Rod Pump Types: Insert vs. Tubing Pumps and the API Pump Designation
Short answer: rod pumps come in two families. A tubing pump has its barrel built into the tubing string, so it is big but needs the tubing pulled to service it. An insert pump runs in and out on the rods, so it is smaller but comes out with the rods alone. Within each family, an API pump is defined by its barrel wall, where it is held down (top or bottom), whether the barrel or the plunger moves, and the type of seating assembly. All of that is written into the pump's API designation, such as 25-125-RHAC-16-4. 13
How a rod pump works stroke by stroke (barrel, plunger, travelling and standing valves) is covered in the sucker rod pump guide. This guide is about choosing and reading the pump itself.
Tubing pumps vs. insert pumps
The difference is what comes out of the well with the rods. In a tubing pump, the barrel is a joint of the tubing string and only the plunger runs on the rods. In an insert pump, the complete pump runs inside the tubing on the rods and latches into a seating nipple. 12
- Tubing pump (T). Because the barrel is part of the tubing, it can be nearly as wide as the tubing bore, so a tubing pump has the largest displacement of any rod pump for the same tubing size. 3 The cost comes at service time: the barrel can only be serviced by pulling the tubing string. 13
- Insert pump (R, for "rod pump"). The barrel sits inside the tubing, so the plunger is smaller and capacity is lower. In return, service costs less: the whole pump comes out by pulling only the rod string. 3
On a low-rate well, where the cost of each pull matters more than the last barrel of displacement, that difference often decides the choice.
Barrel wall: heavy (H) or thin (W)
The second letter of the designation is the barrel. H is a heavy-wall barrel, W a thin-wall barrel; H, W and X are the most commonly used barrel codes. 1 Wall thickness matters most where the pressure difference across the barrel is high, which is why thin-wall barrels are not recommended for deep wells in the configurations below. 13
Where the pump is held down: top (A) or bottom (B)
The third letter says where the seating assembly sits: A for the top of the pump, B for the bottom. It's the main trade-off in insert pumps, between sand and depth. 13
- Top hold-down (A). The pump seals just below its discharge, so solids have less chance to settle around the barrel and stick the pump in the tubing, and no stagnant fluid sits around the barrel to corrode it. 1 Sand is washed away from the seating nipple as fluid is pumped. 3 The limit is depth: the pressure inside the barrel can far exceed the pressure outside it, which can burst the barrel in deep wells and in wells that are pumped off. The recommendation is shallow to medium depths, with automation to mitigate fluid pound. 1
- Bottom hold-down (B). With the pump above the seating nipple, pressure inside and outside the barrel is about equal, so these pumps suit wells of any depth and are far less likely to burst. 1 The drawback is solids: sand can settle between the barrel and the tubing and stick the pump, though brushes or rubber seals at the top of the pump help. 13 The barrel is also exposed to corrosive well fluid, and the tubing above the seating nipple can erode. 1
Stationary or travelling barrel (T)
In most pumps the barrel stays still and the plunger strokes. In a travelling-barrel pump (third letter T), the plunger stays still on a pull tube and the barrel moves around it. 1
The moving barrel keeps sand and trash in suspension, which is why it is recommended for sandy wells and for wells pumped intermittently. 1 But the design increases the pump's unswept volume, which lowers its compression ratio. That makes it a poor choice for gassy wells (more gas interference), wells with low fluid levels (more fluid pound) and, with a thin-wall barrel, deep wells. 13
Cup or mechanical seating (C or M)
The fourth letter is the seating assembly that holds the pump in the seating nipple: C for cup type, M for mechanical. 1
The cup type is the most versatile: a set of seating cups on a mandrel seals against the seating nipple, and a no-go shoulder stops the assembly from passing through. Cups come in materials from hard plastic, the most common, to high-temperature and composite grades. The mechanical type seals with a metal ring and is used specifically for high downhole temperatures. 1
How to read an API pump designation
An API pump designation, defined in API Specification 11AX, has seven fields separated by dashes: tubing size, pump bore, a four-letter type code, barrel length, plunger length, and the upper and lower extension lengths. 134
Here are two designations read field by field:
| Field | 25-125-RHAC-16-4 | 25-150-RHBC-24-5-2-2 |
|---|---|---|
| Tubing size code | 25 = 2-7/8" tubing 1 | 25 = 2-7/8" tubing 1 |
| Pump bore code | 125 = 1.25" bore | 150 = 1.50" bore 1 |
| 1st letter: pump type | R = rod (insert) pump | R = rod (insert) pump |
| 2nd letter: barrel | H = heavy wall | H = heavy wall |
| 3rd letter: hold-down location | A = top | B = bottom |
| 4th letter: seating assembly | C = cup | C = cup |
| Barrel length | 16 ft | 24 ft |
| Plunger length | 4 ft | 5 ft |
| Upper / lower extension | not given | 2 ft / 2 ft |
So 25-125-RHAC-16-4 is a 1-1/4" insert pump with a heavy-wall barrel and a top cup hold-down, for 2-7/8" tubing, with a 16-foot barrel and a 4-foot plunger. The second example is the one worked through in 1: a 1.50" insert pump with a heavy-wall barrel and bottom cup hold-down in 2-7/8" tubing, 24-foot barrel, 5-foot plunger, 2-foot extensions top and bottom. 1 Extensions apply to heavy-wall barrels. 3
The tubing code is a key, not a measurement: 20 means 2-3/8" tubing and 25 means 2-7/8". 13 The bore code reads in hundredths of an inch: 150 is a 1.50" bore, 1 so 125 is 1.25".
