Slurry Pumps

Apart from the usual guarding of rotating components, it is important to get advice from the manufacturer or their dealer. This is especially true if buying a Pump secondhand — just because the manual says it was designed to pump 2,000 gpm, it may not pump anywhere close to that if the duty isn’t the same as the original. Each duty is very specific. Let’s say you installed the Pump and had the wrong size pipe, you could have a critical issue with material settling out, which may even cause the Pump to explode.

This phenomenon has been reported by the Mine Safety and Health Administration (2009 bulletin) as a major concern. If a condition occurs that blocks the inlet pipe and outlet pipe of the Slurry Pump, it is estimated that 40% of the energy from the motor will go to heating the contents of the wet end of the Pump. The heat rise can be rapid and steam pressure will build, and an explosion can occur. Confirming the correct flow rate to keep materials in suspension and maintaining the design percent solids and particle size can reduce this risk. Installing power and pressure monitoring sensors that are interlocked and/or alarmed are also advised.  McLanahan’s recently developed thermocouple device is another safety feature when fitted and alarmed.

Good process design, proper mechanical design of sumps and piping, and use of safety related add-ons are factors determining the safe operation of a Pump. The manufacturer is always the best place to start.

Because the Pump is running at fixed speed and hasn’t been told that you removed a section of pipe, it will keep spinning away but now finds it is easier to pump. If you look at your pump curve, you will see that if you lower the head (resistance) that the Pump is pumping against, the new duty point will move to the right and the speed curve and head will intersect at a higher flowrate. The higher flowrate means more work is being done and thus power demand is greater. It would be the same if you reduced the height you are pumping to. The opposite occurs if you increase the head by adding pipe or vertical height to the discharge point. The danger with increasing the head without changing the speed is the lower flowrate that results, which may be below the critical setting velocity. Contact the manufacturer if you are contemplating changes to any part of your pump system.

McLanahan’s bearing assemblies are designed around the use of grease lubrication — this means that the seals being used are not suitable for oil. It is more complicated to design for oil and any leakage is far more troublesome for both lack of lubrication and the spillage. Grease lubrication simplifies maintenance and is appropriate for the rpms typically seen in this type of equipment

Rather than just say no, which would be the first reaction from any Pump manufacturer, let’s examine why you probably don’t want to consider this. From our perspective, 90% of problems are on the suction side of a Pump. Of those problems, 90% of those are associated with poor sump design, such as wrong wall angles (buildup in valley angles and corners), too shallow (vortexing), too big (settling and sloughing), too small (air entrainment, vortexing) and incorrect suction line (entrainment and NPSH issues). The science of sump design doesn’t start or finish with a cube or an old truck-mounted water tank — a correctly designed sump can save you many thousands of dollars in maintenance on your Pump, or even save a life.

How hot are they? McLanahan’s bearings are designed to run at a relatively high temperature — we set a maximum of 120^o C (248 ^o F). Possible reasons for bearings running hot logically include bearing failure; however, typically there will be other symptoms, such as unusual noise. Bearing failure can occur soon after gland failure if slurry has entered the seal at the wet end of the Pump.

It may simply be a faulty bearing. Were original equipment manufacturer bearings used during the last repair? It wouldn’t be the first time that price over value resulted in low-quality bearings being substituted.

Failure, or symptoms of failure, can also occur due to high belt tension (drive end) or air entrainment or cavitation (wet end), which will ultimately damage the bearings. Confirm the temperature rise (rises over time or almost immediate) and ultimate temperature. Look for other symptoms, such as noise. Ensuring personal safety, use a listening stick against the housing for signs that the bearings are not running smoothly. Consult the factory with the range of symptoms. 

Fortunately, McLanahan’s bearing assemblies are simple to repair — purchase a bearing repair kit and follow the instructions. Be prepared with an oven for heating, but the assembly requires no preload settings — just locate the bearings in place, lubricate and put the end caps on, finish lubrication and you are done.