Your beam pump is pumping units, the well isn't flowing, and something's wrong. Could be a rod, could be the downhole pump, could be gas. The job is figuring out which one — fast — before you spend half a day pulling a string that doesn't need to be pulled.
Rod pumping systems fail in predictable ways. The five failure modes covered here account for the overwhelming majority of rod pump service calls. Learn the symptoms, learn the checks, and you'll diagnose most problems at the wellhead without a fishing job.
Read the Dynacard First
If you have a pump-off controller or a downhole dynamometer, pull the dynacard before you do anything else. A dynamometer card is a plot of polished rod load vs. position — the shape of that card tells you what's happening 3,000 feet down the hole better than any surface symptom. A full, square card means the pump is working. A narrow card means it's not filling. A card with a floor means gas. A card with no lower turn means a parted rod.
If you don't have dynacard capability on location, surface readings — polished rod load, stroke length, SPM, and production — are your next best tool. Take baseline readings when the well is running right; deviation from baseline is your diagnostic signal.
Failure Mode 1: Rod Parting
A parted rod is the most dramatic failure. The string breaks somewhere in the well and the bottom half — rods, downhole pump, everything below the break — drops to bottom. Production stops immediately.
What You'll See at the Surface
- Polished rod load drops sharply — the counterbalance is now much heavier than the rod load, which is carrying only a partial string
- The unit sounds different — lighter, faster, the counterbalance is leading instead of trailing
- No fluid production
- Sometimes the beam will hit its travel stops if the controller doesn't shut it down first
Common Causes
- Fatigue failure: Rods run at excessive load or with inadequate fall-back on the down stroke accumulate fatigue cycles at couplings and tapers. The weak point eventually cracks and parts. This is the most common rod parting cause in high-GOR or deviated wells.
- Corrosion: H₂S, CO₂, and produced water accelerate rod corrosion — especially at coupling shoulders and pin threads. Pitting from corrosion becomes a stress riser. Fiberglass rods and corrosion-resistant couplings exist for a reason.
- Improper makeup torque: Under-torqued couplings back off in service. Over-torqued ones yield at the pin. Either way the coupling is the failure point.
- Running in deviated wellbore without centralizers: Rod wear in a crooked hole concentrates side loading at contact points. Given enough cycles, those points fatigue and part.
What to Do
Confirm the part with a surface dynacard or by measuring the polished rod load with a load cell. Once confirmed, you're pulling the string. Document the part depth — rod count on the way out tells you which rod parted and gives you data for the next string design. If you find corrosion pitting, test your produced water chemistry before you run the replacement string.
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Subscribe Free →Failure Mode 2: Fluid Pound
Fluid pound happens when the downhole pump doesn't fill completely on the upstroke. On the downstroke, the plunger slams into fluid instead of compressing a full column — you get a hammering impact that runs all the way up the rod string and into the surface unit.
What You'll See
- Audible bang or clunk at the bottom of each stroke — you can feel it on the beam and hear it if the well isn't too deep
- Dynacard shows a sharp load spike on the downstroke where the plunger hits fluid
- Surface card looks like the bottom corner of the card is "cut off" instead of a smooth lower turn
- Accelerated rod and pump wear — fluid pound puts enormous shock load on the string every cycle
Common Causes
- Pump set too high: The pump intake is above the fluid level in the casing annulus. You're pumping air or gas instead of fluid on part of every stroke.
- Well is pumped off: The well's inflow rate can't keep up with pump displacement. This is the normal condition for a pump-off controller — it should be shutting the unit down. If the POC isn't working, the unit runs in fluid pound continuously.
- High GOR without gas anchor: Gas breaks out of solution downhole and enters the pump intake. The pump compresses gas instead of lifting fluid. Classic gas interference.
- Worn standing valve: The standing valve (bottom check) is leaking. Fluid falls back through it on the downstroke, so the pump never fills completely.
What to Do
Check your pump-off controller first — if it's malfunctioning, fixing it might solve the problem without a service call. If the well is genuinely pumped off, reduce strokes per minute or install a timer. If you suspect a leaking standing valve, a surface fillage test (count strokes to fill a tank increment) and a valve test on pull will confirm it. If it's gas interference, the fix is a gas anchor — a dip tube that separates free gas from the fluid before it enters the pump intake.
Failure Mode 3: Gas Interference
Gas interference is related to fluid pound but distinct enough to cover separately. When high-GOR fluid enters the pump, free gas compresses on the downstroke instead of lifting fluid. Efficiency drops. Production falls. The pump may lock — a "gas lock" — where the gas compresses and expands without ever opening either valve. No fluid is moved. The unit keeps stroking. The well appears to be pumping.
Symptoms
- Low production relative to expected fluid level and pump displacement
- Erratic production — high on one day, low on the next, tracking with casing pressure fluctuations
- Dynacard shows a compressed, "gas card" shape — narrow bottom, load doesn't drop cleanly on the down stroke
- Casing pressure builds up between pump cycles if the annulus isn't vented
Fixes
- Gas anchor: The standard fix. A dip tube set below the pump intake draws fluid from the bottom of the annulus, separating free gas upward before it enters the pump. Simple, effective, cheap.
- Vent the casing: If the annulus is pressured up, vent it to the sales line or a low-pressure separator. High casing pressure forces gas into the pump intake.
- Reduce stroke rate: Slower strokes give more time for gas to separate from the fluid before pump intake. Sometimes reducing SPM by 20% eliminates the gas interference problem.
