Trouble shooting tips – Low Discharge Pressure
I've gotten away from my series on diagnosing pump problems. Hopefully, you've been able to read and digest previous posts. For this post, I'll discuss the issue of low discharge pressure. I look forward to your emails and continued discussion on these topics.
Low discharge pressure can be caused only by loss of flow. Pump discharge pressure is caused ONLY by the system's resistance to the flow provided by the pump. Either the pump is not providing the flow expected, or the system is not offering expected resistance to that flow. It is possible that flow into the pump is being restricted (cavitation or suction starvation). This phenomenon is usually accompanied by noise and vibration. Or, it could be that the pump is not producing its rated flow (pump worn or damaged), or that the pump flow is bypassing rather than being delivered into the system as intended (open, improperly set, damaged or worn discharge system valve). If the pump is relatively new and not being used in abrasive service, it is most probable that discharge flow is bypassing. The most likely paths for such unwanted bypass are the system pressure relief valve (sometimes built into the pump), a bypass pressure regulator leaking (typical of a fuel oil burner system), an inadvertently open bypass valve, or any of these valves having worn valve seats, incompletely closed stems, incorrect signal control or broken springs.
Many pumps can receive a quick, though incomplete, inspection in place without disturbing piping or pump alignment. If the pump does not turn over by hand or with a little leverage assistance and in a smooth manner, the pump itself may be the problem. If one or more of the pumping elements can be visually inspected without major tear down or pump removal, do so. Enough wear to cause a pressure reduction (flow loss) should be readily visible.
It is sometimes difficult to determine if a valve is bypassing when it shouldn't, especially if the valve is built into the pump. It is probably best to remove the valve, do a partial valve dis-assembly and examine the mating valve seat surfaces or seat seals for wear or damage. Check any spring to be sure it is not broken. Work the valve mechanism manually if possibly to detect any binding or galling.
If the problem has still not been identified, be sure the pump river speed is being achieved and that the pump shaft is actually rotating at is correct speed. These conditions must be met, especially in a new system start up.
Sean McCandless Industrial Market Manager Colfax Fluid Handling
Not sure what type of pump you need?
Don't be afraid.
There are many factors when choosing a pump - pressure, flow, liquid properties, accuracy, shear and power requirements to name a few. Imo pump recently introduced one of the most complete pump specification sheets on the market. If you're not sure which pump type you need, start here and we'll work with you to choose the best product for your application.
Sean McCandless Industrial Market Manager Colfax Fluid HandlingWhen should I use a One, Two or Three Screw Pump?
I had previously posted a link to a white paper written by Rob Jordan in which he talks about some of the unique benefits and operating characteristics of 'screw pumps'. Hopefully you've had a chance to read this article and learn a little bit more about the products that we offer.
Today, I'd like to provide with readers a quick reference guide on when to use the products that Colfax Fluid Handling offers. This summary is referenced from the 2008 American National Standard for Rotary Pump types and Nomenclature, Hydraulic Institute. Note, a timed multiple screw pump is also known as a two screw pump and an untimed multiple screw pump is also known as a three screw pump.
| Progressing Cavity | Timed Multiple Screw Pump |
Untimed Multiple Screw Pump |
units | |
| Flow | 3750 | 12000 | 5300 | gpm |
| Pressure | 1500 | 1500 | 4500 | psi |
| Viscosity | 2.0 | 4.5 | 1.0 | Million SSU |
| Solids | 3.5 | 1/32 | Clear | in |
| Temp | 400 | 700 | 500 | °F |
| Self Prime Dry | Y | N | N | |
| Self Prime Wet | Y | Y | Y | |
| Dry Running | N | Y | N | |
| Reversible | Y | Y | Y (special) | |
| Abrasive Handling | Excellent | Good | Good | |
| Shear Sensitive | Excellent | Good | Good | |
| Pulseless | Excellent | Excellent | Excellent | |
| Horsepower Range | 0.1-200 | 5-2000 | 1-1000 | BHP |
As always, a thorough discussion with an application engineer is recommended if your application falls outside of these parameters.
There's a lot more to it then this and we're encouraging readers to contact us and discuss a lunch and learn session. What's better than a free lunch and a little education?
Sean McCandless Industrial Market Manager Colfax Fluid HandlingProgressing cavity pumps for explosion emulsions
This falls into one of the more interesting applications we see - pumping of ammonium nitrate. We commonly see these applications in the mining market. Progressing cavity pumps are the pump of choice here because of the low shear that they apply on the product as well as the high viscosity of the explosive liquid.
Why is the right design important or what are some of the hazards users might experience when pumping ammonium nitrate?
