The bane of slab lifting equipment is the iso. It turns your hands black if you get it on them and it is the main culprit that causes pressure imbalances. For some reason, in the past few years the problem has gotten worse. I suspect is has something to do with changes in the chemistry of the raw materials.
Contractors who use their rig on a daily basis have less of a problem. If your rig sits for any length of time, the iso (A side material) can start to setup in the hose. We see this most often at the end of the whip hose right next to the gun. The solution is simple, but you have to be vigilant. Make sure you have greased up the threads on the A side drum, change your desiccant drum cartridge when the desiccant changes color, and follow the instructions below to recirculate the A side material every 10 days that your rig sits unused.
Use the drum pump to shoot some A-side material into a waste bucket. When the material coming out of the hose looks clean, move on to step 2. It shouldn’t take long.
Re-circulate the material through the hose back into the A-side drum. Use a paint filter bag or panty hose to strain the material. This will prevent any cured iso that has formed in the hose from getting back into the drum. Do this step for 5 to 10 minutes (more if you have a lot of hose and less if you only have one or two sections).
Make sure your drum is closed up tight with white lithium grease on the threads. Same with the plug on the end of the hose.
You can pump the A side material using only the drum pump. However, if the pump sits for more than a couple of weeks you will want to also fire up your proportioner for a couple of minutes at low pressure to make sure you have fresh iso in the pump cylinder as well. To do this you will need to recirculate the B material at the same time.