- Increase pump submergence: Set the pump deeper so it's farther below the fluid level. More hydrostatic head at the intake helps compress the gas before it enters the pump barrel.
Failure Mode 4: Stuffing Box Leaks
The stuffing box seals the polished rod at the surface. When it leaks, you get produced fluid — sometimes crude, sometimes produced water, sometimes both — coming out around the polished rod. It's a mess, it's a spill risk, and in some jurisdictions it's a regulatory violation.
Types of Leaks and What Causes Them
| Symptom | Likely Cause | Fix |
|---|---|---|
| Slow seep around polished rod, gets worse over time | Packing worn — normal wear cycle | Tighten gland nut first; if still leaking, replace packing |
| Sudden heavy leak after rod work | Packing not seated properly after last service; rod not centered | Check rod alignment, re-seat packing, confirm rod is straight |
| Leak that tightening makes worse (gland bottoms out) | Packing is completely spent — no material left to compress | Replace packing — do not continue tightening |
| Leak at bottom of stuffing box (below packing area) | Body seal or flange gasket failed | Replace body seal; check flange faces for damage |
| Polished rod wear visible (flat spot, groove) | Rod not centered; excessive side load; misalignment | Check alignment of wellhead, beam, and rod; replace polished rod |
Packing Selection
Packing choice matters. Braided packing is cheap and fine for low-pressure sweet service. For H₂S or CO₂ environments, use HNBR or Viton packing — they hold up in corrosive service. For hot produced water, check the temperature rating. Running the wrong packing chemistry in a sour well means replacing it every month instead of every six.
Failure Mode 5: Polished Rod Wear
The polished rod runs through the stuffing box on every stroke. A rod that's worn — flat spots, corrosion pits, scoring from a tight stuffing box — destroys packing fast and eventually becomes a leak factory regardless of how often you replace the seals.
How to Inspect It
- Run your hand along the rod at the stuffing box zone. Any rough spots, pitting, or flat areas? That's your culprit.
- Check for straightness. Set the rod in V-blocks or roll it on a flat surface. Bend greater than 0.030" per foot is enough to cause eccentric wear in the stuffing box.
- Look at the packing wear pattern. Uniform wear = centered rod. One-sided wear = side load or misalignment.
- Check the lower coupling. A worn or loose lower coupling lets the rod move laterally and accelerates polished rod wear.
When to Replace
A polished rod with surface pitting, flat spots, or scoring more than 0.010" deep should be replaced — not polished down and returned to service. The damaged area is a stress riser, and in service it keeps destroying packing. The rod is relatively cheap. The fishing job you'll do when it eventually parts is not.
Quick Diagnostic Reference
| What You Observe | Most Likely Cause | First Check |
|---|---|---|
| Production dropped to zero, unit sounds light | Parted rod | Polished rod load vs. baseline; dynacard |
| Bang or thud at bottom of every stroke | Fluid pound | POC function; fluid level; standing valve condition |
| Low production, casing pressure building | Gas interference | Vent casing annulus; check gas anchor; reduce SPM |
| Fluid weeping around polished rod | Stuffing box packing worn or spent | Tighten gland; inspect packing age; check rod surface condition |
| Packing replaced repeatedly, still leaking | Worn or bent polished rod; misalignment | Inspect rod surface; check rod straightness; check beam/wellhead alignment |
| Production declining over weeks, dynacard normal | Pump barrel/plunger wear or sand fill | Pump fillage test; check for sand production; consider pulling pump |
On-Location Checklist Before You Pull
Before you call for a service truck and commit to a pull, run through this list. You can do all of these at the wellhead in under 30 minutes.
- Record polished rod load (max and min) and compare to baseline. A big deviation tells you something changed structurally in the well.
- Check pump-off controller settings and confirm it's actually functioning. A failed POC running fluid pound looks like a downhole pump problem from the surface.
- Measure strokes per minute. Verify the unit is running at the set point — a slipping belt or brake issue can change SPM without anyone noticing.
- Pull a dynacard if equipment is available. Even a surface card gives you structural information about what's happening downhole.
- Check the stuffing box — tighten the gland if leaking; inspect the polished rod for wear at the packing zone.
- Read casing pressure. High casing pressure means gas accumulation in the annulus — vent it and see if production improves before doing anything else.
- Verify the wellhead is aligned with the beam centerline. Side loading from misalignment accelerates every failure mode.
- Check counterbalance. If the counterbalance is misadjusted, the rod string is either overloaded on the upstroke or undersupported on the down stroke — both accelerate fatigue.
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Get the Newsletter →Preventing the Next Failure
Most rod pump failures are predictable. The equipment tells you what's coming — you just have to be collecting the data. Three things prevent most rod pump field calls:
- Baseline everything. Document polished rod load, SPM, production rate, and fluid level when the well is running correctly. Every service call starts with "what changed" — and you can only answer that if you have a baseline to compare against.
- Set the pump-off controller correctly and verify it's working. A properly calibrated POC prevents fluid pound, which is the leading cause of accelerated wear in rod pump systems. Check the POC monthly — they fail quietly and nobody notices until you're replacing a rod string.
- Design the string for the well, not the warehouse. The right rod taper, the right material grade, the right pump size for the fluid level and production rate. An undersized pump run at maximum SPM fails faster than a properly sized pump run at 60%. If the well's conditions have changed significantly since the last string design, it's worth a recalculation before the next pull.