HPA Filter

The following two filters are common add-ons for Yong Heng : 

the big gold filter : https://www.aliexpress.com/item/32883123848.html?spm=2114.search0604.3.1.cac45129eSCuat&ws_ab_test=searchweb0_0%2Csearchweb201602_9_10065_10068_319_10059_10884_317_10887_10696_321_322_10084_453_10083_454_10103_10618_10307_537_536%2Csearchweb201603_53%2CppcSwitch_0&algo_expid=1cf8e25c-68d0-4385-bee9-e25313af9f2b-0&algo_pvid=1cf8e25c-68d0-4385-bee9-e25313af9f2b&transAbTest=ae803_4

the black filter : https://www.aliexpress.com/item/33047655100.html?spm=2114.search0604.3.38.cac45129eSCuat&ws_ab_test=searchweb0_0%2Csearchweb201602_9_10065_10068_319_10059_10884_317_10887_10696_321_322_10084_453_10083_454_10103_10618_10307_537_536%2Csearchweb201603_53%2CppcSwitch_0&algo_expid=03b96e6f-a793-47ad-b0f9-dc493e4f6cbd-5&algo_pvid=03b96e6f-a793-47ad-b0f9-dc493e4f6cbd&transAbTest=ae803_4

Just fill up the filter with 13X molecular sieve and plug up the two ends with a short segment of the cotton elements that come with the filter. 

The smaller black filter is preferred because it's smaller volume means that the time required to pressurize the filter is shorter. I have got the gold filter because the black one was not out yet when I bought my Yong Heng. At the end of a filling session, I use the compressed air inside the filter to blow out the water left in the coolant passage of the compressor so the bigger volume of the fitler is advantageous for me. 

If you fill your guns directly then there is really no need for any additional filter. Just use the small filter that comes with the compressor. There is no need for any molecular sieve. Just replace the cotton element inside after every 2 ~ 3 fills. That will keep the cotton sufficiently dry to absorb the moisture. Used cotton elements can be left to dry out by themsleves and reused the next time. They need be tossed when you see substantial oil stain on the outlet side of the element. 

Airgunfans, thanks for posting the links....very helpful.