Yong Heng - 'Humming Bird' Needle Issue

[explosive]

Hi everyone, this is my first post as I am new to this fine forum (but not new to airguns). I'm CZ-Sniper on airgunforum.ca. 
So the Yong Heng was doing its first fill, which was on a 90 cubic inch Ninja bottle, attached to the Tuxing oil/water Separator. The needle on the YH's gauge was moving fine when the pressure started to climb and equalize with the bottle's but then as it started filling up the tank, especially closer to the 4500 PSI mark, the YH's needle started to vibrate so much that it was creating that humming bird effect and rendering it unreadable, so I had to resort to looking at the bottle's pressure gauge, which did fill it up to 4500 PSI without a problem. 
Any idea what's going on or how to dampen/fix this issue?
I'd appreciate any input you have, thank you.
Al

 

[frank320]

there's probably a leak somewhere between the compressor gauge and foster output valve.
Check your Tuxing oil/water separator, YH filter for leaks, check the o-rings, etc...
Leak is occurring at a higher pressure, i.e when the gauge needle starts "vibrating", that is when the leak is happening, above that pressure.

I had that issue, found a leak at the output filter. Replaced the o-ring and all was fine after.

 

[Centercut]

Another possibility is that the "oil" was drained from the gage when they shipped the compressor to you. Is it fluid filled? If not, take a look at the gage and see if it has the rubber stopper plug located on the side of the gage. If so, that means its supposed to be fluid filled. Use glycerin or silicon oil (clear fluid) to fill...

 

[explosive]

@Frank320, thank you. I made sure everything is in place and I did have to tighten some stuff up there, so I'm sure that will help! 
@Centercut, bingo! Rubber stopper confirmed. Oil drained out from the factory like you mentioned. I ordered the following silicone oil. I hope it's the right viscosity and is appropriate for a high pressure gauge. Thank you all for your help. I will fill up the gauge and provide an update shortly.

 

[Centercut]

That should work fine. Glycerin, silicon oil, light hydraulic fluid, they all work the same in a non-critical application like this. As long as its a clear liquid so you can see the needle...