API Pump Designation: How to Read a Rod Pump Code, Letter by Letter
Short answer: an API pump designation is the code stamped on a sucker rod pump, such as 25-175-RHBC-20-4-2-2. Read left to right, it gives the tubing size, the pump bore, four letters for the pump type, barrel, seating location and seating assembly, then the barrel length, plunger length and the upper and lower extensions. The format comes from API Specification 11AX. 138
For choosing between pump types, see rod pump types; for how the pump strokes, see the sucker rod pump guide.
What is an API pump designation?
An API pump designation is a short code, defined in API Specification 11AX, that describes a subsurface sucker rod pump completely enough to order or identify it. It has seven sections: tubing size, pump bore, a four-letter type code, barrel length, plunger length, and the lengths of the upper and lower extensions. 238
API 11AX standardizes pump dimensions, labeling and quality control, but not which pump suits which well. 2 The designation tells you what a pump is, not whether it fits.
The standard's own example, from its 2019 addendum, is: 1
20-125 RHBC 10–04–2.0–2.0
That is a 1-1/4" bore rod-type pump with a 10-ft heavy-wall barrel, 24-in. upper and lower extensions, a 4-ft plunger and a bottom cup-type seating assembly, for 2-3/8" tubing. 1
The seven fields, decoded
Read the designation in seven sections from left to right: a two-digit tubing code, a three-digit bore code, four letters, then barrel length, plunger length, upper extension and lower extension. The numbers before the letters are size keys; the numbers after them are lengths in feet. 123
| # | Field | Format | What it means |
|---|---|---|---|
| 1 | Tubing size | 2 digits, e.g. 25 | Code for the nominal tubing OD the pump runs in, not a measurement 34 |
| 2 | Pump bore | 3 digits, e.g. 175 | Basic bore of the pump 3 |
| 3 | Pump type | 1 letter: R or T | Rod (insert) pump or tubing pump 23 |
| 4 | Barrel type | 1 letter: H, W, P, S or X | Wall thickness and plunger type 3 |
| 5 | Seating location | 1 letter: A, B or T | Top, bottom, or bottom with a traveling barrel 3 |
| 6 | Seating assembly | 1 letter: C or M | Cup or mechanical 3 |
| 7 | Barrel length | feet | 2 to 40 ft in 1-ft steps 1 |
| 8 | Plunger length | feet | Nominal length, 2 ft and longer in 1-ft steps 1 |
| 9 | Upper extension | decimal feet | 0.3 to 4.0 ft (3 to 48 in.) 1 |
| 10 | Lower extension | decimal feet | 0.3 to 4.0 ft (3 to 48 in.) 1 |
The four letters count as one section. 2 Older catalogues give the extensions in whole feet, so you will see both 10-4-2-2 and 10–04–2.0–2.0 for the same pump. The 2019 addendum changed the extension fields to decimal feet, and one of its pump tables gives 24 and 36 in. (2.0 and 3.0 ft) as the standard extension lengths. 13 If a designation stops after the plunger length, as in 25-125-RHAC-16-4, no extensions are specified.
