FX Pump Rebuild

[dgiannandrea]

I have a problem with the pump. It resists in both up and down strokes, does not pump. I have started disassembly, have rebuild kit on order, need advice.

The patient:

Brass "Large Piston" on the left is connected internally to black "main valve housing" right...

Large Piston with o-rings removed. Smaller o-rings appear to be shock absorbers.

Black "main valve housing." I used a piece of nylon tubing to protect the "valve pipe" while unscrewing. That work great.

I don't know how to proceed from this point. Advice please.

 

[RM100GUY]

I just rebuilt a Hill Mk4, I know it's a different manufacture, but I'll relate to you what I ran into the same problem you have after I resealed mine. I had to email Hill in England and they had the problem solved in two emails. Long story short I didn't change all the orings some looked ok, make sure you change them ALL, I replaced that 1 oring they recommended and it worked perfectly, make sure it is good and clean and follow FX's lube instructions. Hope that helps.

 

[dgiannandrea]

Can anybody with a pump manual provide the lube instructions. I'm the 2nd owner, no documentation came with the pump.

How do I disassemble the inner pump tubes??

 

[dgiannandrea]

I used water-pump pliers and the strap from a strap wrench to hold the large piston while turning the main valve housing:

and got separation!

I can now remove the 5mm bar (hi pressure piston) but the large piston is still connected to the 10mm hydraulic pipe...

There are two features on the large piston that need explanation.

The first appears to be a notch for a pin wrench, a matching notch is on the opposite side.On closer inspection, it appears to be an air passage as it passes through the brass collar into the O-ring land.

The second arrow indicates a hole (with matching hole on opposite side) that dead ends against the 10mm pipe. This might only be a transfer port for lubrication, nothing else comes to mind.

 

[mag13]

Have you checked these out? Maybe of some help looking at the drawings. Don't know which is your model pump but hope this helps.

http://www.fxairguns.com/wp-content/uploads/2014/03/Handpump-Drawing-and-partlist.pdf

http://www.fxairguns.com/wp-content/uploads/2017/09/FX-Pump-4stage-Turbo.pdf

 

[dgiannandrea]

Every day a new epiphany. (Using compressed air and four hands to find air passages)

Both holes are air transfer. The larger notches are fresh air intake past the double O-rings (removed) that act as a flap valve. The tiny holes on the right transfer air inside the large piston between the 10mm and 5mm tubes (downstroke.) That air then gets squeezed past the seals on the 5mm hi pressure rod/piston (upstroke) charging the hi pressure chamber.

I will get this verified then re-shoot the process for a final document...just in case I'm not the only one who needs to do this.

 

[dgiannandrea]

Yes, I am using the parts diagrams. It is interesting to note that both pumps are comprised of one piston rod and three tubes. The newer "Turbo" model has moved the large piston to the bottom of the next sized tube (upstream), while installing a "small piston" at the original location. Pretty much the same pump design with an additional compression chamber fitted in line in front of the small piston. I guess this explains the advantages of super charging pumps with compressed air: an external compression chamber.