Rotary Pump Troubleshooting
The next series of blog posts will focus on what operators can do to reduce the time it takes to develop troubleshooting skills. These comments are related to their rotary positive displacement pump technology.
Trouble shooting rotary pumps in systems is a skills that takes some time to develop. We are often contacted about a 'pump problem' without users providing sufficient consideration to changing system dynamics. In almost any pumping system, the pump is the most vulnerable component. However, engineers and operators should be aware that systems dynamics are more frequently the cause of the problem. 'Pump problems' are usually caused by a system component malfunction, inadequate control of the liquid or a change in operating requirements, which burdens the system or pump with conditions in which it cannot perform. Today's post will focus on flow loss or low flow conditions. In future posts will talk about loss of suction and low discharge pressure.
In a positive displacement pump, flow loss is normally accompanied by a reduction in system pressure. Either the pump is delivering less flow, or the system is bypassing it - such as through a defective or worn relief valve or pressure control valve. The pump could be worn and internally bypassing (slipping) flow so that less flow reaches the system. In that event, pump repair will be necessary. A partial inspection of the pump internals will usually provide a good indication of wear condition. Also, if the operating viscosity of the liquid has been reduced (new liquid or higher operating temperature), a rotary pump's rated flow will be slightly reduced and even more so for higher pressure operation.
Sean McCandless Industrial Market Manager Power Generation and Industrial Markets
What’s a Screw Pump?
One of the most common questions we here is, "What is a screw pump?". Unfortunately, screw pump is often a generic term that groups a one, two and three screw pump into one category. Each 'screw pump' operates on the same basic principal of a screw turning to isolate fluid and convey it. However, the mechanical design of each is different. The primary difference in one, two three or multiple screw pumps is the method in which the rotor/pumping element is supported within the casing. 'Screw pump' configurations may include single screw/eccentric screw/progressive cavity, external bearing, timed twin screw pumps, small three screw pumps on lube oil services/machinery support services, large crude oil transfer pumps or even Archimedes-style flood control pumps.
Care to learn more screw pumps? This white paper provides information on when a one, two or three screw pump should be used.
Submitted by: Sean McCandless
Industrial Marketing Manager
BioMass and Process Technology
Colfax Fluid Handling published an article in BioMass Products and Technology entitled, "Choosing a pump". Here are a few excerpts:
"When evaluating pumps for biomass applications, we recommend approaching pump selection from a holistic viewpoint. Several different types of pumps, including positive displacement and centrifugal, can be used in the process as the materials are broken down and converted. Ideally, a pump supplier should be chosen on its ability to offer products that match the specification requirements, as well as knowledge of how the pump interacts with the system and materials."
"The physical properties of the material and aggressiveness through the system also have a significant impact on the pump. Pump materials and coatings, shaft seals and the operating point should be specifically adapted to the pump and system. Be sure to communicate the material and system properties to potential pump suppliers."
We look forward to your comments and hope you enjoy the article!
Best Practices – Two Screw pumps in a Chemical Process Plant
Rob Jordan, sales engineer for Colfax Fluid Handling, recently published a white paper entitled, "Two-screw pumps provide the right stuff for chemical processing". The paper introduces readers to best practices and design considerations for a two-screw pump in a chemical process plant. Two-screw pumps are commonly attached to reactor vessels and used to pump a variety of fluids. Here are a few excerpts -
Two-screw designs in chemical processing applications are capable of flow rates up to 5,000 gallons per minute, differential pressures that exceed 1,000 psid, product temperatures up to 750F and product viscosity in excess of 1,000,000 cP, making them a very robust piece of machinery. They are capable of handling a variety of process conditions that exist in the chemical manufacturing and processing industry.
Two-screw pumps offer extremely low NPSH requirement (NPSHR). This allows for pumping under a wide range of difficult suction conditions, liquids and operating scenarios. A two-screw pump offers users low NPSHR because the suction design has low resistance to flow of the liquid entering the pumping chambers; with higher resistance to flow you generate a larger pressure loss and increase the likelihood of cavitation. Specific design feature of a two-screw pump that reduce a liquids resistance to flow are: 1) divided flow paths that split the incoming fluid to opposing ends of the case; 2) large cross sectional area of the suction passageway: 3) lower axial speeds within the pumping chamber which are a function of the pump rotational speed and selected screw pitches.
We hope you enjoy the article and look forward to your feedback!
3 Screw Pumps and the Laws of Physics (Hydrodynamic Film Theory)
As many or you know, in the 1920’s the Swedish Engineer Carl Montelius (the MO in IMO) established the mathematical design for the 3 screw pump as we know it today. Those of us that do selections of 3 screw pumps here at Colfax are very familiar with the WIPS program which provides us with a quick selection and full detail of performance data.
