Understanding Pump Curves

Understanding Centrifugal Pump Curves  

Once a pump is properly selected and installed in a system, operation should be trouble free. However, in existing systems, or as pump and system conditions change, problems may develop. Following are some troubleshooting hints to help identify and solve problems.

When selecting a centrifugal pump, one should match the performance of the pump to that needed by the system. To do
that, an engineer would refer to a pumps composite curve. A typical composite curve includes the pump performance
curves, horsepower curves and NPSH required. A pump performance curve indicates how a pump will perform in regards to pressure head and flow. A curve is defined for a specific operating speed (rpm) and a specific inlet/outlet diameter. In our example below, these curves show the performance at 1450 rpm for a 3” inlet/2” outlet. Several curves on one chart indicate the performance for various impeller diameters. In the example below, the impeller size ranges from 6.3” to 8.7”. These curves also tell you the possible conditions that the pump could be modified to meet
in the future by installing a different impeller size. Flow is indicated on the x-axis while pressure/head is indicated on the y-axis. In this example, if pumping
against a head of 40 ft using an impeller size of 7.9”, you could pump at a rate of 140 gallons per minute. Typical centrifugal pumps will show an increased flow rate as head pressure decreases. The curve also shows the shut off head or the head that the
pump would generate if operating against a closed valve. In our same example, the shutoff for the 7.9” impeller is 45 ft of head. The pump performance curve also provides efficiency curves. These efficiency curves intersect with the head-flow curves and are labeled with percentages. The efficiency varies throughout the operating range. In our same example with the 7.9” impeller, we can see that at 140 gallons per minute, the pump is operating at 72% efficiency.

Some curves will also mark the Best Efficiency Point (B.E.P.). This is the point on a pump’s performance curve that corresponds to the highest efficiency and is usually between 80-85% of the shutoff head. At this point, the impeller is subjected to minimum radial force promoting a smooth operation with low vibration and noise. Pumps run best at or
near BEP. Operating the pump outside of the recommended range will most likely shorten the pump life. BHP (brake horsepower) curves indicate the horsepower required to operate a pump at a given point on the performance curve. The lines on the horsepower curve correspond to the performance curves above them and, like the head-flow curve, the different lines correspond to different impeller sizes. This information is useful to ensure that the selected motor is the correct size and is also used when calculating power consumption costs. If we take our same example of a flow of 140 gpm using the 7.9” impeller, the power demand is 2 hp.

When sizing a motor, the total current and future demand should be considered to make sure that the motor is the correct size. The motor is typically sized not at the peak efficiency point but by the maximum power draw that will be needed. It is common practice to size the motor for the End of Curve (EOC) horsepower requirements. In the example shown, even though 2 hp is required for a flow of 140 gpm with 40 ft head, the end of curve horsepower requires a 2.5 hp motor be used.

NPSHr Curve
The 3rd part of the pump curve is the Net Positive Suction Head Required (NPSHr) curve. The NPSHr curve provides information about the suction characteristics of the pump at different flows. The x-axis is still measured in flow units (gallons per minute), but the y-axis is now measured in feet of NPSHr. Each point along the curve identifies the NPSHr required by the pump at a certain flow to avoid cavitation issues that would be damaging to the pump and would have a negative impact on overall pump performance. In other words, the NPSH available must be greater than the NPSHr to avoid cavitation. Looking back at our example design flow of 140 gallons per minute, we can see that this pump will require approximately 2.5 ft of NPSHr at that condition. Generally speaking NPSHr does not vary dramatically between variations in impeller trim which is why we do not see separate curves for the minimum and maximum impeller trims. Those curves are actually present, but they are overlaid by the designtrim NPSHr curve.

Composite or Quick Selection Curve

Often, an entire line of pumps of one design can be shown in a composite curve to give a complete picture of the available head and flow. These charts provide flow, head and pump size only. For more specifics, you must then refer to the specific performance curve for impeller diameters, efficiency and other details.

If you want more information, contact us by phone or email. 