Tubing size and pump bore codes
The first number is a key for the tubing the pump runs in: 15, 20, 25, 30 and 40 stand for 1.900", 2-3/8", 2-7/8", 3-1/2" and 4-1/2" OD tubing. The second number is the bore in hundredths of an inch, so 125 is 1-1/4" and 175 is 1-3/4". 3
The values below are from a pump supplier's catalogue that reproduces API Spec 11AX Table B.1 and Figure B.1. 3
| Tubing code | Tubing OD |
|---|---|
| 15 | 1.900 in. (48.3 mm) |
| 20 | 2-3/8 in. (60.3 mm) |
| 25 | 2-7/8 in. (73.0 mm) |
| 30 | 3-1/2 in. (88.9 mm) |
| 40 | 4-1/2 in. (114.3 mm) |
| Bore code | Basic bore |
|---|---|
| 125 | 1-1/4 in. (31.8 mm) |
| 150 | 1-1/2 in. (38.1 mm) |
| 175 | 1-3/4 in. (44.5 mm) |
| 178 | 1-25/32 in. (45.2 mm) |
| 200 | 2 in. (50.8 mm) |
| 225 | 2-1/4 in. (57.2 mm) |
| 250 | 2-1/2 in. (63.5 mm) |
| 275 | 2-3/4 in. (69.9 mm) |
| 375 | 3-3/4 in. (95.3 mm) |
The tubing code is a key, not a dimension: 2-7/8" tubing is coded 25, not 28. 34
The four letters
The four letters say, in order: what kind of pump it is (R or T), what barrel it has (H, W, P, S or X), where it is held down (A, B or T), and how it is held down (C or M). RHBC, for example, is a rod pump with a heavy-wall barrel and a bottom cup seating assembly. 23
| Position | Letter | Meaning |
|---|---|---|
| 1st: pump type | R | Rod pump, also called an insert pump: runs inside the tubing on the rods 34 |
| T | Tubing pump: the barrel is part of the tubing string 34 | |
| 2nd: barrel | H | Heavy wall, for metal plunger pumps 3 |
| W | Thin wall, for metal plunger pumps 3 | |
| P | Heavy wall, for soft-packed plunger pumps 3 | |
| S | Thin wall, for soft-packed plunger pumps 3 | |
| X | Heavy wall for metal plunger pumps, with a thin-wall thread configuration 3 | |
| 3rd: seating location | A | Top, stationary barrel 34 |
| B | Bottom, stationary barrel 34 | |
| T | Bottom, traveling barrel 34 | |
| 4th: seating assembly | C | Cup type 3 |
| M | Mechanical (metal seat) 34 |
Two letters do double duty, so read them by position. T in first place means tubing pump; T in third place means traveling barrel. RWTC is therefore a rod pump with a thin-wall barrel, a traveling barrel and a cup seating assembly, not a tubing pump. 23
H, W and X are the barrel codes you will meet most often. 2 P and S are the soft-packed-plunger versions of the heavy-wall and thin-wall barrels. 3
Every combination API 11AX defines
API 11AX does not allow every letter combination. Its table lists rod pumps with top or bottom anchors and stationary or traveling barrels, an X barrel only with a stationary bottom anchor, and tubing pumps in heavy-wall metal (TH) and heavy-wall soft-packed (TP) versions. 3
| Pump | Heavy wall, metal plunger | Thin wall, metal plunger | Heavy wall, soft-packed | Thin wall, soft-packed |
|---|---|---|---|---|
| Rod pump, stationary barrel, top anchor | RHA | RWA | — | RSA |
| Rod pump, stationary barrel, bottom anchor | RHB | RWB | — | RSB |
| Rod pump, stationary barrel, bottom anchor (X barrel) | RXB | — | — | — |
| Rod pump, traveling barrel, bottom anchor | RHT | RWT | — | RST |
| Tubing pump | TH | — | TP | — |
A dash means the combination isn't defined. Add C or M for the seating assembly: RHA becomes RHAC or RHAM. 3
Tubing pump codes. The table lists tubing pumps without a seating-location letter. 3 In a tubing pump the standing valve seats in a seating nipple, and the last letter gives its type: the same catalogue lists THC (with a cup-type seating nipple) and THM (with a mechanical lock seating nipple). 3 You will also see the longer form THBC in print, read as tubing, heavy wall, bottom, cup. 2
Common pump types and when each is used
Six API pumps cover most wells: RHAC and RWAC for sand, RHBC and RWBC for depth, RWTC for sand and intermittent pumping, and the tubing pump for volume. The less common codes, RXBC, RHBM and THM, answer a specific condition: depth without extensions, high temperature, or a tubing pump with a metal seat. 234
| Code | Reads as | Typically used | Watch out for |
|---|---|---|---|
| RHAC / RWAC | Rod pump, heavy or thin wall, top, cup | Sandier wells: sand can't pack around the barrel 24 | Deep wells, especially with a thin-wall barrel 24 |
| RHBC / RWBC | Rod pump, heavy or thin wall, bottom, cup | Wells of any depth: pressure inside and outside the barrel is about equal 2 | Corrosion of the exposed barrel; solids settling around it 24 |
| RHBM | Rod pump, heavy wall, bottom, mechanical | High downhole temperatures, where plastic cups deteriorate 2 | Needs a mechanical seating nipple 2 |
| RXBC | Rod pump, X barrel, bottom, cup | Deeper settings: the X barrel needs no extensions 4 | Only defined with a stationary bottom anchor 3 |
| RWTC | Rod pump, thin wall, traveling barrel, cup | Sandy wells and intermittent pumping: the moving barrel keeps solids in suspension 24 | Gassy wells, low fluid levels, deep wells, viscous fluid 24 |
| THBC / THC / THM | Tubing pump, heavy wall, cup or mechanical seating | High fluid volume in shallow to medium wells; viscous fluid 24 | Gassy wells; the tubing must be pulled to service the barrel 24 |
The reasons behind these trade-offs are in rod pump types and gas-locked rod pump.
