Maintaining the right amount of grease inside motor actuators that use grease for lubrication is a vital part of valve maintenance, and can save time and money by preventing problems before they happen. Inadequate lubrication is often the culprit in a malfunctioning motor actuator, and understanding how to effectively manage grease in motor actuators can be a simple way to keep costs down and to keep actuators out of the repair shop.
Motor actuators must have the correct amount and type of grease in the gear case to provide for trouble-free operation.
The first step is getting inside the actuator. Actuators have from two to four grease plugs to allow adding and checking the level of grease. The quality, quantity, and consistency of the grease in the actuator should initially be checked every 18 months, then at a frequency derived from the results. This inspection must be accomplished through these grease plugs.
Motor actuators are built to operate on the partial immersion principle. What matters is whether or not the "worm" is totally immersed in grease. This is to ensure that the efficiency of the worm/worm gear set is operating at its highest level, because this gear set is the most inefficient gear set in the actuator, operating at about 20% to 25%.
Due to the heat of the sun or system operation, the gear box is pressurized, which is why just filling up the gear box with grease causes the grease to push through the seals and into the motor windings and/or into the limit switch compartment.
To determine the correct amount of grease to add to a gear box, perform an inspection by using one of the many "fill and drain" plugs to ensure the worm is totally immersed in grease. When the actuator is mounted in a different orientation, the amount of grease needed to totally immerse the worm will change.
If your actuator is disassembled for repairs or rebuilding, these grease plugs should all be removed, cleaned, and reinstalled. Sometimes these plugs will be corroded in the housing and must be drilled out. Due to the metal chips that will fall into the grease, don't drill them out during operation. Instead, remove them during the rebuild when the inside is exposed.
The drive sleeve in an actuator extends through the housing on both the bottom and top sides. A seal is used to prevent leakage of grease at this penetration. The lower drive sleeve is held in place by a seal retainer, which is installed and removed, from the bottom of the actuator. This seal retainer is held in place by screws, bolts, or just a press fit on different sizes of actuators.
When the actuator is disassembled for repair or rebuild, this seal retainer does not need to be removed to fish out the seal and replace it. However, it should be removed to allow the rebuilt drive sleeve to be installed first. If the seal is installed first, and then the drive sleeve, there is no way to ensure that the seal is not nicked or rolled during the drive sleeve installation.
Grease in the main gear box will not flow into the clutch housing compartment of the actuator, so this compartment must also have grease added to cover the motor pinion/worm shaft clutch gear set. Fill this area just enough to cover the gear set-not too full.
The actuator can be mounted in any position since it has a totally sealed gear case. However, mounting positions that would cause vulnerable areas of the actuator (e.g., motor and limit switch compartment) to be saturated with grease in the event of a seal failure are not recommended.
The Right Grease
Use only the correct type when adding grease to your actuators. This means the grease must:
- contain an "EP" additive
- be suitable for the temperature range needed
- be water and heat resistant and non-separating
- not create more than 8% swell in Buna N or Viton seals
- not contain any grit, abrasive, or fillers
- not slump-preferred NLGI grade 0 to 1
- not be corrosive to steel gears, ball, or roller bearings
- have a dropping point above 316° F for temperature ranges of -20° F to 150° F.
In addition to the above, keep in mind that grease is made up of a filler (soap) and oil. Different types of fillers are used and not all types will mix well with each other. If you are going to add grease, use the same type of grease in the gearbox or ensure the new grease is compatible.
Regularly checking the level and quality of grease inside motor actuators will provide results that speak for themselves. Quite literally, proper lubrication makes a motor actuator function more smoothly, and keeps it lasting longer and working at maximum efficiency at very little cost.