As a FGD pump supplier, I’ve spent the last seven years troubleshooting our own pumps in power plants across the Midwest, and let’s be honest—most operators reach for the manual only when a pump locks up mid-cycle. FGD (Flue Gas Desulfurization) pumps don’t get the same hype as turbines or baghouses, but they’re the unsung workhorses that keep sulfur dioxide out of our air. A well-troubleshooted FGD pump doesn’t just run smoothly; it cuts your annual maintenance costs by 20% or more, per data from the Electric Power Research Institute (EPRI). Today, I’m walking you through the step-by-step troubleshooting framework I share with every client—no jargon, just the on-the-ground tricks I’ve learned fixing thousands of these pumps. FGD Pump
First, let’s set the stage: FGD pumps handle wet, abrasive slurry, usually a mix of water, limestone, fly ash, and residual sulfur compounds. That’s way harsher than the clean water your home sump pump moves. So most issues tie back to abrasion, clogging, or minor calibration slips that turn into big problems. The first rule of troubleshooting any FGD pump? Start simple before tearing into the equipment. I see operators skip this all the time—they jump straight to taking the pump apart when the discharge pressure drops, when half the time it’s a closed valve or a clogged strainer. Let’s break this down into a flow that works for on-site teams.
First, the pre-inspection: a 10-minute walkaround that catches 40% of issues before they escalate. I start with the basics that don’t require tools. First, check the power supply and control panel. It sounds silly, but a tripped breaker or a loose wiring connection is the number one reason a pump won’t start. Last year, I got a call from a plant in Ohio that swore their FGD pump had “crashed” during a limestone feed cycle—turns out a maintenance tech had bumped a 480V breaker while replacing a fuse on a different unit. Next, check the valve positions: make sure the suction valve is fully open (a partially closed suction valve cuts flow by 50% and causes cavitation, one of the biggest FGD pump killers) and the discharge valve is at the correct opening percentage. I always keep a small log book for this—jotting down valve positions, pressure readings, and ambient temp every week helps spot patterns, like a suction valve that slowly gets partially clogged with scale over three months.
Next, after confirming power and valves, move to the pump’s core metrics. Pull the current draw from the control panel. FGD pumps have a rated full-load amp (FLA) number stamped on their nameplate, usually 125A for a 100HP FGD pump. If the current is spiking 15-20% above FLA, that’s a red flag. Common causes here include impeller clogging with limestone scale or broken solids, misaligned pump and motor shafts, or slurry viscosity that’s off. FGD slurry viscosity is critical—if the limestone ratio is too high, the slurry thickens like honey, forcing the pump to work harder and spike current. I once helped a plant in Indiana that had adjusted their limestone feed rate to cut sulfur emissions, but they didn’t adjust the pump speed to match, leading to 30% higher current and a impeller replacement every six months. The fix? Adding a variable frequency drive (VFD) that matches pump speed to slurry demand, which also cuts energy use by 30%. That’s a win-win.
If current is normal but flow or pressure is low, that’s usually a suction side issue. I call this the “no suction” problem, and it’s almost always related to net positive suction head available (NPSHa), or the pressure at the pump suction to keep slurry flowing. FGD pumps need at least 10-15 feet of NPSHa, because slurry has a higher density than water. If your suction line has a leak, that introduces air into the system, which causes cavitation—small bubbles that form and collapse on the impeller, wearing holes in it in as little as 3 months. I once tested a pump that had 20% lower flow, and found a small leak in the suction line that was letting in air; fixing the leak brought flow back to 95% of rated capacity, no impeller replacement needed. Another common suction issue is a clogged suction strainer or inlet. FGD slurry has small solid particles, and over time they build up on the strainer, restricting flow. I recommend cleaning strainers every 500 hours of run time, or setting up a differential pressure alarm on the suction strainer that alerts operators when it’s clogged.
If flow and pressure are normal but the pump is making noise, that’s often mechanical. FGD pumps can make three key noises to listen for: a high-pitched squeal, a low grinding hum, or a rattling vibration. The squeal is almost always cavitation—when those air bubbles I mentioned earlier collapse on the impeller. The fix here could be adjusting the suction pressure, cleaning the strainer, or even adding a smaller impeller if your pump is oversized for your current flow needs. The grinding hum is abrasion—slurry particles wearing away the impeller or volute. FGD pumps have replaceable wear parts, but if you hear grinding, it’s a sign that your impeller or volute is already worn past the point of efficient operation. I always tell operators not to wait for the pump to fail completely—if you hear grinding, schedule a wear part replacement during the next scheduled outage, not an emergency shutdown that can cost tens of thousands in lost power generation. The rattling vibration is usually misalignment between the pump and motor. Over time, pipe stress from the suction and discharge lines can shift the pump’s position, leading to misalignment that wears out the shaft seal or bearings prematurely. I recommend doing a shaft alignment check every 1,000 hours of run time, using a dial indicator—most plant maintenance teams have these tools, and it takes about an hour.
