Originally Posted by Mike Leary
Most of the time a sticking stem (especially 12") is caused by improper installation and the landscape crew shoveling mulch over the heads. Once the heads are raised to grade, a little WD-40 on the risers will bring them back to working order. The RB wiper seals are the best in the business, IMHO.
Are you effin kidding me? Did you really just suggest spraying WD-40 on a spray head riser?
Any petroleum based product, WD-40 included will damage PVC. I'm sure that it will not do very well for the riser seal either. Clean the stem and the riser seal with water and make sure there is no sand in there. If either the seal or the stem are scored then replace them and make sure that the head is set to the proper grade.