proportional to the radius of this particle. After some time (t) all particles with radius (r) have travelled height (h) in a liquid. Consequently, the amount of time can be calculated for particles of a certain size to settle. When at that moment the upper liquid is drained, the liquid will contain only particles that are smaller than the size calculated.
The table below shows the settling times at a height of 40 cm of particles with variable granular size and density.
A period of 8 minutes should be observed for safe desliming.
- Desliming machine
- Calgon solution 10%
The machine is set up without the exhaust unit. The demi water tap on the wall is opened and the mainswitch (wall socket) turned on.
Subsequently, the sample (in the 0,4% Calgon solution) is washed in the cylinder. The suction tube (rocket) is placed inside the cylinder and lifted to the highest position and connected to the pump tube. The plug of the two floating waterlevel detectors must be connected to the controlbox. Attach the tube of the Calgon solution with a clip to the suction tube.
Press the enter button on the controlbox.
The display shows:
INSTALL ROCKET (suction tube)
The water level shall be filled up to detection on the suction tube
REM. TIME 15 MIN.
(after 15 min.)
WAIT ! PUMP EMPTY
After 15 minutes the upper part of the liquid is pumped away. Delay switching off until the pump pumps air (to prevent emptying by siphoning).
Move the suction tube down until it touches the sample. Mark the tube and then lift it 3 cm.
P1 : 8MIN
P2 : 7MIN
P3 : 6MIN
P1 : 8MIN
STEP 1 ADD SOAP
200ml Calgon 10% will be added.
REM. TIME 75 MIN
Filling the desliming machine
STEP 1 WAIT!
REM. TIME 74 MIN.
(after 8 minutes)
WAIT ! PUMP EMPTY
STEP 2 ADD SOAP
REM. TIME 66 MIN
This procedure will be repeated 10 times as long as the upper level of liquid is clear.
The last 2 times without adding Calgon anymore. After the last cleaning the upper liquid is pumped away, but no new input will take place.
The machine has to be taken apart. The suction tube is taken out of the cylinder, which in its turn is removed from the pan by releasing the span band. The deslimed sample is transferred with demi-water to a stainless steel bowl. Subsequently, it is poured off and placed into an oven of 50 C to dry.
Unscrew the bottom of the pan and clean all machine parts thoroughly for the next sample.
It is possible to stop the process at any time:
Press enter to stop.
WAIT ! PUMP EMPTY
The waterlevel is detected by two floats. The first one is to detect the right waterlevel, 40 cm above the suction nozzle, the second in case the first dectection refused, will stop the watersupply. A red light will be flashing on the controlbox together with a sound signal. Nevertheless the process continues normal. In case of an alarm you can stop the process by pressing the enter button. Don’t forget that after you confirm with YES the pump immediately starts pumping while settling of the sample wasn’t finished.
In case the second detection fails and the water runs over (overflows) you must push the red emergency button on the right site of the panel. The water supply will stop immediately.