Air Venturi Air Venturi / Hill MK5 hand pump issues

[Red Pepper]

I've been using my Mk 5 hand pump for a few years without any issues, but recently it started acting up: trying to go above 2000 psi or so, it pushes down with high difficulty, then pushes back. I rebuilt the pump with the Hill rebuild kit, but without fixing the issue. I cleaned the two balls as well and ran a pipe cleaner through the holes to ensure they weren't plugged up. No success, and I haven't been able to find any way to contact Air Venturi or Hill about it. I bought a low-dollar pump off Amazon to get me through, but I would love to get this unit working again, as it's a nice pump and really doesn't have that much use on it. Any ideas on what to check? Thanks!

 

[Danman]

I've been using my Mk 5 hand pump for a few years without any issues, but recently it started acting up: trying to go above 2000 psi or so, it pushes down with high difficulty, then pushes back. I rebuilt the pump with the Hill rebuild kit, but without fixing the issue. I cleaned the two balls as well and ran a pipe cleaner through the holes to ensure they weren't plugged up. No success, and I haven't been able to find any way to contact Air Venturi or Hill about it. I bought a low-dollar pump off Amazon to get me through, but I would love to get this unit working again, as it's a nice pump and really doesn't have that much use on it. Any ideas on what to check? Thanks!

Good day, I have the same pump. Sounds like your little green (stage 3) o-ring is bad. Did you replace the whole piston or just the o-ring? I always lube pump shaft with the Hill grease but the 3rd stage o-ring I use silicone oil. It will pump noticeably easier, and the Hill compressor uses silicone oil and the EXACT same little teal colored o-ring for its 3rd stage.

 

[Danman]

What happens, I believe is it builds pressure but bc that o-ring is cracked and leaking-by, the pressure goes in the opposite direction and fights you trying to push it through the line and into the tank. Does you handle bounce right back up when it gets tight?

 

[Red Pepper]

The handle does bounce back up, but the o-rings are all fresh and in good shape (and greased). Unless I'm missing one somewhere.

 

[Red Pepper]

I replaced the whole piston (it came with the rebuild kit). Interesting idea using silicone oil...

 

[FL22]

Hello and welcome to HAM, although I see that you have been a member for a while.

@Danman ’s knowledge of this pump is solid and helped me with mine .

What Airgun(s) do you have?

 

[Danman]

The handle does bounce back up, but the o-rings are all fresh and in good shape (and greased). Unless I'm missing one somewhere.

I'd definitely strip it down and recheck the green o'ring. Hill sells the kit with the piston included bc often times the piston can get damaged if you've pulled up hard on the handle.....do not "max it out" on the up stroke. The bang it makes is the brass washer smashing the top of the piston. Do it enough times and the washer will slip down the piston and slice up the green o-ring in a hurry. Good pump but that is the weak link for sure. Hill needs to sell a 5 piece bag of those o-rings!

 

[Red Pepper]

I'd definitely strip it down and recheck the green o'ring. Hill sells the kit with the piston included bc often times the piston can get damaged if you've pulled up hard on the handle.....do not "max it out" on the up stroke. The bang it makes is the brass washer smashing the top of the piston. Do it enough times and the washer will slip down the piston and slice up the green o-ring in a hurry. Good pump but that is the weak link for sure. Hill needs to sell a 5 piece bag of just those o-rings!

I appreciate all your info! I'll pull it apart again and check that o-ring. It shouldn't be a problem, since I just replaced the piston and it hasn't worked well enough to use since, but maybe something went together amiss. At any rate, at least I know where to focus my attention. I don't pull it up hard, but I have typically pulled it fully up.

 

[Red Pepper]

Hello and welcome to HAM, although I see that you have been a member for a while.

@Danman ’s knowledge of this pump is solid and helped me with mine .

What Airgun(s) do you have?

Thanks! I have been a member for awhile, but I haven't needed to ask any questions or make any comments until now (although I do keep up with reviews/commentary of products I'm interested in). I have a Benjamin Cayden, Umarex Notos, Diana Bandit, and a Gamo CFX springer, plus a few CO2 pistols (and one ancient Daisy springer pistol I used while in college to improve my pistol skills for rimfire competition).

 

[FL22]

Thanks! I have been a member for awhile, but I haven't needed to ask any questions or make any comments until now (although I do keep up with reviews/commentary of products I'm interested in). I have a Benjamin Cayden, Umarex Notos, Diana Bandit, and a Gamo CFX springer, plus a few CO2 pistols (and one ancient Daisy springer pistol I used while in college to improve my pistol skills for rimfire competition).

Sounds good, so don’t be a stranger .

 

[Red Pepper]

Sounds good, so don’t be a stranger .

Thank you! I expect to be more active on this forum.