A pump shaft bushing, a butterfly valve trunnion and a hydraulic cylinder rod-end bushing each solve the same problem in a different fluid. All three must run where an oil film is unreliable or where the process medium is the only “lubricant”, carry steady load, and survive an environment that may be seawater, a chemical process fluid or hydraulic oil under pressure. This page maps bronze bushing applications in pumps, valves and fluid power, and the alloys and plug materials that fit each service.

1. What pump, valve and cylinder service does to a bearing

The bearings in this industry sit closer to the process fluid than almost any other bearing, and that single fact governs every choice. In a pump, the bushing may be lubricated by the pumped fluid; in a valve it may run dry for long periods and then move under pressure; in a hydraulic cylinder it runs in oil but under very high pressure and frequent reciprocation. Each of these removes the assumption a workshop bushing relies on — that a clean oil film will be maintained.

Three consequences follow. Corrosion becomes a first-order selection factor, because the medium is often seawater, a chemical, or a fluid with entrained solids. The bearing must tolerate boundary or dry running because a hydrodynamic film is rarely present. And in a valve the bearing is inside a pressure-retaining component, so its wear and seizure behaviour affects sealing and, in some services, safety. Selecting bronze for these duties is as much about matching the fluid as matching the load.

2. Bushing applications by component

Application mapping is based on common layouts and is for orientation; the equipment drawing and code take precedence for any specific machine.

3. Process media decide the material

In most industries the load case picks the bearing. In pumps, valves and fluid power the fluid picks it first, and the load is applied afterwards. The compatibility check is not optional: the bearing material, the plug lubricant and the counterface all have to be verified against the specific medium, temperature and any entrained solids before a grade is fixed.

Media compatibility must be verified against the actual fluid composition, temperature and pressure before specification. This table is a selection direction, not a compatibility certificate.

4. Alloy selection

Where the pumped or process fluid is the environment and oil is not guaranteed, the alloy choice is driven by corrosion and wear as much as by strength. Composition and property tables live on the material pages; the roles below are the selection direction.

Grade details are on the alloy page, the leaded tin bronze, tin bronze and aluminium bronze material pages, and the PTFE composite page for the liner types.

5. When graphite or PTFE plugs fit

Valve and pump bushings are where the phrase “runs dry” is taken literally, and where solid lubricants earn their place. Graphite is the common choice for hot or dry service and for water-lubricated positions, because a graphite plug keeps a film on the counterface even when the only liquid present is the process medium or plain water. PTFE plugs or a PTFE composite liner are chosen where the lowest friction is needed, where the medium is chemically aggressive, or where a valve disc must break away easily after long static periods.

The distinction between them is set by temperature and chemistry. Graphite suits hotter and drier service but oxidises in air at very high temperature; PTFE gives very low friction and broad chemical resistance but is limited in load and must be verified against the actual medium. In a seawater or submersible pump, aluminium bronze with graphite plugs is a common water-lubricated combination; in a valve stem or trunnion that must move easily after long idle periods, a PTFE composite liner is often specified.

6. Hydraulic cylinder and fluid-power notes

Hydraulic cylinders are the exception in this industry in that the working fluid is the lubricant. The bearing duty is nevertheless demanding: rod-end and pivot bushings carry high, often shock, load through frequent reciprocation and oscillation, and they sit at the boundary of a high-pressure system where any failure is disruptive. Cast bronze is the conventional rod-end and clevis bushing; graphite-plugged bronze is used where a greased pivot is impractical; and steel-backed bimetal is common in high-volume, high-load actuator positions.

Two hydraulic specifics matter. First, the bearing is selected alongside — not against — the rod seal, so bore and clearance are set to keep the bushing concentric and stop it loading the seal. Second, in fluid-power linkages the bushing often oscillates through a small angle under load, which is again the condition a graphite-plugged bronze handles without an external film. See the PTFE composite bearings page where low-friction, low-maintenance hydraulic pivot duty points that way.

7. What to specify on a drawing

• Alloy and standard Grade plus governing spec and year, e.g. C95800 to ASTM B505/B505M.
• Cast route and form Continuous, centrifugal or sand; split where installation demands.
• Lubrication Grease, oil, water-lubricated, or solid graphite/PTFE plugs — and plug pattern.
• Process medium Fluid, temperature, pressure and any entrained solids; confirm compatibility.
• Motion and load Rotation, oscillation or reciprocation; speed and whether load is continuous or impactive.
• Counterface Shaft or stem material, hardness and finish.
• Clearance Running clearance against the actual counterface and operating temperature.
• Code Any valve, pump or pressure-retaining standard the assembly must meet.

8. Frequently asked questions

Why are bronze bushings used in pumps instead of ball bearings?

Many pump shaft positions are lubricated by the pumped fluid rather than a clean oil film, and many run partially submerged or with entrained solids. A bronze bushing tolerates boundary or medium-lubricated running, embeds hard particles, and wears progressively. It is also the standard choice where the bearing must run in the process medium, which a rolling element bearing is not designed to do.

What is the difference between graphite and PTFE plugs in a valve or pump bushing?

Graphite plugs suit hotter, drier or water-lubricated service and keep a film on the counterface in the medium. PTFE gives very low friction and broad chemical resistance and is chosen where a valve disc must break away easily after long idle periods or where the lowest friction matters. Temperature, chemistry and load decide between them, and compatibility must be verified against the actual fluid.

Which bronze resists seawater in a pump or valve?

Aluminium bronzes such as C95500 and C95800 (CuAl10Ni5Fe4) have strong seawater corrosion and cavitation resistance among the common grades, and are a standard water-lubricated choice for submersible and marine pump and valve bushings, often with graphite plugs.

What bushing is used at a butterfly valve trunnion or shaft?

A shaft or trunnion bushing that must move the disc easily, often after long static periods in water or a process fluid, is commonly bronze with graphite plugs or a PTFE composite liner. The choice depends on the medium, temperature and how freely the disc must break away.

Do hydraulic cylinder bushings need to be self-lubricating?

Not always — the hydraulic oil is the lubricant, and plain cast bronze is the conventional rod-end and clevis bushing. Self-lubricating graphite-plugged bronze is used where a pivot cannot be greased, and PTFE or bimetal liners where low friction or high-volume load capacity is the priority. The bushing is also set up to stay concentric so it does not load the rod seal.