The main difference between slurry and wastewater pumps is in the parts that are in direct contact with the slurry and thus subject to wear by the slurry's solid particles.
Read more
The three parts to pay close attention to are:
- Motors
- Shaft and Bearings
- Seals
Motors
Important factors for slurry pump motors:
• Effective cooling
• Insulation
Effective cooling
Water cooling is superior to air cooling and gives the submerged motor a high power density and comparatively low temperature.
In the Flygt motor, developed and manufactured by Flygt, the rotor diameter is bigger and the stator thinner than in standard motors. This directs more of the losses (heat release) to the stator and to the surrounding, cooling liquid. The short heat transfer distance makes the cooling effective and keeps the working temperature low.
The pump can be cooled in three ways depending on the slurry temperature and other circumstances:
• Pumps that work fully submerged in slurry, can be cooled by the ambient liquid. The slurry temperature may not exceed 40°C.
• Pumps that work at times with the motor partially or totally un-submerged, can be equipped with a cooling jacket for internal cooling, where a cooling medium (glycol mixture) circulates (/ series).
• Pumps that often work in a low level, in hot slurry or are dry installed can be cooled using an external supply of cooling liquid, connected to the cooling jacket. This is also how to cool a partially or totally un-submerged slurry pump from the series since these pumps don't have the internal cooling option.
Cooling of the series with the big Great and Gray drive units requires a more detailed explanation. Please see the Installation Manual for details.
Insulation
Class H insulation (180°C) is applied to the stator winding by a trickle impregnation system. The Flygt pump has a motor limit to Class B (140°C), which reduces thermal stress resulting in an extended lifespan.
Trickle impregnation gives a winding fill much greater than typical dip and bake systems. This gives much higher protection against short circuits in the winding.
Shaft and bearings
Important factors for shafts and bearings:
• Shaft design and dimensioning
• Bearing type and protection
Shaft design and dimensioning
The shaft and bearings are of sturdy design. The distance between the lower bearing and the impeller is minimal, eliminating shaft deflections. This provides long seal and bearing life, low vibration and silent operation.
Bearing type and protection
All slurry pumps have two row angular contact ball bearings as the main bearing, because they give a high load capability in the radial as well as the axial direction.
The bearings are well protected with a lifetime lubrication of high performance grease.
Seals
Important factors for submersible pump seals:
Goto INDUX to know more.
• Low leakage or even zero leakage!
• Wear resistance
Leakage and wear resistance
In conjunction with leakage rate, the most important feature for seals in slurry applications is the ability to resist wear from abrasive particles.
The seals for the slurry pumps are designed to cope with highly abrasive pump media. Only the seal rings are exposed to the media. Other parts of the seal, such as springs and torque locks are protected from wear, clogging and corrosion inside the seal housing.
In addition, an isolation zone takes the pressure off the mechanical seal.
The pre-mounted Plug-in™ seal unit (/ series) is fast and easy to handle. The seal faces are closed and cannot be contaminated or damaged during service. The seal rings made of Tungsten carbide are always properly aligned to eliminate run-out.
Active Seal™ offers increased sealing reliability and zero leakage into the motor, thus a reduced risk for bearing and stator failure.
Active Seal™ features a rotating inner seal ring with laser cut pumping grooves that acts like a micro-pump, continuously preventing liquid from entering the motor.
It all adds up to:
• Reduced downtime
• Fewer required service inspections
• Fewer unscheduled maintenance checks
• Lowering your operation costs
Protection systems
Important factors for submersible pump protection:
• The possibility of detecting a leaking seal before any damage occurs
• Spin-out™ seal protection
• Overheating protection
Possibility of detecting a leaking seal
series: In the area that contains cooling oil above the seal, there is a sensor that emits a warning if water enters. In addition, the oil is discolored by water leakage and this can be seen through an inspection screw on the side of the pump.
Stator housing leakage: A float switch shuts the pump down if water is detected.
/ series: The inspection chamber between the seal unit and the bearings has a built-in sensor for early detection of fluid leakage. The space can be inspected and emptied via a screw, which is easily accessible from the outside.
Spin-out™ seal protection
Flygt pumps use a patented outer seal design that protects the seal by expelling abrasive particles.
Overheat protection
Thermal sensors are embedded in the stator windings to prevent overheating.
If you want to learn more, please visit our website Slurry Pump Manufacturers.
We are having some problems with an installation we just put in operation a month ago.
We are having some flow restrictions and we don’t know the cause.
We are pumping lime slurry (density gpl, temp about 60ºC).
