Hill Mark3 Pump Rebuild Question

Hill doesn't publish the sizes and in 10+ years of activity in the online airgunning community, I have found only passing mention from others that usually do not distinguish between the different pump versions over the years (i.e. MKI - MKV).

But with that said, a user on GTA stated his pump uses a -005. I fixed my pump with a -007 (a MKII, I think). Over the years, I have repaired a couple dozen pumps of various makes and models, and it was always a -005, -006, of -007 on the final stage. So for about $4 + shipping, you could get a couple of each size. Or measure the piston OD and groove diameter with calipers and extrapolate the proper size. Post back if you need help with that.
you mean dash sizes 5,6 or 7?.a new o ring with me measure OD 5.85,CS 1.69 and ID 2.34 mm using a electronic vernier which frankly doesnt fit the dash sizes mentioned?
 
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Those dimensions are a close match to a -005.

Basing that on the cross-section being very close to 0.070", which excludes the metric families of 1.5mm and 2mm since they are each about ten thousandths smaller or larger, respectively. So with it established as being in the "dash" family of standard O-rings (-00x), the closest match is a -005.
 
i think you are right...this is the approx size courtsey the OLYPSYS android free app...0005 size is the nearest best measure.are these NBR 90?

o ring 1.jpg
 
compression?you mean inside the pump
Just referring to the compression of the rings between the ID and OD, not air compression. Slightly larger (1.78 vs 1.69 as measured above your post) would be preferred rather than slightly smaller. Obviously, the measurements need to be fairly close all around to do the job properly and allow the O-ring to last.
 
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Will using dry pac content from another manufacturer (dessicants) have any adverse impact for my hills mk 3 pump...i mean there are cheaper dry pac granules available including colour changing media...as such ivee been forced to rehaul this pump after o nly 3 pumping sessions lately because of massive rains in my area(monsoons) inspite of the hills dry pac .Im enclosing a photo of one such colour changing bead dessicant....whats the advice

dessiant.jpg
 
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No particular alignment needed and you can use different dessicant. It is supposed to dry the air going in to the pump but the amount of rust and corrosion I found in my pump after a few uses prooves that the "in air" dessicant does very little to dry the air. The "out air" filter and drier I have on my china pump produces drier air for the gun and doesn't rust even though I have moisture building up in the pump.
 
Going through a rebuild & struggling too... keep blowing out the green orings. Did get a few to work ok & then it was like the check valve was stuck - looks like the other orings are done.

One question... note how hill give you the brass tip & not the o-ring..... is the brass possibly wearing, causing a decrease in diameter & causing extrusion?
 
That is a plausible reason, unfortunately it would be hard to confirm without knowing the manufacturing tolerances.

But there may be another solution. My advice is ditch the green OEM O-ring and go with a cast (aka Disogrin) polyurethane in 90 durometer. I don’t know the durometer of the OEM one but it’s supposedly HNBR (hydrogenated Buna-nitrile), and everywhere I looked it only appeared to be manufactured in 70 durometer. What I’m getting at is if your green seals are blowing out, it may be because they aren’t hard enough.

Having experimented over the years with a number of different materials for the final stage O-ring, I’m convinced that 90 duro cast poly is the cat’s pajamas.
 
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