Hill MK3 fix

Home Forums General Compressors, tanks and pumps Hill MK3 fix

Viewing 8 posts - 1 through 8 (of 8 total)
  • Author
  • #22032

    After years of thrashing the Hill MK3 pump the high pressure seal (green) gave way.
    Replaced it with a new seal but surprisingly that too gave way on the first go!!!
    There goes another expensive seal.

    On careful examination under magnification I noticed the brass part had worn out areas and on measuring it showed the diameter to be 5.55 mm.
    Made another one to 5.9mm and that solved the problem for good.

    Will be writing to Hill to request them to include the brass bit with their seal replacement kit as this wears off before the seal.

    Hope this helps others,



    The OEM Green main pressure O-ring is a #005.
    The OEM Back Check Valve O-ring is a #006.

    I have been using these ones without a problem, they’re cheap as dirt !

    Main Pressure O-ring.

    Check Valve O-ring.

    Also a full reseal kit.

    ~ GKU


    Hello, need some help here !!!

    I tried to rebuild my MK3 after 3years of decent use with a kit from PA. I put together everything properly with good silicone lubricant (o-rings).

    When I attempt to pump now, pump rebounds after downward push. There is no need to pull up the handle and air is not being pumped. To pump any air, I have to hold the handle at low position for a while. I tried adjust/re-lubricating/wiping out the valve at bottom but no luck.

    What should I be checking next?


    It’s going to sound crazy but just to ask did you use silicone on the shafts of pump? I had the same issue until I lubed everything thoroughly. They say to use sparingly but I put quite a bit on everything and it started working as it should. I again to make sure we looking at same part the thin shaft that holds the green oring put silicone on the oring then slide it in and out to coat that shaft a bit more so oring doesn’t bind. Then when the pump is assembled when you pull up on handle you see the light gray tube you rub silicone grease all over that so the Orings in that glide better. You can see the light gray shaft have what looks like dry spots you want to coat it all that. I almost forgot when you take pump apart there are two small bb size black balls. Clean them and grease them up as well.



    Seems you have a problem with o ring No. 19. This one acts like a one way valve.
    Check again for correct dimension. If it is worn off or of smaller size the pump rebounds.
    The cylinder friction has to move it to work.
    Oversize within limits will work but undersize won’t.

    Rubber balls have to be clean and LUBE FREE.


    Thank you very very much Roland and Crunkjuice1. Works like a charm now!

    I kept adding silicone lube and tried fixed valve at bottom (#8 & #9) over and over in vain. Rubber balls had a lot of gunk, so did #19 o-ring.

    Refilling with a broken pump kept me worried during every shot. No more!

    GKU or any expert – is there a list of o-ring sizes on Hill MK3? Pyramyd’s $35+shipping is too expensive, can spend it on a bunch of pellets instead.

    Thanks again,


    Here are the sizes of most of the o rings in this version of the Hill MK3 pump.
    I tried to measure them as precisely as I could.


    As mentioned earlier I had written to Hill pump about the brass piston bit wearing away before the green seal.
    Also posted the worn off bit across for their own conclusion.

    I never got a reply but it is nice to see that they have taken heed of the suggestion as that was the achilles heel of the robust pump.

Viewing 8 posts - 1 through 8 (of 8 total)
  • You must be logged in to reply to this topic.