Hill Mark3 Pump Rebuild Question

[anirudh]

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?

 

[nervoustrig]

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.

 

[anirudh]

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?

 

[F6Hawk]

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?

View attachment 437067

The cross section seems to be a bit off, but it might work with compression.

 

[anirudh]

The cross section seems to be a bit off, but it might work with compression.

compression?you mean inside the pump

 

[F6Hawk]

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.

 

[anirudh]

my hills mk 3 started to pump back..so was forced to replace the last stage o ring.i have changed 5 o rings of the last or 3rd stage(see attached photos) all of which to me appear to be ok without any damage.wonder whats the reason for this problem.