Trouble shooting a pumping system

Trouble Shooting a Pumping System 

Once a pump is properly selected and installed in a system, operation should be trouble free. However, in existing systems, or as pump and system conditions change, problems may develop. Following are some troubleshooting hints to help identify and solve problems.

If you want more information, contact us by phone or email. 

Trouble shooting a diaphragm pump

5 Minute Fix to Troubleshoot a Diaphragm Pump

Air-operated double diaphragm pumps (AODD) are preferred in transfer applications due to a simple design that makes
them easy to operate and cost effective to repair. But it is important to install and operate the pump correctly to achieve
top performance. Highlighted below are six quick and easy fixes to common problems you may encounter during
installation and operation.

Step 1. Check the Inlet Air Line Size and Pressure 

Installing too small of an air line is the most common mistake relating to an AODD pump. By using too small of an air
line, you are starving the pump of the fuel – compressed air – it needs to operate at peak performance. Double
diaphragm pumps come in all shapes and sizes, based on the application and fluid requirements. Larger AODD pumps,
one inch and greater, require more compressed air and larger air lines to operate at full capacity compared to smaller
pumps. You can find the appropriate air line size for your pump in the manufacturer’s installation and operation
manuals. As a general guideline for AODD inlet air line sizes, it is best practice to match the air line hose size to the air inlet port size on the air valve.

Inlet air pressure also plays a key role in getting the
most out of your pump. Diaphragm pumps operate
on a 1:1 ratio, meaning the pressure of the inlet air
you feed the pump is directly related to the fluid
pressure at the outlet of the pump. For example, if
the target outlet pressure of a 1 inch, 50 gpm pump
is 100 psi, the inlet air pressure entering the air
valve of the pump must be greater than or equal to 100 psi.

System back pressure and fluid viscosity will impact
the outlet fluid pressure. Too little back pressure may cause the pump to run inefficiently because the ball checks may not check as quickly. Too much back pressure can cause the pump to stall if the fluid pressure overcomes the air pressure to the pump. To control the performance (flow and pressure) of an AODD, it is important to have an air regulator assembly installed to control the incoming air pressure (see Figure 1, C). Installing the correct air line size with an air regulator will solve the most common installation problem found with AODD pumps.

Step 2. Inspect for Muffler Icing and Restrictions

Diaphragm pumps can generate high decibel levels at full speed, which is why mufflers are included and recommended
at install. The AODD air motor requires compressed air to operate. As the compressed air enters the air valve and is channeled through the pump center section to exhaust through the muffler, rapid changes in temperature occur. At the muffler exhaust, air temperature is well below freezing and can cause icing-related issues, increasingly common in humid environments. If your pump is operating erratically, or if the inlet air has high levels of moisture or you see frost on the outside of your muffler, these are all indications you are having an issue relating to icing that is decreasing your pump efficiency. Suggested below are solutions you may implement to eliminate these issues and restore your pump performance.

 Decrease the air pressure to the pump
 Increase size of pump to operate at lower speed (i.e., lower air pressure)
 Exhaust the air to a remote location via an exhaust port tube
 Add an air line filter with a water catcher and drain to collect condensation
 Install an air line heater, raising the exhaust air temperature above freezing
 Adjust pressure dew point temperature with an air compressor dryer 

Step 3. Inspect Sealing Surfaces for Leaking 

Leaking is a very common problem in all types of pumps. But there are some simple fixes to ensure the fluid stays in your AODD pump and not on the ground. First, it is important to know that pumps, especially plastic pumps, need to be
torqued to the manufacturer’s recommended rating. Reason being, materials relax over time, often referred to as cold flowing, which can cause sealing surfaces to loosen and create leak paths. Always refer to the pump manual for torque values and follow the bolting patterns illustrated to reduce the threat of leakage. A wise maintenance technician once said, “There are two types of pumps – those that leak and those that are going to leak.” Reuse of PTFE O-rings is another cause of leaking at sealing surfaces. PTFE is a versatile material, but one of its downfalls is resilience. Once a PTFE O-ring has been compressed, it is not capable of regenerating its original shape. So replace all pump PTFE O-rings when servicing an AODD pump. After properly torqueing your pump per manufacturer recommendations and ensuring all sealing O-rings have been replaced after service, your AODD should be leak-free.