- Deadhead pumping which is caused by cooled down emulsion explosive forming a plug or by a foreign object
- Dry pumping which generates excessive heat and may result in ignition of explosive residue
These are just some of the reasons the Allweiler branded pumps are the pump of choice. Allweiler pumps applied in this application are intrinsically safe and have met (or can meet) the necessary hazard operation reviews required.
Download your copy of our progressing cavity pump brochure, fill out the application data sheet and get the right pump for your application or contact us to learn how we can help.
Sean McCandless Industrial Market Manager Colfax Fluid HandlingUh oh…my pump didn’t last as long as I think it should
The next section on our series on diagnosing or understanding pump problems, will focus on rapid pump wear.
Rapid pump wear is caused by either abrasives in the liquid or operation under conditions for which the pump is not suitable, such as excessively low viscosity or excessively higher pressure or temperature. If abrasives are a normal condition of the pumping application, as in slurry pumping, then pump wear will be a fact of life, and the best that can be done will include pump and drive speed selection that provides the best economic evaluation over the pump life cycle. While requiring bigger displacement and more expensive pumps, slower operation on abrasive service often pays back far beyond the initial purchase cost differential.
Wear due to abrasives in the liquid is a function of speed raise to a power usually betwen 2 and 3. If the abrasives are deliberately introduced, as when fuel oil additives intended to reduce boiler corrosion are brought into a system, they should be injected downstream of any liquid recirculation to insure that they do not go through the pump. Obviously, if abrasive foreign material is not supposed to be present, strainers or filters should be employed wherever possible and practical.
Rapid wear is sometimes not wear in the sense of a non-durable pump, but rather a catastrophic pump failure that occurs very quickly. Looking at the pump internal parts alone can frequently not provide much help in setting a direction to search. So, it is important to know what was occurring in the time period immediately preceding the detection problem.
Often, pump manufacturers offer a checklist designed to help you understand potential causes to failure. Contact your supplier today to discuss your issue and what supporting information they have available.
I'm also pleased to announce that our IMO pump brand has an updated Application Data Sheet. The data included in the online tool enables our engineers to answer your questions and projects request quickly and accurately. Moreover, you can consider products from the entire Colfax product portfolio.
Sean McCandless Industrial Market Manager Colfax Fluid HandlingThoughts and Comments from the Power Gen Show in Las Vegas
The Colfax Fluid Handling team was on display at the Power Gen show in Las Vegas. If you attended the show, hopefully you had a chance to come by and say hello. Overall, I thought the show attendance was greater than the 2009 Las Vegas show, but less than the 2010 show in Orlando.
The quality of leads generated at the show was, however, solid and the Colfax team was fortunate to talk with people who -
- Had problems with water in their lubrication Oil (recommend the ThermoJet or PurLube)
- Was interested in pumping sulfuric acid within the environmental system of his plant (recommended the Zenith metering pump)
- Was interested in using a progressing cavity pump in a vertical configuration to save space in his sump (recommended the Allweiler branded progressing cavity or Emtec pump)
- Needed to understand how to size three screw pumps for a fuel oil plant that they were building in the Middle East (recommended the IMO or Allweiler branded three screw pump)
These were only some of the applications that we discussed with show attendees. These leads also show the diversity and flexibility of the Colfax portfolio and the global coverage that we offer our customers.
Finally, we always welcome the opportunity to conduct a lunch and learn seminar for your associates. We offer topics such as the basics of centrifugal vs. positive displacement pumps, design and considerations for lubrication oil systems and three and two screw pumps benefits and design considerations. If you're interested, let me know.
Sean McCandless Industrial Market Manager Colfax Fluid Handling5 Questions – Designing Lubrication Oil Systems for Power Generation Plants
We are fortunate to work with a great team from Baric who provide us with deep expertise in engineered system construction for the Power Generation, Oil and Gas and Industrial markets. I recently conducted a 5 question interview session with Darren Godsmark, Sales Director. This interview provides a good overview of how Colfax is challenging OEMs to think about their system designs and consider alternatives in system construction and configuration -
Contact us if you're interested in designing a better system.
Baric is well known as a designer and manufacturer of unique packaged units for the rotating machinery industry. The Power Gen industry, however, primarily uses pre-engineered or “build to print” packages. Can you provide some example of your ability to showcase Baric’s design skills in the Power Gen market?
Yes, there are several examples. In fact, we have a design contract to design a skid package for a particular sized turbine for a major global Power Gen supplier.
One of our best examples, however, was a project in which we provided Lube Oil Systems (LOS) for 50Hz and 60Hz turbo-gen sets. It was essentially a “build to print” contract, but we identified a number of improvements that could be made on the systems, which we relayed to the customer.
