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9-point checklist for impact sprinklers
Often overlooked when it comes to maintenance, impact sprinklers can get worn or damaged with time, which can greatly affect their ability to evenly distribute water.
To head off irrigation season repairs, Rain Bird International offers the following inspection guide for key sprinkler components. The company warns to never use oil, grease, or pipe dope on sprinkler heads. Oil causes bearing washers to swell and soften, which affects the rotation of the sprinkler. Pipe dope or thread lubricant contains oil, and when applied to the bearing threads, it gets carried to the washer, saturating it and causing the sprinkler to stop turning. If oil has been applied, it will be necessary to disassemble the bearing, wipe all oil off the sleeve and nipple, and replace all washers with new parts.
A detailed Rain Bird inspection guide can be downloaded from the Web address at the end of this article. Following is a short version of the guide.
1. Check system pressure. If the sprinkler is failing to rotate or is overly misting, check the water pressure at the nozzle's pilot tube using a pressure gauge. (Check with your sprinkler dealer to get the correct gauge.) Low pressure could indicate a blockage in the line. Depending on sprinkler model, some adjustment can be made at the sprinkler to correct for differing pressures.
2. Check for foreign matter in the nozzles. For nozzles that do not contain a stream straightener (a small vaned device inside the nozzle), you can use a pipe cleaner or coated wire to remove soft material while the sprinkler is operating. Avoid scratching the nozzle opening, however. For sprinklers with stream straighteners, remove the nozzle and straightener for cleaning.
3. Examine the sprinkler for damaged parts. Some components, such as a broken arm spring, may need to be replaced completely. But some cast bronze and aluminum parts, like sprinkler arms, can be bent back if they're not too badly damaged. In the case of Model 20 or Model 25 Rain Bird arms, a good rule of thumb is to bend them so that when the arm is at rest, the vane X-point is just to the left of the nozzle opening when viewed toward the nozzle face with the sprinkler in the upright position.
4. Replace broken arm springs. All broken springs should be replaced following manufacturer instructions. Test for proper spring tension by using an arm weight (available from your dealer).
5. Inspect bearing washers. Replace worn or damaged washers because doing otherwise could damage the more expensive bearing nipple and sleeves.
6. Inspect wear washers. These T-shape washers sit above the bearing washer and vary by sprinkler model. Replace worn washers to avoid bearing nipple and sleeve damage.
7. Check the bearings. Using a special wrench (available from your dealer) or a small bar or large screwdriver, check the sprinkler's bearing if that sprinkler does not rotate freely.
8. Examine the trip mechanism. This pertains to part-circle models only where the trip spring is about the only item that may need to be replaced after extended use. Check for lime deposits on the trip mechanism and remove them to avoid the mechanism from sticking in the future. You may need to replace the spring if it is worn or damaged.
9. Set part-circle friction collars. The friction collars on sprinklers control the arc of the circle of watering coverage. To examine, remove the collars using only your fingers — using pliers will cause the collars to lose their tension.