Step 4. Ensure Proper Tubing and Piping Size 

Pump inlet and outlet fluid port diameters vary based on the flow rate required. It is critical that inlet and outlet hose sizes match the size of the pump. Of primary concern is the risk of cavitation and the negative effect it has on the pump, causing more frequent repairs and higher maintenance costs. For example, if a 1 inch pump has a ½ inch inlet hose connected, the pump will not be able to operate at full capacity without the risk of cavitation. This risk increases dramatically as the desired fluid viscosity rises. In this example, the 1 inch pump should have a 1 inch inlet and outlet hose attached to avoid cavitation and more frequent, costly repairs. It is also recommended that an AODD pump be installed with a flexible inlet/outlet connection rather than being hard plumbed. As pump speed increases, vibration increases. As vibration increases, the risk of loosening a hard plumb connection increases, creating the potential for leaking.

Step 5. Slow the Pump Down to Prime 

AODD pumps are popular when self-priming is required. Creating a low pressure zone, less than the atmospheric pressure of 14.7 psi, inside the fluid bowls is how the AODD pump draws fluid. If the air pressure supplied to the pump is too high, this will cause the pump to changeover too quickly and not allow enough time for the fluid to be drawn into the pump. To solve this priming issue, use the air regulator to decrease the air pressure entering the air valve and slow down the pump. Once the pump speed has been reduced and the fluid has been provided enough time to enter the pump, you can increase the air pressure and operate the pump at a faster speed.

Step 6. Clear any Fluid Line Restrictions 

The last step to ensure optimal pump performance is to clear any fluid line restrictions. These restrictions create back pressure that may negatively affect the pump and potentially create cavitation that will increase frequency of maintenance. Things to look for at both the inlet and outlet of the pump:
 Closed or partially closed valves
 Clogs or kinks in the line
 Too much hose or length of distance

Conclusion 

These quick fixes will solve most of the common problems you may encounter with an AODD pump. Remember to listen to the pump. Many times, carefully listening to the pump operate will tell you what you need to do to reach optimum pump performance levels. Listen for erratic operation, which may be caused by an inlet hose that is too small or a problem relating to icing. If you hear what sounds like gravel running through the pump or you see flashing around the manifold elbows, you are cavitating and need to correct the inlet or outlet tubing size or reduce the pump speed to minimize unnecessary maintenance. Keep an eye out for kinks in your inlet and outlet lines or any valves that could be closed or restricted. With these tips, you will achieve top performance out of your AODD pump and spend less time trying to figure out problems and more time pumping.

If you want more information, contact us by phone or email. 

Pumping Pet Food – Case Study

How we make it work better

A pet food manufacturer that we work with typically processes a number of meat slurries made of white fish, lamb, chicken, duck, turkey, etc. Due to the different meats and the fact that these slurries are kept in tank hoppers at 40 degrees F or colder, the viscosity of each slurry created pumping issues. The customer had used PD pumps with some success, but they were having to replace or repair these pumps frequently. They wanted a different solution that would minimize maintenance and allow them to pull the meat slurry out of the hoppers. The customer had used PD pumps with some success, but they were having to replace or repair these pumps frequently. They wanted a different solution that would minimize maintenance and allow them to pull the meat slurry out of the hoppers.

The M.G. Newell account manager thought that a twinscrew pump would be a good solution. He contacted the pump manufacturer who brought in a demo pump to try on the meat slurry. The twin screw pump was able to push the slurry through the 4” line and it was able to suck the slurry from the hopper. After the trial, the customer upsized to a 5” inlet on the pump to further improve the suction capabilities on this high-viscous slurry. The pump was sized to reflect a flow rate of 18 gpm with a 10HP gear reducer. This size will pump a meat slurry up to 23,000 cps. The customer is currently evaluating the pump on one of their 4 hoppers. If the pump continues to perform, they’ll be putting a twin-screw pump on the other 3 hoppers as well. Want to learn more about how twin-screw pumps work? Are they the right solution for your process? Click: Twin-Screw Pumps

 

If you want more information, contact us by phone or email. 

