Why McLanahan Slurry Pumps
McLanahan Slurry Pumps feature a split casing design to allow easy access to the liners, the impeller and the gland for maintenance. Most Slurry Pumps come with an assembly aid arm to support the suction casing during impeller replacement and gland maintenance. This feature allows the technician to swing the casing away from the Pump instead of dropping the component to the ground or using a crane.
McLanahan Slurry Pumps feature field replaceable wet-end liners to facilitate an ease of maintenance. These liners are self-gasketing to provide a reliable seal. Several compounds of rubber are available for various duties: a natural rubber blend for high abrasion resistance and nitrile for different chemistries.
Three styles of gland are available with McLanahan Slurry Pumps:
- D-Type glands are our most fitted gland and feature a rotating rubber seal ring and a static ceramic face. These two highly abrasion resistant components are adjusted such that a minimal amount of slurry is allowed to pass through between the surfaces to act as lubrication. This gland design absorbs little energy and requires no external lubrication; although in some cases it can be fitted with flushing water. This design is ideal for applications where clean process water is unavailable or dilution of the slurry being pumped is undesirable. This design is not recommended for more viscous types of slurry.
- H-Type glands have the lowest maintenance needs but require a reliable consistent fresh water supply of 1-5gpm at 3-5psi above pump discharge pressure (0.2-1 m3/hr at 20-25 kPa above). This gland features two rubber seals separated by a lantern ring where the pressurized water is injected. The outer seal is adjusted to allow gland water to seep out for lubrication, while the water at the internal seal flushes solids away from the seal. This gland is ideal for applications such as Thickener underflow.
- P-Type glands are the classic design and are the most common in the industry. Specialized packing rings are wrapped around the gland sleeve and compressed to make a seal. This gland requires an external water source to lubricate the packing and will leak small amounts of process water to atmosphere. Clean water is most critical to this gland, although in some cases a grease lubricated gland can be supplied with hydrocarbon-compatible liners and components.
Each of these glands is designed to seal the pressurized wet end of the Pump from the atmosphere. All glands have a gland sleeve to protect the shaft from abrasion. Seals and components are manufactured from abrasion/corrosion resistant materials.
McLanahan also offers two designs of impellers: closed vane and open vane. Closed vane impellers are molded from high quality rubber over a steel skeleton. It is designed to maintain efficiency over a much longer period than an open vane and requires no added maintenance to adjust the clearance at the suction liner interface. Typical open impellers allow significant bypass as they wear, and efficiency reduces dramatically.
Open vane impellers are not a recessed impeller style Pump. They are the standard Pump head with a vortex flow design impeller that impels fluids through and out of the casing. Open vane is the choice for solid and fibrous material with a minimal risk of clogging, such as in agricultural applications separating manure from bedding sand.
McLanahan's bearing assembly is exceptionally simple but nonetheless long-lasting. Unlike other manufacturers, the bearing housing reassembly process requires no preload setup given the wet-end, heavy-duty roller bearing and the drive-end, double-row, self-aligning, spherical roller bearing. Fit the components into the housing per the Installation, Operation and Maintenance Manual, lubricate as instructed and you are ready to go. Factory rebuilt bearing assemblies are available for the most urgent of maintenance.
How Slurry Pumps Work
Using the conversion of rotational kinetic energy into the hydrodynamic energy of the fluid flow, centrifugal Slurry Pumps motivate fluid flow along pipelines. Pump rotation, and thus rotational energy, is typically created by the electric motor driving the Pump shaft through a V-belt drive. The fluid enters axially into the eye of the Pump impeller, which by its rotation acts tangentially and radially on the fluid. The fluid is accelerated by the impeller gaining velocity and pressure, flowing radially outward into the casing, decelerating but building pressure. Being pressurized, it then exits the volute. The displaced fluid in the Pump head is replaced by atmospheric pressure and static pressure acting on the fluid in the sump, pushing it into the impeller.
The speed of the Pump is regulated by the ratio of the transmission plus, in some cases, the use of a variable frequency drive to tune the speed for a more exact duty. Care needs to be taken not to use high turn-down ratios, which result in the loss of power. Head or more specifically total dynamic head, which is the sum of static, friction and pressure heads, is used to find the speed head. Calculated water head is corrected (HR) using the d50 of the particles being pumped, the percent solids by volume. Horsepower is calculated as work done and thus includes the fluid specific gravity. Reference should always be made to the manufacturer’s curves to ensure the Pump is operating in the most efficient zone.
It should be noted that this design of Pump, unlike a self-priming positive displacement Pump, does not actually suck the fluid into the casing. As discussed above, the fluid flows into the Pump based on atmospheric pressure and the height of fluid in the vessel (14.5 psi or 33.5ft.hd. [10mhd] + the height to water level in the Sump).
Other factors affect the performance of the Pump, most important of which is the Net Positive Suction Head (NPSH), which is not only an equipment issue but a system issue. NPSHA is a measure of how close to vapor pressure the fluid becomes. NPSHR is head value on the suction side that is required to keep the fluid from cavitating. Heated solutions are particularly prone. Significant damage can occur to the impeller and bearings when a Pump is cavitating.
The reverse function of the centrifugal Pump is as a water turbine converting potential energy of water pressure into mechanical rotational energy. Examples of this are in tailings disposal down long inclines to ponds. Special builds are required.
Lining materials vary and are typically selected based on the materials to be handled and any chemistry present. Most sand sized materials <5mm (4mesh) can be handled effectively by the use of the high-quality natural rubber compound liners. Gravel should be handled by hard metal Pumps, such as Ni-Hard or Hi-Chrome (27%).
Popular Applications for Slurry Pumps
Slurry Pumps are ideal for construction sand, sports sand, specialty sand, tailings, cement, metalliferous mining, pulp and paper, water treatment, stone flour, Thickener underflow and environmental applications.
Benefits of McLanahan Slurry Pumps
- Field replaceable wet-end liners for ease of maintenance
- Self-gasketing liners to provide a reliable seal
- Several compounds of rubber are available for various duties
- Natural rubber blend for high abrasion resistance is available in different durometers typically between 40A and 60A
- Nitrile and neoprene are also available for different chemistries
- Three styles of gland: D-Type, H-Type and P-Type
- Glands are designed to seal the pressurized wet end of the Pump from the atmosphere
- OSHA compliant steel guards covering all moving parts.
- Vertical configurations can be manufactured upon special order
- A drain plug on the suction-side casing to drain the wet end of its contents
- Two impeller designs available: closed vane and open vane
Frequently Asked Questions
What can you recommend to increase safe operation of my Pump?
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.
When I reduced the length of pipe line, why did the Pump trip out on overload?
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.
Can I use oil in my bearings?
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
I have an old Pump sump that my grandfather used in our old plant, can I use that for my new plant?
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.
My bearings are running hot, what should I do?
How hot are they? McLanahan’s bearings are designed to run at a relatively high temperature — we set a maximum of 120o 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.