How to Identify a Stuck Poppet
This video walks you through how you can check whether or not a poppet is stuck.
Take a T-Allen wrench - I'm using an 1/8" T-handle. Once your pressure line is off. you can put the T-handle into the port and it will go through the little flow control hole. And you should be able to get back in there to the piston. There's a spring behind it and has about a 1/2" of travel. It should go back in-and-out.
If you go in with the T-handle and it's just hard at the back of the travel, that is telling you that the piston is stuck. This happens very easily with the smallest bit of contamination.
At that point, you can pull out the flow control and get access to the piston and the spring. At this point, be very careful to note the orientation of everything so you can put it back in the same way. The spring will pop out at you, so make sure it doesn't shoot across the shop.
The piston can get stuck in the bore and it gets stuck in the bypass and the pump won't create pressure. So at that point, you can take this apart, inspect the piston and make sure it's clean with no scrapes or gouges. If they get stuck in there, they'll scar up a bit. You can polish and put it back in, if it's not damaged too badly.» View More Tech Videos