Pump Selection and Specifications

Pump Selection Criteria 

For sanitary processing, quick and efficient cleanability is critical when choosing a pump. To ensure a hygienically and microbiologically perfect condition of the final product, high standards are applied to centrifugal and PD pumps with regard
to hygiene and cleaning requirements. The surface finish influences the cleanability of pump parts. Cleaning times will decrease with improved surface finishes. Pumps for food, beverage or pharmaceutical industries are constructed of 316L stainless steel or alloys which provide a homogenous, pore-free surface. The product chamber should have no gaps or dead ends. Seal rings must be clamped in a way that they can be cleaned by the CIP solution. Non-metallic seals are typically made of NBR, EPDM, PTFE or FPM.1

The main purposes for creating sanitary design in pumps are to:
· make sanitation programs faster;
· make sanitation programs more efficient;
· make sanitation programs more economical;
· help prevent product adulteration;
· help satisfy regulatory requirements;
· help satisfy consumer/customer audits, demands and requirements.


Additionally, accrediting organizations, such as 3A, EHEDG, and the FDA, publish guidelines meant to specify the
technical requirements of pumps and other processing equipment. Full guidelines can be found on these organizations
websites.

Pump Specifications and Selection 

Pumps are commonly rated by horsepower, capacity or flow rate (US gallons per minute), outlet pressure (defined as meters or feet of head), and inlet suction (defined as suction meters or feet of head). The head can be simplified as the number of feet or meters the pump can raise or lower a column of water at atmospheric pressure.

Total Suction Head

where:
hs = static suction head
> 0 for flooded section
< 0 for flooded section
hfs = pressure drop in suction line
ps > 0 for pressure
ps < 0 for vacuum
ps = 0 for open tank

NBR – nitrile rubber; copolymer of butadiene and acrylonitrile; EPDM – Ethylene propylene diene rubber; a terpolymer of ethylene,
propylene and a diene-component; FPM – fluorinated propylene monomer; commonly sold under the trade name Viton®; PTFE –
polytetrafluoroethylene elastomer; commonly sold under the trade name Teflon®

Total Discharge Head

where:
ht = static discharge head
hft = pressure drop in discharge line
pt > 0 for pressure
pt < 0 for vacuum
pt = 0 for open tank

Total Head

where:
Ht = total discharge head
Hs = total suction head

From an initial design point of view, engineers often use a quantity termed the specific speed to identify the most suitable pump type for a particular combination of flow rate and head. Therefore, to ensure you choose the right pump for the application, the following is a list of questions you will need to answer.


Material Properties
What is the material being pumped?
What is the material viscosity?
What is the material density or specific gravity?
What is the particle size?
What is the temperature of the material?
Is the material abrasive?


Process Conditions
What is the desired flow rate?
Where is the feed tank relative to the pump?
What is the suction lift distance?
What is the head pressure?
What is the discharge distance?
What is the inlet and outlet hose diameter?


Other Considerations
What certifications are required (FDA, 3-A, EHEDG)?
Will it be used for COP or CIP?
What is the desired price range?
What is the pressure of the shop air?
Who will clean and service the pump?
What special applications need to be considered?


With these questions and answers in hand, you can discuss the best pump choice with one of our engineers.

If you want more information, contact us by phone or email. 

Pump Repair Training – Case Study

Pump Repair Training – Case Study 

A customer was having a difficult time with positive displacement pumps needing frequent and costly repairs. After discussions with the plant engineer and sanitation, we felt we had a good grasp on the cause of the problem.

That is where Pump Repair Training comes in. 