Cup or mechanical. Cup seating assemblies seal with seating cups on a mandrel and are the most versatile option; mechanical ones seal with a metal ring for high temperatures. 2 Cups are economical but normally can't be re-seated after a workover; a mechanical seat costs more but can be used several times. 4
Worked examples
To decode a designation, split it at the dashes, look up the two size codes, read the four letters by position, and treat the remaining numbers as lengths in feet: barrel, plunger, then the upper and lower extensions. The three examples below cover an insert pump with extensions, the standard's own example and a tubing pump. 123
25-175-RHBC-20-4-2-2
| Field | Value | Meaning |
|---|---|---|
| 25 | Tubing | 2-7/8" OD tubing 3 |
| 175 | Bore | 1-3/4" 3 |
| R H B C | Type | Rod (insert) pump, heavy-wall barrel, bottom stationary anchor, cup seating 3 |
| 20 | Barrel | 20 ft |
| 4 | Plunger | 4 ft |
| 2 / 2 | Extensions | 2 ft upper, 2 ft lower |
Barrel plus extensions is 20 + 2 + 2 = 24 ft. In pump sizing, that total is set from the downhole stroke length plus the plunger length. 2
20-125 RHBC 10–04–2.0–2.0. The standard's own example: a 1-1/4" bore rod pump with a 10-ft heavy-wall barrel, 24-in. extensions top and bottom, a 4-ft plunger and a bottom cup seating assembly, for 2-3/8" tubing. 1 Note the decimal-feet extensions.
25-225 THM. A tubing pump for 2-7/8" tubing with a 2-1/4" bore and a heavy-wall barrel, whose standing valve locks into a mechanical seating nipple. 3 Lengths are added when ordering. Compare 25-225 with the 25-175 insert pump above: same tubing, bigger bore. That is why a tubing pump has the largest displacement of any rod pump for a given tubing size. 4
The downhole parts the code names
The designation names the main parts of the pump: the barrel (wall type and length), the plunger (length and type), the seating assembly that holds the pump in the seating nipple, and the extensions. The standing and traveling valves are implied: every pump has both, and the code's pump type says where they sit. 23
- Barrel. The cylinder the plunger strokes in. Its wall (H, W, P, S or X) and length are in the code. 3 In a tubing pump the barrel is a joint of the tubing string; in an insert pump it runs inside the tubing. 24
- Plunger. The close-fitting piston. Lengths commonly range from 3 to 6 ft, with longer plungers run in some wells. 2 The barrel letter also says whether the plunger is metal (H, W, X) or soft-packed (P, S). 3
- Traveling valve. The check valve in the plunger that closes the barrel chamber so the trapped fluid is lifted on the upstroke. 6
- Standing valve. The check valve at the bottom of the pump that lets fluid flow up to fill the barrel and stops it from flowing back down. 5 Both valves are ball-and-seat valves held in cages. 2
- Seating assembly (hold-down). The cup or mechanical assembly that locks the pump into the seating nipple, at the top (A) or bottom (B, T) of an insert pump. 23
- Seating nipple. In completion terms, a short section of heavy-wall tubular with a machined internal surface that provides a seal area and a locking profile. 7 A mechanical seating assembly needs a mechanical seating nipple. 2
- Extensions. Short barrel extensions (extension nipples or couplings) above and below a heavy-wall barrel, given as the last two numbers of the code. 134 The X barrel does not need them. 4
What moves the plunger or the barrel? The rod string. In a stationary-barrel insert pump, the bottom rod connects to a valve rod, which runs through a valve-rod guide on the barrel assembly and drives the plunger. 3 In a tubing pump, the plunger assembly runs directly on the rod string. 2 In a traveling-barrel pump (third letter T) it is the other way round: the plunger stays still at the bottom anchor and the rods move the barrel around it. 23
Whatever the code, the pump hangs from a rod string stroked by the pumping unit, and that string can buckle.