There are multiple criteria that must be evaluated in the program to assure selection of a proper and reliable pump. One value that is figured into every selection in the program is called the Sommerfeld Number, named for the 19th century Prussian theoretical physicist Arnold Johannes Wilhelm Sommerfeld. Nominated a record 81 times for the Noble prize, pioneer of X-ray wave theory, as well as quantum physics, I guess we could consider him the real “Sheldon” of his day for any of you that have watched “The Big Bang Theory” on CBS.
Above (L to R): Arnold Johannes Wilhelm Sommerfeld, "Sheldon"
The Sommerfeld Number is a dimensionless quantity typically used in hydrodynamic lubrication analysis (journal bearing theory). In brief, it assures us that the idler rotor OD’s are riding on a sufficient film of fluid thus avoiding direct rubbing contact with the pump housing bore. It is defined by the following equation.
Where:
S is the Sommerfeld Number or bearing characteristic number
r is the shaft (journal) radius
c is the radial clearance between the journal (shaft) and the bearing (housing bore)
μ is the absolute viscosity of the lubricating liquid
N is the rotating speed of the shaft in revs/sec
P is the load per unit of projected bearing area
For the pump to perform reliably, WIPS must calculate a sufficiently high Sommerfeld number as one of the criteria to approve a selection. Fortunately the formula is pretty straight forward, not calculus, and taking a short look at it you can see the parameters that help or hinder the pump performance
(r) The shaft radius - The larger the diameter of the idler rotor the better. This is effectively true because the surface of the screw is passing the surface of the housing bore at a faster speed for a given rpm
(c) The radial clearance – The tight clearance of the Imo pump increases the Sommerfeld number
(μ) The absolute viscosity of the lubricating liquid – The higher the viscosity the better. We do not think much about the difference between 1 or 2 cSt, but once you place the value in the formula you see that the value of 1 cuts the Sommerfeld number in half, a big difference
(N) The speed of the rotating shaft in revs/sec – The faster the better
(P) The load per unit of projected bearing area – Basically this is saying that the longer the rotor and housing (12D vs. 3D) the better.
As a practical example of hydrodynamic film theory as discussed above, just consider water skiing, and the effect of increasing speed.
At 2 mph you can not get on top of the water, 20 mph all is good, 50 mph you no longer need the skis, if you are really good and your feet are large enough.
Rich Meighan
Director Product Sales
Power Generation and Industrial Markets
Zenith PEP II Pumps excels in the growing bioplastics market
5 questions on BioPlastics with Zenith Sales Representative - Peter Yeoung
What are bio-plastics?
You have likely seen some a bio-plastic in use on consumer products located on your grocery store shelf. The most likely is the biodegradable potato chip bag from Frito Lay. This product led to a major campaign and effort to educate consumers about the contents of packaging material. Other companies like Proctor and Gamble and Papermate also use bioplastics in their packaging.
In the article, “Consumers Push Plastics Industry to Find Bio-Based Solutions”, analyst Kurt Furst of The Freedonia Group forecasts this market to grow at 35% and exceed $5B by 2018. This however, remains at just a tiny fraction or 0.1% of the total global plastic demand
By definition: A bioplastic or organic plastics are a form of plastics derived from renewable biomass source, such as vegetable oil, corn starch, pea starch rather than fossil fuel plastics which are derived from petroleum. Some, but not all, bioplastics are biodegradable.
Describe the Colfax Fluid Handling application?
In a bioplastics application, the Zenith PEP pump function is generally described as an extrusion pump located after the extruder and filter. The pump supports the extrusion process metering additional bioplastic to the extruded material to ensure a consistent repeatable thickness throughout.
Manufacturers use the Zenith pump to ensure very accurate thickness. If the material is not extruded uniformly, you will negative downstream effects in the thermal forming process resulting in lost product and money.
What should a design / process engineer consider when evaluating pumps for this application?
There are three considerations. The first and most important is the accuracy of the pump. The more accurate the pump the more consistent thickness the material will be in the process. The second is the dynamics of the process. Placing a Zenith PEP pump after the extruder will allow the pump to build pressure in the system instead of the extruder. When the process builds pressure through the pump there is less stress on the bearing generating longer operating life for the extruder. Finally, the differential pressure of the extruder has been reduced and this enables greater output at the same speed.
What models do you typically sell into this application?
PEP II 100cc per revolution and 175cc per revolution
Who are some of the OEMs that you have worked with?
My customer base and focus is primarily Chinese OEMs – examples include ShanTou Kica, Dongguan HongHao, Davis Standard (major oem for plastic extrusion) and American Leistritz
Colfax Offers Aftermarket Replacement Stator for Wastewater Pumps
Colfax Corporation, a global leader in fluid-handling solutions for critical applications, announces its new Alldur® stators, developed through the company’s Fluid Handling business platform. Alldur stators are designed specifically to meet the aftermarket replacement needs of North American wastewater treatment plants.