The installation consists on a feeding tank, a centrifugal pump, a pipe ring, and 5 feed points with a control valve each one.
The tank is about 10 m3 capacity with an agitator.
The pump is centrifugal, with variable speed drive, rpm max, and 90 m maximum head. The vsd is controlled by the flow returning to the tank
The pipe ring is about 800 m – 4” to the feeding points, and 3” on the returning to the same feeding tank. We are pumping about 60 m3/h on the 4” line, and returning about 40 m3/h on 3”.
The feeding points have their own control valves and flow meter each one.
We have a pigging system to clean the line. The bends on the line are 10D radius, and the valves are ball valves full pass.
In normal operation the pump is working around 8barG on the impulsion, about rpm. But sometimes, the speed and the pressure starts to increase slowly, (let says, in 5 hours), and we it reaches the maximum speed (rpm, 10 barg) the flow returning to the tank starts to drop, and in a matter of 2-3 hours falls to nearly 0.
We haves some manometers on the feeding points, and with that and the % open of the valves, and the flow meters, we can see that there is no blockage on the 4” inches line.
So we are guessing that there is a blockage on the 3” line.
The thing that annoys me is that we have achieved a partial solution that consists on connecting a ½” hose to the pump suction and feed it with water.
As soon as we connect the hose, the flow stars to increase again, and in a matter of 20 minutes it reaches its normal condition and works properly.
His tends to happen by 2-3 times per week.
If is a matter of blockage on the 3” line, and the water helps to clean the line, why as soon we connect the hose the pump starts to increase the flow? The water would need about 20 minutes to run the 4” line and another 15” to return to the tank, so I suppose the should expected to have to wait about 30 minutes or more to see any improvement on the flow.
I am really lost with this, and any help would be appreciated.
It does sound like you are slowly plugging a line. The 4” line looks to be more likely the problem looking at the velocity. After the fourth or fifth feed point (depending on where you go to 3”) the velocity must be getting quite low in the 4” line. Slugs of slurry may be migrating to a point that they can slowly choke back the flow. As far as the garden hose getting things going it makes sense, for practical purposes liquids are not compressible and your system is a loop, liquid in will mean liquid out. You are diluting and possibly cooling the slurry also. There are many variables but velocity is very suspect with the symptoms you describe. Another possibility is that the liquid is a dilatant or pseudo-plastic and you are whipping up a creamy slurry or maybe just air trapped at the impeller eye.
Regards checman
If the pump has a enclosed impeller, it is possible to have a air lock in the impeller. I assume the lime slurry have a high tension between the air-liquid surface. The flush water can dilute the lime and reduced the surface tension, so the liquid brought the air away gradually.
If there is a high point in discharge piping close to the pump, there may be a air pocket there. with reduced surface tension, it can be gradually brought away by the liquid. However, this possibility is low except there is something special in the pipe.
It does not look like any blockage at the suction pipe since you never noticed any cavitation. At 60C temp and major blockage at suction line, I would expect serious cavitation. But it is possible that air accumulated at the reducer and then entered the impeller eye and locked the impeller.
Dimtec,
You’re right, I wanted to say 4". Because I thought after the first feeding point Q will be reduced and you don't have 60 m³/h any more. That is getting worse close to the last feeding point.
option one- as I mentioned the problem is in the suction line ( more possible). By having Flexible Transparency Hose ( 4" ) as a suction line ( without any branch, bend, low point and so on. the problem will be solved. I saw the same problem many time in suction lines.
option two -Some companies use a flushing water connection with a solenoid valve. The valve gets open timely and flushes the line periodically.
Option three- if you have ant pressure/flow control on the recycle line such as back pressure control valve or flow orifice (FO is not a right application for this service)adjust them for lower presure and increase pump flow rate. by this you can increase the slurry velocity in the loop.
there is no scale issue. it's solid build up issue and may happen at low points, bends, branch connections, vertical points ....
Hope it does work.
Kavous
To check the discharge pressure is necessory and may give you answer to your questions.
There is unlikely solid settling in the suction pipe. 7fps velocity is pretty high for a 4" suction pipe. Even if some settling in the pipe, It's pretty easy to be brought away when the local velocity increased. I would prefer the reducer at the suction line top-flat instead of bottom flat because the bottom flat will make air bubbles accumulated at the top of the reducer.
To find out if there is air lock in the impeller or not, you can check the pressure gauge at the discharge pipe when the pump start to speed up. When the pump speed-up, the discharge pressure shall keep the same and when the pump reached max. speed, the discharge pressure starts to drop, so the recirculated lime reduced.