Hand pump issue

[MrP]

So I have a hand pump for my PCP. It is branded as Diana, but probably just the same as all the cheap ones. It’s behaving a little differently now than it was when I first got it. I’m still able to pump up my air gun just fine but it seems like there’s a little bit of back flow of air after I do each down pump. What I mean is when you’re pumping, and you are at the end of a down stroke, the pump handle rebounds a little bit when you stop pushing, I suppose due to some air pressure in the tube. What I am noticing now is that the amount that the pump handle rebounds has increased a good amount, which tells me that some larger amount of air is not getting pushed into the tank of the air gun compared to previously. I can push that last little bit of air in but it takes another push. I’m wondering if there’s an O-ring or a valve that’s failing somewhere and based on this characteristic where I should look in the pump to fix this? Or is it a matter of over lubrication or under lubrication? Instructions that came with the pump suggested it should be periodically lubricated with an oil that they provided. Translation is horrible so I can’t tell how often to oil it, Apparently you’re supposed to lubricate it either after the first 800 pumps or every 800 pumps. Not sure. 

Also based on the way the needle on the gauge is behaving it seems like the pressure is dropping slightly at the end of each pump as opposed to staying at the same level. Each next easily restores the slight drop so that tells me the loss of pressures in the pump and not in the air gun. Also there’s that telltale little click sound with each stroke that tells me the pressure is dropping slightly in the pump and the little “door” on the air gun tank valve’s foster nipple is closing.


Do any of you have any experience with this pump behavior and what (if anything) to do about it?

 

[Ducky1988]

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[ImpactX]

Been using a hand pump for 2 years. Been though many hand pumps. Cheap $35 Chinese pump to $160 Benjamin pump all the way to $280 hill pump. In times they will always get harder to pump. I made the switch to a compressor and will never look back at them handpumps anymore. It's true, once you go black, you don't go back lol. Get yourself a compressor. Even a $250 yong heng will be 100x better than a hand pump. You will thank me.

 

[Yo]

They are actually cardio and body building tools disguised as airgun pumps so you don't have to pay to go to the gym to add weights or increase tension resistance as you get stronger with enough use. Eventually you may even look like this! HE has been an avid airgunner too for YEARS!

 

[MrP]

Wow - it’s like looking in the mirror. You too can achieve these results. All you need is one pandemic-stricken economy, a garage, an airgun, and our amazing body building stirrup pump system.

 

[Aimright]

I have a Hatsan 3 stage hand pump that is probably the exact same unit as your Diana pump, basically a rebadged chinese pump. I have had to rebuild it a couple of times, the first time was maybe after about 5 uses, and the second time after about 10 uses. They are pretty easy to disassemble and after looking at a few you tube videos and a little other research on the web I just went for it. The first time I used the spares kit Hatsan provided with the pump, but many of the orings inside the kit were the incorrect size or so hard that I could not use them so I sourced a few from my local Ace Hardware store. At that time I basically just replaced about everything that looked suspicious and it seemed to fix the problem (similar to your problem) for awhile. But then shortly after that it experienced the same problem again, maybe after ten uses as I said earlier. That time I remember replacing most things again, but there was a little round rubber ball inside that I had not replaced before that was a little buggered so I did replace it along with some of the orings. I think the round ball acts as some sort of check valve. On this second rebuild I ended up purchasing this spare kit from Ali express that seemed pretty complete: https://www.aliexpress.com/item/32966875000.html?spm=a2g0s.12269583.0.0.54ae7def4fwXPi

So far it is still working, but since then I purchased a used SCBA tank my hand pump is relegated to an emergency backup. Yes, as shown above from the other posters, it is true, I have lost my Incredible Hulk physique and turned into a wimpy man with atrophied pecs and biceps since I stopped hand pumping , but my language has improved since I don't curse my handpump anymore!

Also wanted to mention I use 35 weight silicone RC shock oil to lightly lube the pump most every use, and go slow on my pumping giving it a rest every 4 minutes or so. That did not help me from having to rebuild it twice, but I still think it is good advice, particularly for minimizing moisture. 

My Hatsan handpump

Silicone oil I use, available at hobby shops that have radio controlled cars for about $4

Parts diagram off the internet.