Stator replacement is one of the major contributors to total cost of ownership of a progressing cavity pump. The new Alldur stator material dramatically extends the service life of this major wear part and offers a rapid payback to wastewater plant operators.
“The new Alldur stators provide up to three times the service life of existing progressing cavity pump stators, stand up to dynamic loads and offer high-impact resilience,” said Todd Kierstead, Product Specialist, of Colfax Fluid Handling. “This allows operators to reduce downtime and increase maintenance intervals.”
The elastomer’s new proprietary chemical composition make Alldur stators capable of handling dynamic loads, providing high-impact resistance to mechanical wear, even when used in applications with extremely contaminated, high-solids content wastewater. This significantly reduces stator wear and helps to repel solids with little or no damage to the stator, which is designed to assume its original shape.
Alldur stators are manufactured at Colfax Fluid Handling’s Allweiler facility in Bottrop, Germany
When Energy Subsidies Will be No More in the Middle East – The Day is Coming Sooner than You Think!
Since the late 1970’s, the countries bordering the Persian Gulf have enjoyed subsidized energy prices for fuel and electricity. This national assistance program supported the development and growth of the economies in each of the Gulf Cooperation Council (GCC) states. In practice, over the short term, this was a beneficial initiative, but four decades later global economic factors have dramatically changed. Early on crude oil and power generation feed stocks were inexpensive commodities, so subsidizes imposed little strain on the Persian Gulf state economies. That has all changed! Crude oil and finished product market prices have risen sharply by as much as ten fold. Ongoing subsidizes for these vital, everyday needed energy sources are now putting a huge financial strain on the GCC countries. Profits which are obtained from increased oil prices are quickly siphoned off and lost to fund these subsidies. This problem is exacerbated by the ballooning populations of nationals and expats residing in these territories. More people demand more energy. An unfortunate side affect of these subsidies has been the entrenched mindset in the region that responsible energy use is a problem that the rest of the world contends with, but not the GCC: energy prices are dirt cheap here; we have all that we need!
Both of these factors are now compelling the governments of the GCC states to make changes. The attitude towards the true cost of providing electricity and gasoline, and its responsible use, now needs to be borne by the people. To this end, subsidies are now being reduced in some countries by as much as 30% and this trend will only continue. As has been the case with the United States, a Great Awakening is starting to take place in the Middle East. Energy sources are still plentiful, but their increased value is now encouraging individuals to think differently about how they are used. Energy efficiency is now starting to be talked about in all sectors like never before. This responsible attitude is needed to support the GCC’s long term ambitions to cultivate other domestic industries to increase the local value added and employment opportunities, thereby keeping more profit within the region. To achieve this goal, enormous investment will be needed. The funds will come from the energy sector; therefore, the subsidies must decline and ultimately they will need to be phased out to make this a reality. Individuals and businesses that acknowledge this inevitable change will start to reprogram their behavior and processes to be more profitable now and ultimately solid and sustainable in the future.
So how does all this relate to the world of fluid-handling and pumps? It’s quite simple, engineers in the Middle East need to start making better technical choices based on energy consumption! In the not so distant future, this increasing overhead cost will erode your profitability. Power saved is profit you get to keep now and for the foreseeable future. It’s a potential investment source at your fingertips that you can infuse into the upgrading of your operations.
Drop me a comment. I would be interested to hear about some of the processes that you feel could be present some worthwhile savings. I would be happy to share some of my experience with you.
Mike Moore - Director, Global Oil and Gas Marketing
Going from Smart to Intelligent – What Your Operators Really Need!
For decades end users have faithfully equipped their plants with a wide array of telemetry devices linked back to a central process data control system, giving them a real time indication of the state of their process. To ensure maximum uptime of their facility, while at the same time looking to avoid a catastrophic equipment failure, they exercised similar care in outfitting their critical rotating equipment with a wide array of transducers, probes, switches, transmitters and the like. This two pronged approach gave them the process control that they needed, helping to minimize unplanned shutdowns and costly equipment repairs, as compared to past “run-to-failure” operating philosophies. Improved process efficiency and sustainable production rates, as well as cost avoidance, provided the justification to invest in these electronic tracking and surveillance systems. From a business standpoint it was a smart choice, but with a little education, a dash of creativity and some reconfiguring it could be transformed into an intelligent one!
Intelligent Systems – instrumented processes that help make you money. Sound far fetched? Not really. In most plants the bulk of the infrastructure exists and the data is largely available. It’s a potential money making opportunity that just needs to be harnessed. Imagine an Intelligent System that can, in a real time manner, assess what a particular piece of rotating equipment is doing from a work load standpoint versus what it is really capable of doing. Based on this analysis a series of questions or options could be displayed to the operator that he or she could either act upon or say thanks, but no thanks to. Think of the power that this could put at the operator’s fingertips. The control room personnel can now focus their full attention on overseeing the process without needing to be rotating equipment experts. Operational changes could be made more quickly minimizing the potential misuse of equipment under their control. In essence, the Intelligent System becomes their facility copilot, promoting them with safe options to make their jobs easier. It’s like having a virtual OEM on staff 24/7.
