ZhongYan 4500psi high pressure gauge compressor is designed for pcp airgun cylinder, if you find the compressor is hard to fill a cylinder-the pressure can not go up 4500psi or go up slowly. Please check the screw, you can use some suds, you can find where is leaking easily and tighten it. Then try again.
If you can sure all the screws be tighten, and no leaking. You can try to clear the inner valve as follows:
1.Loosen the 4 screws
2.Loosen the 4 hex screws on the top
3.The topper can be off, and you can find the inner valve
4.Clear the inner valve, and make sure the o ring is well (the o ring will be damaged by high temperature)
5.Put back the valve to the notch on the topper, you can use some water or silicone oil to prevent valve falling
6. Please make sure that the valve is still sticked on the topper, then tighten all the screws
Try the compressor again, and i think the problem be solved. To know more details, you can just send email by firstname.lastname@example.org. Most professional service can be provided.