(I didn't get into editing the first run of this post in time,and I didn't get the last pic small enough - here is the rest of the story)
I was suspecting that only the third stage fails in these pumps - most of the time. And based on my recent findings in this rebuild I am concluding: this is true - the third stage fails first - most of the time.
My pump was locking up at about 500 psi; couldn't push the handle down nor pull it up - stuck in the middle. The ambient temp was 62 degrees. After the third stage rebuild it worked perfectly in 94 degree weather.
The good news is: it was very easy to rebuild (only the third stage). All you need is a small flat blade screwdriver and two common wrenches. The O-ring gets destroyed and I got a substitute from Ace Hardware: #36,,,5/16 X 3/16 X 1/16 ( a common O-ring used in water faucet repair.) for $0.69 (well actually I also bought some new lube listed below for about $5.00)
Benji and AirForce pumps are the same innards - only the output connectors are different.
I used a different lube on this third stage and I believe this modification has made it better than new - but only time will tell if this lube lasts longer. Moly lube was used in the manufacture of my pump and based on what I found looks to me that moly lube gets cooked as well as the O-ring. There was a lot of black gritty substance - more than what would be found if only the O-ring disintegrated. The O-ring was chaffed on the edges and it was leaking. What I believe happens is the compressed air after the third stage leaks back into the second and maybe first stages and locks everything up.
The lube I used is by Permatex and is called "Anti-Seize Lubricant" and its the stuff one commonly puts on spark plug threads of engines. It has a rating of 1,600 degrees F. I figured since we are dealing mostly with heat issues - it might work. It feels just as slippery as moly and with the same consistency. And the first time pumping up to 3K psi,,,,,it worked perfectly.
DaveShooter gave me a link to a Spanish forum which has all the pics one would need to do a complete rebuild (I don't think a complete rebuild is necessary most of the time). I am including 7 pics that will guide you thru what I did. Here is the link with all the pics for a complete rebuild
http://www.ballestaperu.com/comunidades/forum/33-taller-aemero/6257-mantenimientoa-inflador-benjamin.htmAnd here is what I did in seven easy steps:
Step 1: loosen the set screw on the bottom collar - don't have to take it completely out and you don't have to take off the round brass air filter.
Step 2: simply push the collar up on the shaft so you can get at the bottom large nut that takes the entire shaft out of the base. (Pic labeled step two shows the shaft out of the base already with the collar pushed up.)
Step 3: loosen that large nut and unscrew the entire shaft from the base.
Step 4: loosen the bottom brass transfer port from the shaft and take it off.
Step 5: using a sharp pointy object or perhaps needle nose pliers, take the spring and brass valve out of the transfer port
Step 6: take off the old O-ring and clean everything up. I used Q-tips and rubbing alcohol.
Step 7: reassemble as shown but with lube on the O-ring and valve, and spring too.
What I found in my pump was a corroded spring as well - from the heat and moisture. The last two rounds of my spring simply broke off. I couldn't find a suitable tapered spring so I clipped two rings of another spring the same size as the large end of the tapered spring and spread the rings out so the two ends would actually push against each other rather than get wound around each other. I was trying to get the approximate same length as the original spring. So, I slathered my entire spring with the Anti-Seize lube hoping it would protect it from heat and moisture, preventing more corrosion of the spring.
This was very easy to do, and needless to say I am very happy with the outcome.
