"Can you offer any advice about what type of single-point automatic grease lubricator is best for higher ambient temperatures (up to 55 degrees C) and dusty (desert) outdoor conditions with remote locations? What are the pros and cons of the gas-type and spring-loaded automatic grease lubricators? Which types are available for explosion-proof hazardous locations?"

Single-point lubricators offer many benefits, such as enabling lubrication in remote or restricted access locations, decreasing labor costs associated with using grease guns, allowing continuous or periodic lube supply over several months, reducing grease consumption and increasing machine reliability.

These lubricators are typically employed to grease bearings, but oil can also be used if the units are inverted. They are preferred in applications with limited temperature changes and vibration.

Spring-loaded lubricators often have a body made of polycarbonate for temperatures up to 250 degrees F or borosilicate for temperatures up to 450 degrees F. The discharge can accept different orifice sizes to control the grease flow rate. The volume is generally 2 to 18 ounces (60 to 532 cc) with pressures from 2 to 65 psi (0.14 to 4.48 bar). These units may be reloaded with a grease gun.

Gas-activated lubricators feature a low-pressure displacement (2-3 psi), which may not be adequate to overcome line resistance. Also, keep in mind that the hydrogen gas is flammable and prone to leakage. Most of these lubricators come in 4- to 16-ounce sizes, and some can be deactivated temporarily.

With positive displacement lubricators, a pump or piston controls grease or oil flow independent of resistance. These reusable systems operate on AC or battery power and feature a see-through reservoir. Many have multi-point capability. The discharge pressures may extend up to 900 psi. Some units are also approved for hazardous locations. While these types of lubricators can deliver more precise lubricant amounts than other technologies when the temperature changes or different grease consistencies are used, there is a risk of overlubrication. They also are not sensitive to ambient temperature changes or vibration. 

For the application described above, positive displacement lubricators may be the best choice, since they are less sensitive to grease consistency changes and pumpability due to the volume control maintained by the pump. For a dusty environment, you may consider systems that utilize cartridges to minimize lubricant contact with the environment during refilling. Explosion-proof models are also available for this type of lubricator.