The six common API pumps
Six API pump types cover most wells. Each pairs a pump family with a barrel, a hold-down location and a cup seating assembly. 1
| Pump | What it is | Fits | Avoid |
|---|---|---|---|
| RWAC / RHAC | Insert, thin or heavy wall, top cup hold-down | Sandier wells: stops sand building up around the barrel 1 | Deep wells 1 |
| RWBC / RHBC | Insert, thin or heavy wall, bottom cup hold-down | Wells of any depth: equal pressure inside and outside the barrel 1 | Corrosive fluid without upgraded metallurgy; heavy solids 1 |
| RWTC | Insert, thin wall, travelling barrel, bottom cup hold-down | Sandy wells and intermittent pumping 1 | Gassy wells, low fluid levels, deep wells 1 |
| THBC | Tubing pump, heavy wall, bottom cup hold-down | High fluid production in shallow to medium wells 1 | Gassy wells; costlier to service, because the tubing must be pulled 1 |
Which rod pump type fits which well
Match the pump to the well's biggest problem first, then size it.
- Sand and solids. A top hold-down (RHAC, RWAC) keeps sand from packing around the barrel; a travelling barrel (RWTC) keeps solids moving. 12 SPE's rod-lift webinar also lists chrome barrels and spray-metal plungers for sandy wells. 2
- Depth. A bottom hold-down (RHBC, RWBC) with a heavy-wall barrel, because pressure across the barrel stays balanced. 1
- Gas. Avoid the travelling barrel and the tubing pump, which both leave more room for gas to expand. 1 For gassy wells, SPE's webinar suggests longer-stroke, smaller-diameter pumps, RW or RX pumps without extensions, or an RH pump with a zero extension on the bottom, and reducing the pump's unswept volume. 2 Separating gas before it reaches the pump matters as much: see gas-locked rod pump.
- Heavy oil. Large-diameter insert pumps and oversized tubing pumps with generous clearances. 2 See heavy oil rod pumping.
- Volume. A tubing pump moves the most fluid for a given tubing size, if the well is shallow to medium depth and not gassy. 13
- Pulling cost. An insert pump comes out with the rods; a tubing pump takes a tubing job. 3 On wells where every pull hurts, see workover cost and stripper well economics.
Plunger length follows depth. A common rule of thumb: a 3-foot plunger for pumps set shallower than 3,000 feet; one foot of plunger per 1,000 feet of depth between 3,000 and 6,000 feet; and 6 feet below 6,000 feet, unless conditions call for something else. 1
Whatever the pump, it still sits at the bottom of a rod string that can buckle on the downstroke. Choosing the right pump type doesn't remove that.
Where SRABS fits
SRABS works on the rod-pumped well from the pump up. In the words of the how it works page: "The SRABS Pump is a drop-in anti-buckling rod pump: it solves buckling at the source instead of adding weight to fight it." See the system for the full stack.
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
Most of the decision is in four letters. The pump family sets displacement against pulling cost, the hold-down sets sand against depth, and a travelling barrel trades sand handling for gas trouble. Read the designation, match it to the well's main problem, and the rest is sizing.
See what a better pump does on a real well.
FAQ
What is the difference between an insert pump and a tubing pump?
In a tubing pump the barrel is a joint of the tubing string, so it has the largest displacement for its tubing size, but servicing it means pulling the tubing. An insert pump runs complete inside the tubing on the rods, so it is smaller but comes out by pulling only the rods.
What does RHAC mean on a rod pump?
R means a rod, or insert, pump; H a heavy-wall barrel; A a hold-down at the top of the pump; and C a cup-type seating assembly. An RHAC pump suits sandier wells, because the top hold-down stops sand building up around the barrel, but it is not recommended for deep wells.
How do you read an API pump designation?
Read the seven dash-separated fields in order: tubing size code, pump bore, the four-letter type code, barrel length in feet, plunger length in feet, then upper and lower extensions. For example, 25-125-RHAC-16-4 is a 1-1/4" heavy-wall insert pump with a top cup hold-down for 2-7/8" tubing, with a 16-foot barrel and 4-foot plunger.
Which rod pump is best for sandy wells?
A top hold-down insert pump such as an RHAC or RWAC, which keeps sand from settling around the barrel, or a travelling-barrel RWTC, which keeps solids in suspension. Chrome barrels and spray-metal plungers help with wear. Avoid the RWTC if the well is also gassy or has a low fluid level.
Which rod pump should I use in a deep well?
A bottom hold-down insert pump with a heavy-wall barrel, such as an RHBC. With the seating assembly at the bottom, pressure inside and outside the barrel is about equal, so the barrel is far less likely to burst. Top hold-down and thin-wall travelling-barrel pumps are not recommended for deep wells.
Sources
- 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
- Chokshi, R., Lane, B., "Reciprocating Rod Lift (RRL)," SPE Artificial Lift webinar series, webinar 2, September 23, 2014. https://file.streaming.spe.org/wp-content/uploads/2024/02/22131640/Reciprocating-Rod-Lift-RRL-.pdf
- Fetoui, I., "API Subsurface Pump Designation," Production Technology, July 3, 2018. https://production-technology.org/api-subsurface-pump-designation/
- American Petroleum Institute, API Specification 11AX, "Specification for Subsurface Sucker Rod Pumps and Fittings."