The plant had experienced a change in personnel over the last 3 – 6 months on both the sanitation and maintenance staff. Some of the basic steps in disassembly and reassembly had not been properly performed along with missing preventive maintenance steps. The pumps were able to perform, but damage was occurring causing inefficiencies and expense in the upkeep.

Preventative Maintenance

We review our findings with the plant engineer. We don’t suggest a new pump. Instead, we determine that a “refresher” training course is needed to make sure everyone knew the proper sequence of assembly and proper preventive maintenance requirements of positive displacement pumps.

The hands-on pump repair training, proves to be the key in getting the process to turn around and reduce the occurrence of breakdown. This has led to lower maintenance cost and more production operating time. We sometimes lose sight of the “basic” practices that keep our operations functioning smoothly. It is very important that routine training programs and PM plans are in place to review equipment procedures that keep your process running smooth, safe, and cost effective.

M.G. Newell and our equipment manufacturers offer plant audits that help assist you in maintaining your equipment and provide training and preventative maintenance programs. We realize in this “challenged” economy that everyone is looking for ways to tighten their process parameters and keep costs down. This is just another way that M.G. Newell makes it work better.

If you want more information, contact us by phone or email. 

Pump Rebuild vs Pump Remanufacture

Pump Rebuild vs Pump Remanufacture

Pump Rebuild and Pump Remanufacture is offered at SPX Flow, in conjunction with M.G. Newell, on standard WCB positive
displacement pumps. These options allow you to get a longer life from your pump and reduce the cost of product
ownership.

Pump Rebuild

Pump rebuilds are performed by M.G. Newell in any of our 3 locations – Greensboro, Louisville or Nashville. As a SPX Certified Repair Center, M.G. Newell has qualified factory service technicians on staff with over 30 years of experience. We invest in equipment, inventory and training to become one of a select group of distributors that are approved. In a rebuild, we pull the shafts, replace the bearings and all wear items. Depending on the amount of wear, we also replace the rotors. Our shop will perform an evaluation of the pump and provide you with an estimate to rebuild your pump. The cost of a rebuild is approximately 50% of the cost of a new pump. The only drawback to a pump rebuild is a slight loss in its original efficiency.

Pump Remanufacture

Pump remanufacture is performed by SPX Flow at their factory. In this program, they only reuse four parts: the SS cover, body, gear case and gear cover. The remaining components are completely replaced with new, original equipment parts manufactured to factory specifications. They bore the existing body and make new oversized rotors. This machining is the main difference between a rebuild and remanufacture. When complete, the pump is back to its original performance specifications and has a new 1-year warranty from SPX Flow. Due to the new oversized body, standard rotors should not be used due to potential damage or failure of the pump. A pump can be remanufactured two times in its lifetime. The cost of a remanufactured pump is approximately 75% of the cost of a new pump.

If you want more information, contact us by phone or email. 

Pump Problem Solving

Pump Problem Solving – Cavitation 

For all pump application problems, cavitation is the most common issue we encounter. It occurs with all types of pumps – centrifugal, rotary or reciprocating. Cavitation is the formation of vapor cavities in a liquid – i.e. small liquid-free zones (“bubbles” or “voids”) – that are the consequence of forces acting upon the liquid. It usually occurs when a liquid is subjected to rapid changes of pressure that cause the formation of bubbles where the pressure is relatively low. These bubbles are carried along by the fluid and implode instantly when they get into areas of higher pressure.

According to the Bernoulli Equation, this may happen when the fluid accelerates in a control valve or around a pump impeller. Cavitation can result in a loss of pump efficiency/flow, noise and possible damage to the pump and/or system. The vaporization itself does not cause the damage – the damage happens when the vapor almost immediately collapses when the velocity is decreased and pressure increased. When a pump cavitates, the vapor bubbles move toward the impeller where they collapse. 

This causes a physical shock which creates small pits on the edge of the impeller. Each individual pit is microscopic in size, but the cumulative effect of millions of pits over a period of time can destroy a pump impeller. Cavitation can also cause excessive pump vibration which damages bearings, wearing rings and seals. Noise is typically the indication that a pump is cavitating. Other indications that can be seen include fluctuating discharge pressure, flow rate and pump motor current. Excessive pump speed and/or adverse suction conditions will probably be the cause.

