TargetTalk

My MK4 is acting up. Push pump down, but pressure kept popping back up.

Probably need to do a regressed and seal change.

Doe anyone have a MK4 break down diagram?

Try the link below.

http://www.airriflepump.com/acatalog/06 ... ctions.pdf

I had the same problem. I was never sure what the problem was. I thought it was a clogged micron filter. The gaskets looked fine to me. I applied silicone grease where recommended. I tried cleaning the filter (probably better just to get a new one) and cleaning out foreign particles where I could in the pump. After taking apart the pump and putting it back together a couple of times the pump started working normally again.

Found the problem.

There was a thin O-ring, in the inner tube. There is no description of that ring in the diagram.

After careful observation, what happened was that item 7, o-ring, got “circumcised” by the outer tube.

Any idea what is that o-ring size? It is the same size as item 8. But again no mention of o-ring size.

I measured once after buying a new repair kit, dimensions in millimeters.

Which one of the o-rings is the usual culprit for MK4?

That tiny green o-ring in the end of inner tube？or ??

Yes this little green oring is the main culprit, it causes the most frequent breakdowns.

Very frustrating. Bought the complete MK4 seal replacement kit
.
Changed all seals, lubricate where instructed, avoid lubrication where instructed.

Handle still popping up. Redo the whole process one more time. Handle still popping up.

If I go slowly handle just pop back up. No pressuring at all.

Only way to pump is by going berserk. Pump continually, angry man style, aggressively for 20, rest, then go berserk again.

Able to get up to 3000psi after 300 of those crazy, angry man pumps.

Any advice?

Have you replaced all the parts from the diagram also numbers 1 and 2?

Items 1,2,3,4,5,6,7,8,9,10,11,12 replaced

Problem solved.

Redid the whole o rings assembly all over again.

Handle still popping up.

Thought about the whole air entry, pathway and what not.

If handle is popping up, that means all seals are working.

This is a holding compressed air problem. That means item 1 & 2 is not doing its job. Or the Hill design is flawed.

Should I make that spring stronger, to enforce that diamond item 1 head seal back pressure closure? Tighten the screw as much as I can, that seal #1 is still not doing full closure, cylinder pressure back up into Hill pump, handle pops up.

Just remembered there is an original string taken out after replacement spring placement, so I stack those two springs together.

Aha !! Problems solved. There is strong closure from cylinder back pressure. No more handle popping up. Very easy pumping, pressure holding now.

Try this next time your handle is popping up.

If your pump leaks, it is seal problem. But if it pumps, but handle keep popping up, it might be weak spring problem. The original (and replacement spring) from Hill pump might not be strong enough.

Ah. Makes sense. Thanks for posting your discovery!