Frame Oil System Operation

Frame Lubricant

In the compressor frame, Ariel recommends ISO 150 grade paraffinic mineral oil that provides oxidation, rust, and corrosion inhibition, and anti-wear properties - commonly called R&O oil. SAE 40 weight engine oil is also acceptable, but contains many unnecessary additives.

In limited circumstances and with prior approval from Ariel, cold weather installations may use multi-viscosity oils in the compressor frame if the oil supplier certifies the oil as shear stable. The viscosity of shear stable oil degrades less through use. Most oil suppliers certify oil as shear stable if viscosity degrades less than a certain percentage in specific tests. As a result, multi-viscosity oils are subject to a 30% to 50% shorter life than single straight grade oils.

Synthetic lubricants are acceptable in a compressor frame provided they meet operating viscosity requirements outlined in Table 6-4. Compounded lubricants are prohibited in the frame.

Viscosity

For cold ambient temperatures, design the oil system so the unit may safely start with adequate oil flow to the journal bearings. Successful operation may require temperature controlled cooler by-pass valves, oil heaters, cooler louvers, and even buildings.

The minimum allowable viscosity of the oil entering the frame is 16 cSt. Typically, this is the viscosity of ISO 150 grade oil at about 190°F (88°C).

Oil Pressure

The factory sets normal pressure on the discharge side of the oil filter at 60 psig (4.1 barg) for compressors tested mechanically complete (inspector tag displayed). If factory tested as mechanically incomplete (no inspector tag), the packager sets normal oil pressure at initial start-up to 60 psig (4.1 barg) at the lower of the frame or cylinder rated speed, or driver speed at normal operating temperature.

Ariel uses the pump safety relief or separate lube oil pressure regulating valve to regulate pressure into the compressor. If oil pressure into the compressor at minimum operating speed and normal operating temperature does not read about 60 psig (4.1 barg), adjust the pump safety relief or separate lube oil pressure regulating valve. With compressor running at minimum rated speed, turn the adjustment screw clockwise to increase oil pressure, or counter-clockwise to decrease it.

The compressor requires a 45 psig (3.1 barg) low oil pressure shutdown for protection.

NOTE: If oil pressure drops below 50 PSIG (3.4 barg) when crankshaft speed equals or

exceeds minimum rated operating speed, find the cause and correct it.

Oil Temperature

Maintain frame inlet oil temperature as close to 170°F (77°C) as possible. Minimum lube oil operating temperature is 150°F (66°C) to drive off water vapor. Maximum allowable oil temperature into the compressor frame is 190°F (88°C). Higher temperatures increase the oxidation rate of oil. Every 18°F (10°C) within the operating range doubles the oxidation rate of oil.

For proper operation of the thermostatic control valve, the maximum differential pressure between the hot oil supply line and the cooled oil return line is 10 psid (0.7 bard).

Oil Maintenance

An oil analysis program is the most effective way to determine frame oil change intervals. Consistent oil analysis can identify when to change oil on the basis of need rather than a scheduled interval. Depending on service, oil analysis can significantly extend oil change intervals.

Install a sampling point between the oil pump and filter at an easily accessible location. Minimize dirt or debris that can collect around it. Use a needle valve to better control pressurized oil flow.

Collect and analyze oil samples to verify suitability for continued service. Oil analysis should include:

• Viscosity testing at 104°F (40°C) and 212°F (100°C). This verifies that oil has not mixed with cylinder

oils or process gas.

• Particle counting to the latest version of ISO 4406.

• Spectroscopy to determine wear metals, contaminants, and additives.

• FTIR (Fourier Transform Infrared Spectroscopy) to check for oxidation, water or coolant contamination,

and additive depletion. This is more important if the sump oil is not consumed by the force

feed system.