What to Consider Before Buying a Centrifugal Slurry Pump

The majority of the centrifugal slurry pump issues do not begin in the field: they begin at the purchasing level. The incorrect choice of the material, the improperly sized impeller, or the inappropriate motor may make a good pump a pain in the neck. To ensure you choose a Centrifugal Slurry Pump with a long lifespan and high efficiency, here's a comprehensive pre-purchase considerations guide.

What Factors Should Be Considered Before Buying

1: Know Your Slurry Before Anything Else

You must know what you are pumping before you even examine a single spec of centrifugal slurry pump. This may seem like common sense, yet this is where most buyers make a slip and later on regret it.

Important facts to know about your slurry:

• Particle size: Do the solids have small particle size (as in clay or fine sand) or do they have large particle size (as in gravel or ore)?

• Particle shape: Rounded particles are less aggressive to pumps. Angular, sharp particles will result in quicker wear.

• Solids concentration: Percentage of solids in the mix? Increased concentrations translate into increased wear and increased power requirements.

• Slurry density: Slurries with high density require more power and tougher material.

• Chemical properties: Does the slurry contain acidic, alkaline or corrosive properties? This influences the choice of materials.

• Temperature: Hot slurries require special materials and seals.

These numbers can be obtained by your process engineer or by running a slurry analysis. Don't guess. These are the inputs that lead to all the ensuing decisions.

2: Match the Pump Size to Your Flow Requirements

This is the most technical section of purchasing a centrifugal slurry pump. But it is not difficult, when you know what you want.

You need to define two things:

• Flow rate (Q): What volume of slurry (in cubic meters per hour or gallon/minute) must flow?

• Total dynamic head (TDH): The sum of the pressure that the pump must be capable of overcoming, due to elevation, pipe friction and velocity head.

After you have Q and TDH, you may plot them on a pump curve. A right pump is a pump in which your operating point lies in the efficient region of the pump, which is usually the middle third of the pump curve.

When a pump is run on the edge of the curve, it wastes power and creates wear. Select a pump that runs at almost the optimum efficiency point (BEP).

According to the Hydraulic Institute, pumps that work near their efficiency point can last two to three times longer than pumps that do not.

3: Choose the Right Materials for Your Application

The materials you choose can make a difference in how long your pump will last. For example a pump made with the materials can work for two years while one made with the wrong materials may only work for six months.

The important materials to consider when using slurry pumps are:

• High-chrome alloy: It is very hard and suitable, for coarse highly abrasive slurries.

• Natural rubber: Performs well with fine, rounded particles at lower velocities. Absorbs impact but does not crack.

• Polyurethane: This is a good substitute for rubber in light to medium-duty applications.

• Stainless steel or duplex steel: It is applied in cases where corrosion is the primary hazard and not abrasion.

The liner and the impeller bear the brunt of the punishment and here is where you should concentrate your material choice. There are pumps that have interchangeable wet-end components, giving you a choice of metal and or rubber components based on the kind of pumping you are doing.

4: Evaluate the Impeller Design

There is only one critical component of your centrifugal slurry pump, the impeller. Get it wrong and all the rest is irrelevant.

In the majority of slurry applications:

• Close impellers are more efficient but may clog in the event of large particles.

• Open impellers can be used with larger particles and they can be unblocked easily.

• Recessed (vortex) impellers are used for very coarse or fibrous slurries that would clog a standard impeller.

The number of vanes should be taken into account as well. The smaller the number of vanes, the larger the passages: again, more suitable to large solids, but somewhat less economical. Increased numbers of vanes enhance efficiency, although they may become clogged with rough material.

5: Check the Drive System and Motor

The motor and the drive system need to match the pump. People often make a mistake when they get a motor that's too small especially when the density of the slurry or the flow of the slurry changes.

Key things to think about when it comes to the motor are:

• Power (kW or HP): You need to get a motor with a service factor. For slurry pumps most engineers think you should get a motor with 10-20% power than you need.

• Speed (RPM): If you get a motor with a speed it will last longer but you might need a bigger pump. You need to find a balance between the speed and how long the pump will last.

• Drive type: A direct drive is simple. Works well. A belt drive lets you change the speed. A variable frequency drive gives you the control over the pump.

Variable frequency drives are an investment for most people who use slurry pumps. They let you slow down the pump when you do not need much flow, which saves energy and makes the pump last longer.

6: Look at Seal Options Carefully

The seal system is what keeps the slurry inside the pump. If the seal is bad you will have leaks. The pump will not last long.

There are three types of seals for centrifugal slurry pumps:

• Packing gland: This is a traditional type of seal and it is not expensive. It needs water to flush it and you need to adjust it sometimes. It is not good for slurries that're very abrasive or hazardous.

• Mechanical seal: This type of seal is more reliable. Needs less maintenance. It needs clean water to flush it.

• Expeller seal: This type of seal does not need water to flush it. It uses an impeller to keep the slurry away from the seal. It is good for places where you do not have a lot of water.

7: Think About Maintenance and Spare Parts

Slurry pumps will wear down over time. It is not a question of if they will wear down. When. So before you buy a pump you should ask some questions:

• How easy is it to replace the impeller and the liners?

• Can you get parts near you or do you need to import them?

• How long does it take to get replacement parts?

• Does the company that made the pump offer support?

A pump that is cheap to buy but expensive to maintain is not a deal. You should think about how much the pump will cost you in the run, not just how much it costs to buy.

Some companies that make pumps offer parts that can be used on types of pumps, which makes it easier to keep track of your inventory.

CNSME Pump offers a range of centrifugal slurry pumps that can be customized for mining, dredging and process industries. You can look at their products here. 

Final Thoughts

Buying a slurry pump is a big decision. You should take your time. Make sure you understand what you need. You should size the pump properly choose the materials and pick a company that will support you. The pumps that last the longest are the ones that were chosen carefully. Not the ones that were the cheapest. You should do your research. Think about the long term.

CNSME Pump, a professional slurry pump manufacturer, can customize centrifugal slurry pumps to meet your specific needs. Please contact us for more details!