Now that I’ve opened your eyes to the possibility of Intelligent Systems, let’s hear your ideas. Get your synapses firing! Think of the processes that could benefit from this. As users, all you need is a collaborative OEM to help infuse some of their knowledge and expertise into your control system to make this a reality.
Mike Moore
Director, Global Oil and Gas Marketing
Colfax’s PurLube System – Solving Water Contamination Problems in Lubrication Oil
If you’ve worked in a steam turbine driven power plant you know how difficult it is to keep water out of your machinery and lubrication systems. When water finds its way into your lube oil system, it increases the risks of corrosion, wear and premature failure. There are many articles available that discuss water’s impact on bearing life performance and system reliability including Water – The Forgotten Contaminant by Mark Barnes from Noria Corporation. It provides a good overview of the harmful effects water can have on a process.
So if you have water in your system, what can you do to remove it? In almost all cases, the answer is “it depends” as there are multiple solutions available and we recommend that you consult with manufacturers to understand the tradeoffs that you will make. Also, filtration technologies should not take the place of a complete system analysis to diagnose the root cause. In the rest of today’s post, we’ll focus on the Colfax PurLubeTM system comparing its features and benefits to alternative water filtration technologies.
The Colfax PurLube System
A PurLube system is commonly installed in a kidney loop off the main lube oil console. In a kidney loop, the PurLube is able to pull lubrication oil from the system and return it after treatment.
Once the oil enters the PurLube, it is heated to 180°F without causing thermal or oxidative stress to the oil. Next, a venturi draws air into the oil creating small air bubbles. When the air bubbles mix with the heated stream of lube oil, the volume and surface area of the bubbles expand causing any moisture that contacts the bubbles’ surface to evaporate into the heated air inside the bubbles. The oil stream is then passed through a settling tray allowing the bubbles to come to the surface and break, allowing the formerly entrained water to simply escape as evaporating water vapor.
The ‘water entrapment principal’ is comparable to relative humidity. The amount of water in air (grams H2O per kilogram of air) increases with temperature. For example, air will entrain 30 times more water at 180°F than it will at 80°F.
The PurLube removes all three forms of water contamination in lube oil - free, emulsified and dissolved – to lower than 100ppm. Additionally, the discharge does not contain any oil or emulsion and maintenance is relatively low because the system only has one moving part, the oil recirculation pump.
Finally, the PurLube system is an OEM component available in steam turbine lubrication systems built by a major US based turbine / generator manufacturer.
Machinery Lubrication provides a good summary of the technologies available for water filtration. There are three other types of water stripping systems available today - centrifuges, coalescing filters and vacuum dehydrators.
As outlined in the Machinery Lubrication article, the centrifugal separator is the earliest design of an oil water separation system and removes both free water and emulsified water. The principal of the centrifuge is to separate the oil’s heavier elements by spinning the oil to create “G’s”. The technology works well when you have a significant difference in specific gravity between the two fluids.
A centrifugal separator, however, does not remove dissolved water and the discharge must be treated to insure that hydrocarbons do not enter the ground water or municipal water treatment systems. Also, a centrifuge will lose on average 1 or 2 gallons of lube oil per day in the discharged emulsion. At an average price of $30.00 / gallon, this loss can represent from $10,000 to $20,000 per year.
Coalescing filtration systems represent an improvement in energy consumption and maintenance when compared to a centrifuge and there is less loss of the expensive lubricants. However, there is a significant loss of filtration and separation efficiency if there is any emulsion in the lube oil. The coalescing filter system also has no effect on the removal of dissolved water in the lube system. The most significant operational cost can be the periodic replacement of the coalescing cartridge elements. This annual cost can easily exceed the initial cost of the complete system.
A vacuum dehydrator system lowers the partial pressure and thus the temperature at which water boils. Like the PurLube, a vacuum dehydrator will remove free, emulsified and dissolved water. However, there are several factors that set these systems apart such as:
- The vacuum dehydrator is a much more complex system having a significantly higher initial cost.
- The annual energy consumption, maintenance and consumable costs for these systems can approach the initial cost of the installed system.
- The separation efficiency of these systems may be compromised with higher viscosity or synthetic oils.
If you’d like more information or would like to discuss a specific application please contact Colfax Applications Engineering, Todd Kierstead (Product Specialist) or Larry Nowakowski.
Larry Nowakowski
Marketing Manager Power-Gen / Energy for Colfax Americas