Benji pump - handle pushes up on its own

[nervoustrigger]

I searched for information on this issue and came up empty.  The common failure is the small O-ring on the center piston, in which case the pump handle is hard to pull up.  Well, my issue is just the opposite...the pump handle wants to rise up on its own. 

I figure it has something to do with one of the check valves because when I pull up the handle, it doesn't want to draw in air.  Normally on the upstroke I hear a pronounced hiss as air rushes into the dessicant canister I put on the intake.  It does draw in a little air, but it's obvious it is not as much as usual because I don't meet as much resistance on the downstroke.

This is a recent rebuild and the only thing I can name that I did differently was to lubricate the rubber ball that serves as the upper check valve.  It was bone dry.  Is that a no-no?

[darren]

Jason there are two ball checks I believe..(I could be wrong, ask my wife)
the handle in the up position is usally  the 3rd stage check ballbeing stuck

best of luck

Darren

[nervoustrigger]

Thanks Darren.  I'm pretty sure there's only one ball check valve plus a brass check valve with an O-ring.  I had it stripped down completely.  Just knowing it is likely one of the check valves is enough for me to go in and investigate.

[nervoustrigger]

This gate doesn't get a lot of traffic but I guess I'll post a quick update.

I pulled the pump completely apart earlier this week and inspected all the seals and check valves.  Everything looked good so I just removed the lube from the ball check since it was dry when the pump was working normally.  No change when I put it back together.  Still builds pressure up to 3000psi, but what I have to do is practically yank the handle up to get it to take in gulp of air on the intake.  If I don't, the handle pushes up on its own and the intake does not pull in any air.

What I noticed is that when I removed the lower check valve (conical plunger with O-ring), the trapped pressure holding up the pump handle evacuated.  The spring looks fine, the plunger and O-ring look okay, the area is clean...nothing out of the ordinary that I can tell.  Before reassembly, I cleaned and used a light oil on these parts instead of the grease I used the first time in case it was so viscous that it was making the parts stick.  But alas, no change.

Any ideas, guys?

I ordered an O-ring kit from Mikgoo on the GTA classifieds to just go ahead and reseal the whole thing and see if it returns to its former glory, but I sure would appreciate any insight.

[FuzzyGrub]

Make sure you replace o-ring #8 with a white urethane one. 

[Roadworthy]

Jason - I'm sure you know Sun Optics rebuilds Crosman  - Benjamin pumps.  They also sell seal kits.  You might see if they have answers.

[nervoustrigger]

Actually, I did talk to the designer on Friday.  I had installed a complete new set of 90D O-rings a few days ago but it was still failing to take a gulp of intake air on the upstroke.  Took it apart again and carefully inspected all the O-rings under magnification and they looked fine.

I was suspecting the fat O-ring (a -210 as I recall) at the top because it looks like it is supposed to move up and down to seal against its seat on the upstroke but allow air to bypass on the downstroke.  In other words, acting as a sort of check valve.  Sure enough, the guy at Sun confirmed my suspicions.

It looked to me like the relatively stiff 90D material did not want to slide freely in its sloppy groove.  I replaced it with a softer one and I was able to use it yesterday to fill one 13ci Ninja bottle from empty to 3000psi and another from 2000-3000psi without a single hitch.  Every single stroke was consistent.

Suffice it to say I am happy to have it working again, having taken this thing apart probably 10 times now.  That's not an exaggeration.  The softer O-ring is from a Harbor Freight assortment so I don't expect it to hold up to the abrasion for long.  I'll just use it and enjoy it for now and go back with a 70D polyurethane or viton type when it gives up.

[nervoustrigger]

Fuzzy, it is indeed wearing a polyurethane O-ring now on the inner piston.

[nervoustrigger]

I spoke to Duane at Sun again and explained my observations and he confirmed that a 70D is what he recommends for the -210 O-ring.

That helps my confidence a bit.  Hopefully this puppy will hold up for a while now.

[nervoustrigger]

Just posting to confirm the pump has been working well under frequent use since I repaired it 3 months ago.

Namely, the large -210 buna-N 70A O-ring is still working despite rubbing against the pitted inside wall of the outer tube (pump was bought used and abused).

And the -007 polyurethane 90A O-ring on the inner piston is holding up. 

To give some idea about usage conditions:
1.  I pump in sessions of 60 strokes
2.  would say I average 1 session of pumping per day (sometimes 5 times in one day, and may go 5 days without pumping)
3.  there's a 1 liter bottle of dessicant on the inlet

[crosman999]

Its the o-ring in the 3rd stage,search youtube for the video that's in Spanish.