Suggestions for avoiding or minimizing cavitation:
 Use the 1.5 multiplier for suction tubing (a 2” pump should have a 3” suction tubing and reduce to 2” at the pump)
  – Note – this could cause excessive pump sizing for CIP flow rate. This is only recommended when cavitation is a concern.
 Use the 7 to 10 diameter rule for straight tubing. No elbows directly into the pump.
 Fluid viscosity kills – stay under 5 feet per second.
 Maintain a static head as high as possible.
 Reduce fluid temperature, although caution is needed as this may have an effect of increasing fluid viscosity, thereby increasing pressure drop. If cavitation is a concern, it is strongly recommended that you contact an engineer to review your process.

Pressure ‘Shocks’ (Water Hammer) 

The term “shock‟ is not strictly correct as shock waves only exist in gases.

The pressure shock is really a pressure wave with a velocity of propagation much higher than the velocity of the flow, often up to 1400 m/s for steel tubes. Pressure waves are the result of rapid changes in the velocity of the fluid in especially long runs of piping.

The following causes changes in fluid velocity:
• Valves are closed or opened
• Pumps are started or stopped
• Resistance in process equipment such as valves, filters, meters, etc
• Changes in tube dimensions
• Changes in flow direction

Most pressure wave problems are due to rapidly closed or opened valves. For example, when a valve is closed, the pressure wave travels from the valve to the end of the tube. The wave is then reflected back to the valve. These waves gradually weaken due to friction in the tube. Pumps, which are rapidly/frequently started or stopped, can also cause some problems. A pressure wave resulting from a pump stopping is more damaging than for a pump starting due to the fact that a large change in pressure continues much longer after a pump is stopped compared to a pump starting. A pressure wave induced as a result of a pump stopping can result in negative pressure values in long tubes, i.e. values close to the absolute zero point which can result in cavitation if the absolute pressure drops to the vapor pressure of the fluid. When designing pipework systems it is important to keep the natural frequency of the system as high as possible by using rigid pipework and as many pipe supports as possible.

Effects of pressure waves:
• Noise in the tube

• Damaged tube

• Damaged pump, valves and other equipment

• Cavitation.

Slip

Slip occurs in PD pumps when fluids passes from the discharge side back to the inlet side of the pump through the pump clearances. It is the difference between the theoretical displacement and the actual displacement. Slip is caused by three factors:

 Viscosity – Slip will decrease as fluid viscosity increases; the
reduction eventually reaches a point called “zero slip”.
 Pressure – Slip will increase with pressure increases
 Clearance – Increased clearances will result in greater slip.
The size and shape of the rotors will be a factor.

If you want more information, contact us by phone or email. 

Pump Pressure Issues – Case Study

Pump Pressure Issues – Case Study

Inconsistent product output? Breaking pipe hangers and ferrules?

These system hammer issues can often be traced back to pump and pressure issues.

A producer of ingredients for human food and animal nutrition was having major issues in their process. They were inducting powdered maltodextrin into their process to form a starch slurry. During the maltodextrin induction process, air was getting into their PD pump. It was then pulled into a centrifugal booster pump that was pushing the slurry vertical 40 feet into a tank. They were experiencing low flow rates (30-60 gpm) and high pressures (>120 psi).

The product was building up in the pump housing seals. Product output was inconsistent. They were breaking ferrules and hangars. They had long periods of downtime. Operators were trying to overspeed the motors on the pumps to increase production rates.

The M.G. Newell salesman recommended that the customer consider a twin-screw pump. Twin-screw pumps can handle highly viscous products such as starch slurries. The design minimizes shearing in the product while still handling high pressures and higher speeds. Most importantly, the pump can handle any air that may be pushed into the line from the powder induction system. The customer removed the PD pump and the centrifugal booster pump and replaced them with 2 twin-screw pumps. They also switched 2” tubing and ball valves to 3” tubing and added an overpressure valve after the first pump.

