PUMPS
pumps . Piston diaphragm pumps are designed near 60 strokes per minute or less .
“ Maintenance of centrifugal slurry pumps may turn out to be considerable as compared with positive displacement pumps which require maintenance on an annual or semi-annual basis .
“ Efficiencies of positive displacement pumps may run as high as 90 %. Centrifugal pumps have a peak efficiency at their best efficiency point but actual efficiencies may be considerably lower .
“ Centrifugal pumps are the industry standard for pumping gland seal water to the large centrifugal pumps on tailings service , ball mill discharge , or other duties . A steady flow is vital to the service life of these large centrifugal pumps even as pressures vary due to gland wear , head tank level changes or other causes . “ A positive displacement pump although more costly initially provides a steady flow of water to the gland seals . Variations in head tank level or condition of the gland area do not change the flow . The positive displacement piston pump provides a constant flow for a given strokes per minute .
“ Feed pumps for plate and frame filter presses operate over a range of capacity and pressure . Generally , slurry is initially fed to the press at a high feed rate . As the press fills , the pressure builds up and the feed rate is reduced in steps as the pressure recommended for the press is attained . Feed material may continue to pack into the press for a short time and then the cycle is ended . The pump is stopped . The press is emptied and the cycle repeated .
“ Centrifugal pumps are a low capital cost option often found in filter press feed applications . Operations range from high capacity and low pressure to low capacity and high pressure . Little of the operation is at the best efficiency point . Damage to the centrifugal pumps occurs from cavitation or recirculation on either end of the operating range . In some instances the centrifugal pump incurs substantial damage from abrasive wear in just a few weeks .
“ Piston diaphragm pump operation ranges from full capacity and low pressures to low capacity and high pressure by varying the stroke rate of the pump . Pump efficiency remains constant during this transition . This is accomplished using a pressure transmitter and variable frequency drive .
“ Piston diaphragm pumps , while greater capital cost , can pump to a filter press without experiencing undue abrasive wear and while maintaining efficiencies greater than 90 %.”
Reciprocating piston pumps produce a pulsating flow . Pulsations can cause vibrations in piping , excessive acceleration head , and influences on downstream processes . Pulsation can be dealt with adequately with pulsation dampeners .
“ One type of dampener is the bladder type . Air or nitrogen is added to the top of the vessel above the bladder at 70 % to 80 % of the process pressure . The pressure above the bladder does not need to be adjusted as long as the operating pressure is fairly constant .
“ With varying pressures , as with a filter press feed operation , the bladder style is inadequate due to the changing pressures . An air cap dampener is preferable . Air within the vessel is compressed by the slurry and the pulsations are attenuated . Air or nitrogen needs to be added regularly to the discharge dampener to replace that carried out by the slurry .
“ The amount of residual pulsation is a function of the stroke volume of the pump , the operating pressure , the volume of the dampener , and a constant for the pump . A 10 % residual pulsation is a good value for most applications .
“ When transferring solids such as thickened tailings , or paste , hydraulically actuated piston pumps are often employed . These machines have two reciprocating pistons . No diaphragm is used . Material is fed to the machines by an auger . Efficiencies are typically less than a hydraulic piston diaphragm pump but they are capable of handling thicker solids than can be fed into a hydraulic diaphragm pump .
“ Piston diaphragm pumps ( sometimes also called hydraulic membrane pumps ) operate typically at efficiencies near 90 %. Materials need to be fluid enough to flow into the pump . Some materials are thixotropic and can be sheared with an auger such that they will flow into a piston diaphragm pump .
“ The dividing line between piston and piston diaphragm selection is near 70 % solids for many mineral slurries . One rule of thumb suggests that if the slurry is less than 45 % solids by weight it may be amenable to flow into a piston diaphragm pumps . Laboratory testing is
One of two hydraulic membrane pumps installed for backfilling service at a mine in Peru
recommended to confirm which style of pump to select .”
Concluding , Kesler notes : “ centrifugal pumps are the most common pumps and generally have the lowest capital cost . However , when one considers efficiency , abrasive wear , pressure per stage , water usage , energy consumption , down time and other factors ; positive displacement pumps , and more specifically , piston-diaphragm pumps , are the better choice .”
In May , GIW Industries , leader in the design , manufacture , and application of heavy-duty , centrifugal slurry pumps , announced its 125th year in operation . The evolution began from a small foundry and machine shop in Augusta , Georgia in 1891 , under the name Georgia Iron Works . GIW began building slurry pumps in 1914 , closely examining clients ’ most demanding applications and finding solutions became a successful way of operating . This hands-on approach has taken employees around the globe to wherever companies demand systems that expand the limits of moving slurry .
Although the GIW ® Minerals High-Volume Froth ( HVF ) Pump has been on the market for six years , the company has announced new updates that make this innovative pump even more beneficial to mining . Its revolutionary design helps remove excess air from the slurry process . This is remarkably valuable , as traditional pumps often struggle with air bubbles that can cause pumps — and operations — to come to a grinding halt .
Air injected into slurries creates bubbles . “ The small particles ( of valuable mineral ) adhere to the bubbles , allowing them to be extracted ,” explains Richard Inglett , GIW Industries Product Manager . The problem in these applications , according to Inglett , is that a regular pump is meant to pump fluids , not air .
110 International Mining | SEPTEMBER 2016