I am using Cat 290 for engine
drive. Its been 4 years since I serviced the pump. Last week I blew a cup on a middle piston. I first noticed that flow dropped from over 2GPM to about 1.2GPM. Pressure was still holding but pulsations increased severely. I took it apart and verified that a middle piston hot cup was blown. The other two were also about to go. Hot cups are longer and are integrated with a metal ring. Not sure why i had the hot cup kit but that's what was in it since the beginning. Sales guy convinced me that i don't need hot cups since it's an RO application. So I replaced with regular cups. Regular cups are less than half of the length of the hot cup they don't have the integral metal part, and they can free play significantly more on the spacer. You can put tree regular cups in place of one hot cup to get the same spacing between retainers. That looked suspicious to me. I could not find any videos of actual installation
to confirm this. I put it back together to try, and now it wont build pressure at all, and flow is very weak to begin with before i even begin to build pressure. I am wondering if anyone can tell me what the problem might be. I did notices that cylinder inside walls are not perfectly smooth. I ordered the hot cup kit, and I also ordered the cylinders at 46$ per.