I have an 8 gpm pressure pro cold machine (around 400hrs). It has a 1" suction hose supply line with a plastic 1" valve in the line, going to a 200 buffer tank. When I am soaping, every now and then it sounds like the machine goes into bypass for a second then may run fine for several minutes. I don't hear it do it when it is in rinse mode. I have been using a VB-10 unloader, and replaced with a new one about a month ago and it was fine. I have also replaced all the check valves in hopes that was the problem. My hose clamps are tight, and I don't have any leaks on the pressure side. When the machine is in bypass mode, it doesn't surge (steady bypass for 5 minutes).

Any suggestions would be greatly appreciated!