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
5 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 HandlingCrescent Internal Gear Pumps for Fuel Injection Application
The U.S. Energy Information Administration released their Annual Energy Outlook in December which forecasts that by 2035, 83% of new capacity additions will be from either natural gas or renewable energy.
The forecast provides a strong correlation to government and public sentiment on energy.
The unpredictable nature of renewable power generation in select cases requires backup generation support from aero derivative turbines or other smaller scale industrial turbines. How these two fuel sources coexist remains a work in progress. Aero turbines have gas as their primary fuel system and the option of liquid fuel for backup. Of course, these systems can also be used for traditional generation such as peak generation.
A large manufacturer of aero derivative turbines recently chose Colfax America’s CIG pump line for their fuel injection pumps. A fuel injection pump delivers fuel directly to the gas turbine for combustion. The CIG pump is a Crescent Internal Gear pump with multiple stages good for applications with high pressure (4000 psi or 275 bar) or moderate pressure/low viscosity applications. It provides a user with smooth pulsation free flow, a vital feature for today’s engine requirements. 
The chart to the right is a sample flow/pressure curve for the CIG pump, you will note that with a viscosity of 4.1cst, the flow output has less than a 15% change in flow over the pressure range 25psid – 1,600psid.
Sean McCandless
Sean McCandless
Market Manager- Power Generation
Colfax Corporation