[nervoustrigger]

Actually, no.  Failure of the 3rd-stage O-ring (the -007 at the base of the inner piston) causes a symptom which is the opposite of what I was experiencing.  In that case, the pump handle doesn't want to pull up.  My issue was that the handle would shoot up on its own.

[Sfttailrdr46]

  My Hill Pump did the same thing if I was pumping up one of my rifles and stopped to rest the pump  but after a few uses that stopped happening so I just chalked it up to pump break-in Now have a Guppy and Freedom 8 so pump is relegated to emergency only use 

[nervoustrigger]

Ah, come on now, Don.  Did you come here to share your experience with your Hill pump?  Or is this a stealth gloat about your compressor and tank? 

[crosman999]

Ball valve should be dry. The video I sent shows how to disassemble the entire pump,it was useful to me when I rebuilt mine because I couldn't figure out how to get to the 3rd stage.

[amb5500c]

Just a reminder to you folks working on your pumps. Never use ANY hydrocarbon/petroleum based lubricants. They can and will blow up, and can cause severe injury or worse.
Richard

[Sfttailrdr46]

Ah, come on now, Don.  Did you come here to share your experience with your Hill pump?  Or is this a stealth gloat about your compressor and tank? 

I guess Both so guilty as charged . Come on now you have to admit it was almost subtle 

[Mark Mowrey]

I still haven't gotten my pump working that is exhibiting this same problem as I posted in the following thread:

http://www.gatewaytoairguns.org/GTA/index.php?topic=62575.0

I replaced the 210 o-ring with one from the local hardware store but that did not work.  I have no idea of what the hardness is.  The confusing part for me is that this is why I took the pump apart in the first place, it didn't start AFTER replacing the 210 ring.  I think I have one more option before ordering some 70A durometer rings.  On my first disassembly (I think I am on number 6 now) I ran all of the parts through an ultrasonic cleaner.  I wonder if I got it super clean and did not get enough silicon grease on the 210 ring upon reassembly to allow it to move properly. I will try to put the original factory 210 ring back on and make sure I lube it well.

Based on my examination, it is actually a vacuum in the outer chamber pulling the pump handle up.  I think it pulls (not worthy) air in to the outer chamber on down stroke.

[chancers]

I still haven't gotten my pump working that is exhibiting this same problem as I posted in the following thread:

http://www.gatewaytoairguns.org/GTA/index.php?topic=62575.0

I replaced the 210 o-ring with one from the local hardware store but that did not work.  I have no idea of what the hardness is.  The confusing part for me is that this is why I took the pump apart in the first place, it didn't start AFTER replacing the 210 ring.  I think I have one more option before ordering some 70A durometer rings.  On my first disassembly (I think I am on number 6 now) I ran all of the parts through an ultrasonic cleaner.  I wonder if I got it super clean and did not get enough silicon grease on the 210 ring upon reassembly to allow it to move properly. I will try to put the original factory 210 ring back on and make sure I lube it well.

Based on my examination, it is actually a vacuum in the outer chamber pulling the pump handle up.  I think it pulls (not worthy) air in to the outer chamber on down stroke.

Yeah, my Benjamin pump continues to give me trouble.  I cleaned and lubed it (put in brand new 90 durometer A oring and changed the part #5 210 O-ring).  I was having the pump handle go up on its own too.  After I changed the 210 O-ring part 5, the problem seemed to improve slightly.  But, now I had difficulty with the downstroke.  In a fit of frustration, I packed up the pump and sent it UPS to Sun Optics. 

Luckily, my Hill pump is functional (though I am having difficulty removing that pin that holds the pump handle connector to the innermost thin metal rod).  I got some advice from NervousTrigger ( and will try applying some PB Blaster to help loosen the corroded or rust pin).  We shall see.

[nervoustrigger]

I know this is an old topic but I was repairing one of these pumps recently and it would not take in air on the upstroke.  It's been a long time since I opened up a Benji pump so I just happened to take a look at Sun Optics' site and they had posted an updated manual somewhere along the way.  The pictures look like the same old poor quality ones they've always had but they now include a list of the O-ring sizes, and I noticed the -210 O-ring in the diagram above is actually supposed to be a -211.

As soon as I swapped it out, the pump started working like a charm.

Link to the manual: http://sunopticsusa.com/content/HP%20REPAIR%20INSTRUCTIONS.pdf