Well I found that one of the check valve of the cylinder is probably broken on the sled. (thanks to sinjin588 who send me the troubleshooting spec) The troubleshooting pages talk about "mity vac" to check and test all the check valves. they should pop off about 2-5 psi!!! Did any body as already use or heard about this tool? Where I can buy one? Is it cheap? Thanks!