| Pump Housing Material | Cast iron | High stiffness and good wear resistance; commonly used for mineral-oil hydraulic service. Typical operating temperature is approximately -20 to 100 °C, subject to the pump design. | General industrial machinery, mobile equipment, power units, and moderate-contamination environments. | Good choice for standard petroleum-based hydraulic oils. Verify corrosion resistance before using water-containing or chemically aggressive fluids. |
| Pump Housing Material | Ductile iron | Higher tensile strength and impact resistance than ordinary gray cast iron; suitable for higher mechanical loading when properly designed. | High-pressure or shock-loading hydraulic systems. | Useful where pressure pulsation, vibration, or mechanical loads are significant. The pressure rating must be confirmed for the complete pump assembly. |
| Pump Housing Material | Aluminum alloy | Low density and good thermal conductivity; often selected when compact size and low weight are important. | Portable equipment, compact power packs, and low-to-medium pressure systems. | Check resistance to abrasive contamination and pressure cycling. Aluminum is generally less wear-resistant than iron or hardened steel. |
| Pump Housing Material | Stainless steel | High resistance to many corrosive environments; common grades include austenitic stainless steels, but resistance depends on the exact alloy and fluid. | Food-processing support systems, marine environments, chemical service, and water-containing fluids when approved. | Select only after checking chloride concentration, temperature, galvanic effects, and the compatibility of gears, bushings, and seals. |
| Gear and Internal Wear Parts | Hardened alloy steel | High fatigue strength and wear resistance; surface hardness is commonly increased by case hardening or other heat treatment. | High-pressure operation, frequent cycling, and systems requiring long service life. | A suitable choice when fluid cleanliness and lubrication are controlled. Excessive particles can rapidly damage gear flanks and bushings. |
| Gear and Internal Wear Parts | Bronze or bronze-containing bushings | Good sliding properties and resistance to seizure under boundary-lubrication conditions. | Internal bearing surfaces in standard hydraulic pump designs. | Confirm compatibility with additives, water-containing fluids, and galvanically dissimilar metals. Bronze is not a universal solution for every biodegradable or fire-resistant fluid. |
| Shaft Seal | NBR (nitrile rubber) | Typical useful temperature range is approximately -30 to 100 °C, with short-term limits depending on compound and design. | Mineral hydraulic oils, lubricating oils, and many petroleum-based fluids. | Cost-effective and widely used. Resistance to ozone, weathering, aromatic solvents, phosphate esters, and some biodegradable fluids is limited. |
| Shaft Seal | FKM (fluoroelastomer) | Typical useful temperature range is approximately -20 to 200 °C, depending on compound, pressure, and speed. | High-temperature mineral oils, fuels, and many chemically demanding applications. | Generally good resistance to heat, oxidation, and many hydrocarbons. Confirm suitability for hot water, steam, glycol-based fluids, and certain fire-resistant fluids. |
| Shaft Seal | EPDM | Typical useful temperature range is approximately -50 to 150 °C, depending on formulation and service conditions. | Water-glycol fluids, water-based fluids, and some phosphate-ester applications. | Good resistance to water, steam, and many polar fluids. Do not normally use EPDM with petroleum-based mineral oils unless the specific compound is expressly approved. |
| Shaft Seal | PTFE-based seal | Very broad chemical resistance and low friction; temperature capability can exceed 200 °C in suitable designs. | Aggressive fluids, high-temperature service, and applications requiring low friction. | Requires correct energizing, shaft finish, installation, and pressure control. PTFE is not automatically suitable for dynamic sealing at every speed or pressure. |
| Common Hydraulic Fluid | Mineral-oil hydraulic fluid | Typical industrial viscosity grades include approximately 32, 46, and 68 cSt at 40 °C. Many gear pumps operate across a wider range, often about 10 to 400 cSt, subject to the manufacturer’s limits. | General-purpose hydraulic power transmission. | Usually compatible with cast iron, steel, bronze, and NBR or FKM seals. Confirm additive compatibility, viscosity at startup, and maximum fluid temperature. |
| Common Hydraulic Fluid | Water-glycol fluid | Water content can reduce lubricity and may increase corrosion risk; operating temperature and viscosity are generally more restricted than with mineral oil. | Applications requiring improved fire resistance compared with mineral oil. | Use only a pump specifically approved for water-glycol service. EPDM is often preferred for seals, but the exact fluid formulation and pump materials must be checked. |
| Common Hydraulic Fluid | Phosphate-ester fluid | Fire-resistant fluid with strong solvency characteristics; seal and coating compatibility can vary significantly by formulation. | Fire-sensitive industrial equipment and selected aerospace or process applications. | NBR may be unsuitable. FKM, EPDM, or PTFE may be used only when approved for the specific fluid and temperature. Check paint, hoses, and elastomer compatibility as well. |
| Common Hydraulic Fluid | Biodegradable synthetic ester | Often offers good lubricity and biodegradability, but oxidation stability, hydrolysis resistance, and seal compatibility differ among formulations. | Forestry, agricultural, marine, and environmentally sensitive applications. | Do not assume compatibility from the word “biodegradable.” Confirm seal material, maximum temperature, water tolerance, and the fluid supplier’s compatibility data. |
| Viscosity | Cold-start viscosity | Excessive viscosity increases inlet vacuum, noise, and drive torque. A practical target is to remain within the pump’s published cold-start limit and avoid cavitation. | Outdoor equipment, cold climates, and intermittent operation. | Select fluid viscosity for the lowest expected startup temperature, not only for normal operating temperature. Preheating or a lower-viscosity fluid may be required. |
| Viscosity | Minimum operating viscosity | Many internal gear pumps require approximately 10 to 20 cSt minimum at operating temperature, although the exact limit varies by pump speed, pressure, and lubrication design. | High-temperature systems and high-speed operation. | Too-low viscosity reduces internal film strength and increases volumetric leakage, wear, and heat generation. |
| Fluid Cleanliness | Contamination control | ISO 4406 cleanliness targets commonly used for hydraulic systems range from approximately 16/14/11 to 20/18/15, depending on pressure, component sensitivity, and duty cycle. | All hydraulic internal gear pump installations. | Use correctly sized suction and return filtration, maintain clean reservoirs, and prevent water ingress. Abrasive particles are a major cause of gear, bushing, and seal failure. |
| Pressure and Speed | Rated pressure and speed | Commercial internal gear pumps may be offered across broad ranges, commonly from low-pressure power units to approximately 250-300 bar designs; speed limits often range from several hundred to roughly 3,000 rpm. | System-specific selection based on flow, pressure, and duty cycle. | Never select from a maximum headline rating alone. Verify continuous pressure, peak pressure, speed, inlet pressure, shaft loading, noise level, and required service life. |
| Fluid Compatibility Check | Complete-material review | Compatibility must include housing, gears, bushings, shaft, coatings, static seals, dynamic seals, hoses, filters, and reservoir materials. | New fluids, mixed-fluid systems, and non-standard operating temperatures. | Request written compatibility confirmation for the exact fluid formulation, concentration, temperature, pressure, and seal compound before purchase. |