Another common issue I troubleshoot is seal leaks. FGD pumps use either mechanical seals or packing seals, depending on the application. Mechanical seals are more common on newer units, because they require less maintenance, but they can leak if the seal water pressure is too low. Seal water keeps the seal face cool and flushes away slurry that gets past the seal. If seal water pressure is below 20 PSI, slurry will creep past the seal and cause it to fail. Packing seals, older style, require adjusting the gland bolts—too tight and they wear the shaft, too loose and they leak. A good rule for packing seals is to have three to five drops per minute leaking out; that keeps the seal lubricated without wasting water. If you’re seeing more than that, or a steady stream of slurry leaking from the seal, that’s a sign you need to replace the packing or adjust the gland.
Wait, let’s talk about a mistake I see every day: ignoring temperature readings. FGD slurry can heat up from friction as the pump runs, and if it gets too hot, it vaporizes, leading to cavitation. I always have operators check the pump casing temperature against the ambient slurry temperature. A delta of more than 10 degrees F means the pump is overworking, usually from clogging or misalignment. Last year, a plant in Michigan had their FGD pump running at 180 degrees F, and they couldn’t figure out why their impeller was failing every 4 months. Turned out the pump’s cooling system (for the seal and bearing) was clogged with scale, so the pump was overheating. Cleaning the cooling lines brought the casing temperature down to 120 degrees F, and impeller life extended to 18 months. That’s a huge cost savings right there.
Now, if you’ve gone through all these steps and can’t find the issue, it’s time to check the impeller and volute. But only do this if you’ve ruled out all the simpler stuff—pulling an impeller is a 4-6 hour job, and you don’t want to do that for a tripped breaker. When you do take the pump apart, look for signs of wear: impeller vane erosion (small, rounded grooves on the vanes), volute casing wear (scored spots on the inner wall), or clogged passages with solid material. If the impeller is less than 50% worn, you can often machine it to smooth the edges, which restores flow. If it’s more than that, replace the impeller with the correct material—we recommend high-chrome iron for most FGD applications, because it resists abrasion far better than cast iron. I always tell operators to keep a spare impeller and seal on hand, so you can do an emergency swap in 2 hours instead of waiting for parts and shutting down for 8 hours.
Let’s wrap this up with a quick troubleshooting checklist you can take to your next shift. Print this out and tape it near your FGD pump:
- Pre-Start Check: Verify power is on, breaker not tripped, control panel displays normal voltage
- Valve Check: Suction valve fully open, discharge valve set to 80-90% open (not fully closed!)
- Metrics Check: Record current draw, compare to FLA; current >110% FLA = investigate clogging/misalignment
- Flow/Pressure Check: Low flow? Check suction strainer, suction line leaks, NPSHa level
- Noise/Vibration Check: Squeal = cavitation; Grind = abrasion; Rattle = misalignment
- Seal Check: Mechanical seal pressure ≥20 PSI; packing seal leaks = 3-5 drops/minute
- Temperature Check: Casing temperature within 10°F of slurry temp; over temp = check cooling system
And here’s the final tip from 7 years in the field: preventive troubleshooting works better than reactive. Keep a log of every reading—current, pressure, temperature, leak rates—and check it monthly. If you see current rising 5% every two weeks, that’s a sign your impeller is slowly wearing, not a full failure. Catching that early lets you schedule a wear part replacement during a planned outage, not an emergency shutdown that costs your plant $50,000 an hour in lost generation.
Sand Pump As a FGD pump supplier, I’ve seen every mistake in the book, and I’m here to help you skip them. Whether you need help diagnosing an issue on-site, sourcing genuine replacement parts, or upgrading your pump system with VFDs or better wear components, my team works with power plants of all sizes to keep FGD pumps running strong. If you’re dealing with a persistent issue that’s costing you time and money, don’t hesitate to reach out to our team to schedule a consultation. We’ll come to your site, run a full diagnostic, and give you a clear plan to fix it.
References
- Electric Power Research Institute (EPRI). (2021). FGD Pump Operation and Maintenance Best Practices. EPRI Technical Report.
- Hydraulic Institute. (2019). Pump Guidelines for Slurry and Abrasive Fluids. Hydraulic Institute Standards.
- National Association of Power Utilities (NAPU). (2022). FGD System Reliability Benchmark Report. NAPU Industry Publication.
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