We’re quite proud of our ability to add value to a customer’s projects by drawing on experience and know-how.
Was the customer interest in finding out about the improvements?
Absolutely. We were invited to participate in a number of seminars – mini-Kaizens, actually, with their design team.
What was the focus of the seminars?
There were essentially three considerations:
- Review and update the global specifications for the lubrication oil system
- A detailed review of main sub-supplied equipment, such as pumps, motors and control valves
- The physical layout of the lubrication oil system
What were the biggest challenges the seminars presented?
The first two were fairly straightforward as the assembled teams worked through the original global specifications. We discussed each element in detail – from material selections of reservoirs and piping to potential suppliers for the main buy outs. We then created a revised final version based on a combination of best practices, shared field experiences and sub-supplier evaluation.
The real challenge came in the design of the LOS itself. Both the 50Hz and 60Hz Turbo-Gen sets had to have the same physical footprint. Site interface points had to be located in the same places. Multiple Lube Oil Cooler options had to be designed without changing the footprint. This included the remote air cooled heat exchanger, plus a single plate & frame water cooled heat exchanger LOS and a dual (duty and standby) plate & frame water cooled heat exchanger, both mounted on the LOS. Both required European (CE) and North American instrumentation installation, as well as AC and DC motor installation. Working together, the customer’s team and the Baric team were able to solve these issues.
Do you think the exercise was a success?
Most definitely. By achieving the design brief as describe above, it gave the customer the option to provide the LOS as a stock order item, based on local requirements, for any area of the world in which they marketed. But for us, the biggest validation was the number of contracts we received by using this design, supplying machinery in Asia, the Americas and Europe.
Sean McCandless Industrial Market Manager Colfax Fluid HandlingWhat to do about excessive power usage
In our continuing series on Rotary Pump Troubleshooting, we'll take a look at the condition of "Excessive Power Usage". As always, consult the factory or your local service representative for additional assistance.
Excessive power consumption can be caused by either mechanical or hydraulic problems. For rotary pumps, the pump power requirements are directly proportional to pressure and speed. If either has increased, the required input power will increase. Power required will also increase if the fluid viscosity has increased. This can happen if the liquid has been changed to something new or the liquid operating temperature has been reduced. Some liquids (grease, for example) are shear sensitive and can become more or less viscous with shear (pumping action) as well as undergo permanent viscosity change from shear over time.
Mechanical causes of high power usage include bearing wear out, pumping elements rubbing (a situation that can lead to pump failure), very bad shaft alignments and poor pulley alignments for belt drive arrangements.
Sean McCandless Industrial Market Manager Colfax Fluid HandlingZenith 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
Calculating Cost of Ownership
In your company, what criterion drives your purchasing decisions? Does first cost win or do you evaluate the life cycle cost? Does the purchasing manager win with the low priced bid or does the diligent engineer who has thoroughly calculated all costs and scenarios win? The answer – it likely depends and each scenario is different. At Colfax, we focus our discussion on total cost of ownership as our products have value beyond the purchase price and are designed to last for years once properly installed.
As stated in the Hydraulic Institute/EuroPump guidebook, the lifecycle cost of pump can be calculated by:
LCC = Cic + Cin + Ce + Co + Cm + Cs + Cenv + Cd
Where
- Cic is the initial cost or purchase price
- Cin is the installation and commissioning costs
- Ce is the energy costs
- Co is the operating costs
- Cm is the maintenance costs
- Cs is the downtime costs
- Cenv is the environmental costs (leakage losses and permit violations)
- Cd is the decommissioning costs
One area where a firm can lower its first cost of positive displacement pumps is to properly size the pump to the requirements of the systems. Frequently, we see companies oversize their pumps in an effort to plan for future expansion. Our recommendation is to be realistic in your expectations as you will likely waste a lot of energy, time and money compensating for that pump. Pump energy consumption and maintenance issues are 52% of the total cost of ownership.[1]
If you have already installed your system, watch the bypass valve and see if it is continually lifting to return fuel back to the system. This can be an indication that your pump is oversized for the system requirements. If you do a better job of matching the flow requirements of the system with the delivered flow of the pump, you will lower the brake horsepower required to operate the pump and your energy costs.
If you’d like additional information on this topic, the Hydraulic Institute Division, Pump System Matters, offers a class on Pumping System Optimization: Opportunities to Improve Life Cycle Performance. You may also want to experiment with the free downloadable modeling tool offered by Pump Systems Matter.
Our application engineers are ready to help you answer your application and total cost of ownership questions. We look forward to hearing from you.
[1] Hydraulics Institute www.pumps.org