After one month, the customer loves the new process improvements. They are maintaining a more consistent flow rate of 80-110 gpm and lower pressures of 60 psi. Production increased by 26% with more consistent product and a quieter production area. Maintenance and downtime decreased by 30%.

If you are frustrated with extended maintenance and downtimes, give us a call. We are happy to share our experience with you. Contact one of our associates to see how We Make It Work Better.

If you want more information, contact us by phone or email. 

The Pump Overview Part 2

The Pump Overview Part 2

As we continue the Pump Overview series, let’s review a few basic principles of pumps.
Pressure, friction and flow are three important characteristics of a pump system. Pressure is the driving force responsible
for the movement of the fluid, expressed as pounds per square inch (psi). Friction is the force that slows down fluid
particles. Flow rate is the amount of volume that is displaced per unit time, usually expressed as gallons per minute.
Pumps are typically classified by the way they move fluids. For the sanitary industry, we will only focus on positive
displacement pumps and centrifugal (or rotodynamic) pumps. Positive displacement pumps include single and double
rotary lobe pumps and diaphragm pumps. The table below outlines a few of the basic differences between these pumps.

Centrifugal pump

A centrifugal pump is a rotodynamic pump that uses a rotating impeller to increase the pressure and flow rate of a fluid. Centrifugal pumps are the most common type of pump used to move liquids through a piping system.

A typical centrifugal pump has five basic parts:
1. Casing – also known as the volute, is the outside visible part of the pump. For sanitary processing, the casing is typically a heavy-walled 316L stainless configured in a spiral design to even out flow and minimize turbulence. The end cover is clamped on and can be easily removed for access to the impeller.

2. Impeller – The impeller is the main rotating part that provides the centrifugal acceleration of the product. The impeller can have an open or closed vane. Generally closed vane impellers develop higher pressures but have a lower capacity. Open vane impellers develop lower pressure but have a higher capacity. It is attached to the shaft and rotates inside the casing at the speed of the shaft. The design is balanced to prevent vibration.

3. Shaft – The shaft rotates insides the casing at the speed of the motor and transfers the torque from the motor to the impeller. The shaft is typically made of 316L stainless.

4. Bearings – The bearings support the shaft and keep it in alignment so that it does not wobble inside the casing and prevents it from touching the casing.

5. Seals and/or Packing – The seals are the essential area in terms of hygiene as they prevent the product from leaking back inside the pump or outside of the pump when it is under pressure. Pumps can have either single-seal or double-seal arrangements.

 

How does a centrifugal pump produce pressure?

The fluid enters the pump impeller along or near to the rotating axis and is accelerated by the impeller, flowing radially outward or axially into a diffuser or volute chamber, from where it exits into the downstream piping system.

The velocity of the fluid is also partly converted into pressure by the pump casing before it leaves the pump through the outlet. Pressure is produced by the rotational speed of the impeller vanes. The speed is constant. The pump will produce a certain discharge pressure corresponding to the particular conditions of the system (for example, fluid viscosity, pipe size, elevation difference, etc.).

If changing something in the system causes the flow to decrease (for example closing a discharge valve), there will be an increase in pressure at the pump discharge because there is no corresponding reduction in the impeller speed. The pump produces excess velocity energy because it operates at constant speed. The excess velocity energy is transformed into pressure energy and the pressure goes up.

Centrifugal pumps are typically used for large discharge through smaller heads. Centrifugal pumps are most often associated with the radial-flow type. However, the term “centrifugal pump” can be used to describe all impeller type rotodynamic pumps.

Therefore, the main factors that affect the flow rate of a centrifugal pump are:
 Friction, which depends on the length of pipe and the diameter
 Static head, which depends on the difference of the pipe end discharge height vs. the suction tank fluid surface height
 Fluid viscosity, if the fluid is different than water.

Typically, centrifugal pumps are selected for:

If you want more information, contact us by phone or email.