Where SRABS fits
The SRABS Pump is built to fit the same API-spec completion as a standard rod pump. In the words of the how it works page, it "is a drop-in anti-buckling rod pump: it solves buckling at the source instead of adding weight to fight it." The system lists its retrofit as "Drop-in · API spec."
To estimate what fewer failures would mean for your fleet, run the ROI calculator. Its default 100-well scenario is modelled, not a field result.
The bottom line
The code is a complete description, not a recommendation. Two size keys, four letters and up to four lengths tell you exactly what is in the hole. Read the letters by position, check the tubing and bore codes, and then judge the pump against the well: sand, depth, gas and temperature.
If the same wells keep failing whatever pump you run, test the fix on one well.
FAQ
How do you read an API pump designation?
Split it at the dashes. The first number is the tubing code (25 = 2-7/8" tubing), the second the bore (175 = 1-3/4"), then four letters for pump type, barrel, seating location and seating assembly, then barrel length, plunger length and the upper and lower extensions, all in feet.
What does RHBC mean on a rod pump?
R is a rod, or insert, pump; H a heavy-wall barrel for a metal plunger; B a stationary barrel held down at the bottom; and C a cup-type seating assembly. With the pump held down at the bottom, pressure inside and outside the barrel is about equal, so RHBC pumps suit wells of any depth.
What does the T mean in RWTC and in THM?
It depends on its position. In first place, T means a tubing pump, as in THM: tubing pump, heavy wall, mechanical seating. In third place, T means a traveling barrel, as in RWTC: an insert pump whose barrel moves while the plunger stays still at the bottom anchor.
What are the downhole components of a sucker rod pump?
A barrel, a plunger, a traveling valve in the plunger, a standing valve at the bottom of the pump, and a seating assembly that locks the pump into a seating nipple in the tubing. Heavy-wall barrels also carry upper and lower extensions.
What moves the plunger in a rod pump?
The rod string. In a stationary-barrel insert pump, the bottom rod connects to a valve rod that drives the plunger. In a tubing pump, the plunger runs directly on the rods. In a traveling-barrel pump, the plunger stays still and the rods move the barrel.
Sources
- American Petroleum Institute, API Specification 11AX, 13th Edition, Addendum 1 (May 2019), designation example and length fields. https://www.api.org/-/media/Files/Certification/Monogram-APIQR/0_API-Monogram-APIQR/Advisories-Updates/Addenda-Errata/API%2011AX%2013th%20Edition%20Addendum%201%2020190513.pdf
- Monk, A., Thompson, L., Smith, Z., Roderick, R., "Sucker-Rod Pump Selection and Application," Southwestern Petroleum Short Course, 2018. https://www.swpshortcourse.org/sites/default/files/papers/2018018.pdf
- DNOW, Dura Products Catalogue 2021, "API Pump Designation" (reproducing API Spec 11AX 13th Edition Table B.1 and Figure B.1) and tubing pump pages. https://www.dnow.com/hubfs/WC/PDF/Products/Artificial-Lift/Dura_Products_Catalogue_2021.pdf
- Fetoui, I., "API Subsurface Pump Designation," Production Technology, July 3, 2018. https://production-technology.org/api-subsurface-pump-designation/
- SLB Energy Glossary, "standing valve." https://glossary.slb.com/en/terms/s/standing_valve
- SLB Energy Glossary, "traveling valve." https://glossary.slb.com/en/terms/t/traveling_valve
- SLB Energy Glossary, "seating nipple." https://glossary.slb.com/en/terms/s/seating_nipple
- American Petroleum Institute, API Specification 11AX, "Specification for Subsurface Sucker Rod Pump Assemblies, Components, and Fittings."