How to Read Basic Dynamometer Card Shapes
A dynamometer card is the single most useful diagnostic a rod-pumped well produces, and most of its value is in the outline, not the numbers. An engineer who can glance at the shape and name the condition - full pump, fluid pound, gas, a leaking valve - can act before the well loses production or breaks rods. This page teaches the handful of canonical shapes you will actually see in the field and what each one means. It is a reading guide, not a controller-setup procedure; use it once your sensors are verified and you are looking at real cards on the trend.
Interpret Dyno Card Shape in one line: To read a dynamometer card shape, look at where load is picked up and dropped around the loop. A full pump is a clean parallelogram with a sharp load pickup at the bottom of the upstroke and a sharp drop at the top. A fluid-pound card shows load holding high late into the downstroke then dropping abruptly, meaning the pump did not fill. A gas-interference card rounds off that same corner instead of dropping sharply. A rounded, collapsed loop with low peak load usually means a worn or leaking pump.
Recognize the Full-Pump Reference Shape
Everything you diagnose is measured against a full pump, so learn that shape first. When the pump fills completely with liquid every stroke, the surface card is close to a parallelogram: load rises sharply at the bottom of the stroke as the traveling valve takes the fluid load, stays high and roughly flat across the upstroke, drops sharply at the top as the load transfers back to the standing valve, and stays low across the downstroke. The two sharp corners - pickup at bottom, release at top - are the signature of a pump that is filling and both valves sealing.
The height of the card tells you the fluid load and the width tells you the effective stroke. A full card that is tall carries more fluid; a full card that is short is lifting less. Comparing today's full card against the commissioning card is how you notice a rising or falling fluid level over weeks. This is the same fluid load and fillage the controller uses, and it helps to keep the definition of pump fillage in mind while you read the corners.
One caution: the surface card is distorted by rod dynamics and does not equal the downhole card. Most controllers compute a downhole card from the surface card, and the downhole version shows the pump condition more cleanly. If your system offers both, diagnose from the downhole card and use the surface card mainly to confirm the sensors are behaving, a distinction covered in surface versus downhole dynamometer cards.
Name the Incomplete-Fill and Leak Shapes
Fluid pound is the shape you will see most on a pumped-off well. The pump fills only partway with liquid, so on the downstroke the plunger falls through gas or vapor and then slaps into the liquid surface. On the card, load stays high well past where it should have dropped, then falls off abruptly late in the stroke - a sharp step down on the right side of the loop. That late, hard drop is the mechanical pound that damages rods and pumps, and its position on the card tells you roughly how empty the pump was.
Gas interference produces a similar incomplete-fill card but with a rounded rather than a sharp transition. When free gas compresses and expands in the pump barrel instead of liquid slapping, the load releases gradually and the corner is soft and curved rather than a step. Telling these apart matters because the fixes differ, and the distinction between fluid pound and gas interference is exactly the sharp-versus-rounded corner on the downstroke.
Valve leaks and worn pumps collapse and round the whole loop. A traveling-valve or plunger leak lets load bleed off during the upstroke, so the top of the card sags instead of holding flat. A standing-valve leak lets load rise early on the downstroke. A badly worn pump gives a low, rounded, shrunken loop with soft corners everywhere, because it can no longer build or hold the fluid load. When the card is small and the peak load is well below the expected fluid load, suspect the pump itself rather than the reservoir.
Work Through a Card Systematically
Read every card in the same order so you do not jump to a conclusion. First check that the loop is a plausible closed shape and the load band matches the expected fluid load - if not, suspect the install before the pump. Second, look at the bottom-of-upstroke corner: a sharp pickup means the traveling valve is sealing and taking load. Third, look at the top and the downstroke: a flat, held upstroke top means no traveling-valve leak, and a sharp versus rounded drop separates fluid pound from gas.
Then step back and compare against history. A single card names a condition; a trend of cards tells you whether it is getting worse. A fluid-pound card that appears intermittently on a well that used to pump full is telling you the inflow can no longer keep up with the pump, which is a speed or timing decision for the controller. The same card appearing suddenly and severely may mean a tubing or downhole problem instead. Reading the shape is step one; reading the change over time is what drives the action.
The table below summarizes the four shapes you will identify most often and the corner that gives each one away, so you can pattern-match quickly in the field.
| Card shape | Telltale feature | Likely condition |
|---|---|---|
| Clean parallelogram | Sharp pickup at bottom, sharp drop at top, flat top | Full pump, both valves sealing |
| Load held then sharp late drop | Abrupt step down on the downstroke | Fluid pound, incomplete liquid fill |
| Load held then rounded drop | Soft, curved transition on the downstroke | Gas interference in the barrel |
| Small, rounded, low loop | Sagging top, soft corners, low peak load | Worn pump or leaking valve |
Common Mistakes
The biggest mistake is diagnosing from the surface card when a downhole card is available. Rod stretch and dynamics smear the surface card, and a surface fluid-pound signature can look worse or milder than the real pump condition. If the controller computes a downhole card, read that for pump diagnosis and keep the surface card for install checks.
The second is confusing fluid pound with gas interference because both are incomplete-fill cards. The discriminator is the shape of the downstroke transition: sharp step equals liquid pound, rounded curve equals gas. Acting on the wrong one wastes effort, because you slow the pump or add downhole gas handling for the wrong reason. The third is reading a single card as a verdict rather than watching whether the shape is stable, worsening, or intermittent over the trend.
Frequently Asked Questions
What does a fluid pound card look like?
On a fluid-pound card, load stays high across the upstroke and holds high past the point where it should release, then drops sharply and late on the downstroke. That abrupt, late step down is the plunger falling through gas and slapping into the liquid surface because the pump did not fill completely. The sharpness of the drop separates it from gas interference, which rounds the same corner off instead of stepping down.
How can I tell gas interference from fluid pound on a card?
Look at the downstroke transition. Fluid pound shows a sharp, sudden step down late in the stroke as liquid is struck. Gas interference shows a rounded, gradual load release because compressed gas expands smoothly instead of liquid slapping. Same incomplete-fill situation, different corner shape. Getting this right matters because the two conditions call for different responses from the pump-off controller and the well plan.
Should I diagnose from the surface or downhole card?
Diagnose the pump from the downhole card when your controller computes one, because it removes the rod-string dynamics that distort the surface card. Use the surface card mainly to confirm the load and position sensors are installed and reading correctly. A surface card is enough to spot gross problems, but the downhole card gives the cleanest picture of what the pump and valves are actually doing.
Automation services
Need help turning this into a working system?
Merobix integrates SCADA, programs Allen-Bradley and Siemens PLCs, and designs and fabricates industrial control panels.
Meeting requests are reviewed before confirmation.