| Compressed Air | 6–10 bar (87–145 psi) for many plant air systems | Approximately −20 to 80°C (−4 to 176°F), depending on seals | Choose a full-flow or high-flow design when pressure drop must remain low. Port sizes of 1/4–1/2 in are common for branch lines and tools. | Nickel-plated brass, stainless steel, engineering polymer; NBR or polyurethane seals | Suitable for general pneumatic tools, automation, and instrumentation when the fitting rating exceeds the system pressure. | Drain condensate and use clean, dry air. Do not use oxygen-service fittings unless specifically cleaned and approved for oxygen. |
| Water and Glycol-Water Mixtures | Commonly 4–16 bar (58–232 psi) in industrial and HVAC circuits | Approximately 0–90°C (32–194°F); freeze protection may extend the lower limit | Use a low-restriction bore for circulation loops. Size the fitting to limit velocity and avoid excessive pressure loss. | Brass, stainless steel, or compatible thermoplastics; EPDM seals are commonly used for hot water and glycol solutions | EPDM generally performs well with water and many glycol mixtures. Confirm concentration and additives before selection. | EPDM is generally unsuitable for petroleum oils and many hydrocarbon fuels. Check corrosion resistance for treated or deionized water. |
| Hydraulic Mineral Oil | 100–350 bar (1,450–5,075 psi) is common; higher-pressure designs are available | Approximately −30 to 100°C (−22 to 212°F), subject to the fitting and seal rating | Use a hydraulic-rated coupling with adequate nominal bore. Account for continuous flow, pressure spikes, and pressure drop across the valve poppet. | Carbon steel or stainless steel; NBR seals are common, with FKM used for higher-temperature service | Select using the maximum working pressure, not average pressure. Confirm impulse, burst, and connection ratings. | Never substitute a low-pressure pneumatic coupling. Pressure must be fully relieved before disconnecting unless the coupling is specifically rated for that function. |
| Water-Glycol Hydraulic Fluid | Often 70–250 bar (1,015–3,625 psi), depending on the system | Approximately −20 to 90°C (−4 to 194°F) | Flow capacity should be checked with the actual fluid viscosity, which can differ significantly from mineral oil. | Stainless steel or compatible plated steel; EPDM seals are commonly considered for water-glycol fluids | Verify seal compatibility with the exact fluid formulation, concentration, and corrosion inhibitors. | Do not assume a seal suitable for mineral oil will work with water-glycol fluid. Check galvanic corrosion when dissimilar metals are joined. |
| Fuel and Petroleum-Based Fluids | Usually 3–20 bar (44–290 psi) in transfer and service applications | Approximately −30 to 80°C (−22 to 176°F), depending on fuel and seal material | Use a bore large enough to prevent excessive restriction and vapor formation. For fuel transfer, consider flow-induced static electricity. | Stainless steel, compatible plated steel, or fuel-rated thermoplastics; NBR or FKM seals are commonly used | Confirm compatibility with gasoline, diesel, biofuel blends, aromatic content, and additives individually. | Use anti-static, bonded, or electrically conductive components where required. Avoid EPDM with petroleum-based fuels. |
| Mild Chemicals and Cleaning Solutions | Often below 10 bar (145 psi), but process systems may be higher | Typically 5–80°C (41–176°F), depending on chemical concentration | Evaluate chemical viscosity and the pressure drop caused by the internal shut-off valves. A larger bore may be needed for viscous liquids. | 316 stainless steel or chemically resistant thermoplastics; EPDM, FKM, or PTFE-based seals depending on the chemical | Compatibility must be checked against concentration, temperature, exposure time, and mechanical stress. | Do not rely only on a general material chart. Oxidizers, solvents, acids, and alkaline cleaners can behave differently at elevated temperatures. |
| Steam and High-Temperature Water | Commonly 3–16 bar (44–232 psi), with pressure-temperature limits carefully linked | Approximately 120–200°C (248–392°F) for many industrial services | Use a steam-rated, high-temperature coupling with minimal dead volume. Calculate condensate behavior and pressure drop. | Stainless steel or high-temperature steel; graphite, PTFE, or specially rated elastomer seals | Use only fittings specifically rated for saturated steam or the intended high-temperature service. | Pressure ratings often decrease as temperature rises. Standard pneumatic or general-purpose hydraulic couplings may fail rapidly in steam. |
| Vacuum Service | From atmospheric pressure down to the specified vacuum level; some designs support approximately −0.9 bar gauge | Typically −20 to 80°C (−4 to 176°F), subject to seal design | Internal leakage and dead volume are more important than nominal flow alone. Select a coupling designed to minimize air ingress. | Stainless steel, brass, or suitable polymer; silicone, FKM, or other vacuum-compatible seals | Confirm vacuum tightness, leak rate, seal permeation, and whether the coupling can be connected under vacuum. | Some quick connects seal well under positive pressure but allow unacceptable leakage under vacuum. |
| Breathing Air or Medical Gas | Application-specific; commonly 4–10 bar (58–145 psi) for distribution systems | Typically 5–50°C (41–122°F) | Prioritize stable flow, low pressure drop, and correct gas-specific connection geometry. | Materials and seals must meet the applicable cleanliness and gas-service requirements | Use only components approved for the specific gas and service classification. | Gas-specific connectors help prevent accidental cross-connection. Oxygen service requires controlled cleaning and compatible materials. |
| High-Purity or Corrosive Gas | Often 1–20 bar (15–290 psi), depending on the process and gas system | Commonly 5–60°C (41–140°F) | Use an internal geometry that minimizes particle generation, dead volume, and adsorption when required. | Electropolished 316L stainless steel; seal selection may include FKM, FFKM, PTFE, or other qualified materials | Specify surface finish, cleaning level, leak rate, and material compatibility with the exact gas. | Reactive, toxic, or oxidizing gases require dedicated engineering review, leak testing, and applicable regulatory controls. |
