Bostitch RN45B driver/piston won't fire

8 years 8 months ago #1592 by chrisincolo
Bostitch RN45B driver/piston won't fire was created by chrisincolo
I just installed the o-rings (kit #RBK13) to fix the two that were worn in the head valve, and on the piston sleeve retainer, which stopped the leaking out of the exhaust port, further keeping the driver from retracting. However, when I hooked it up to air to test, all I got was a strong burst of air at the trigger valve each time I pressed the trigger. I took everything apart again to inspect for other damaged parts or contaminants...nothing obvious. So next I replaced the trigger valve (TVA-6) and took everything apart again, made sure to put air tool grease on all o-rings , and still the piston won't fire. It just allows air to escape out some kind of pressure-relief or bypass next to the plunger on the trigger valve only when depressed, not continuously. Tried increasing air pressure from 85psi to 100psi, to 110psi, to 120psi... still would not move the driver/piston. I have cleaned and inspected the entire gun several times now, and am at a loss as to why there is so much back-pressure at the trigger valve. The piston seems to move freely inside the sleeve; but, with a little more resistance than before the worn 0-ring was replaced.
I found your tech videos very helpful; but nothing addressed this particular problem. Please Help!

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8 years 8 months ago - 8 years 8 months ago #1598 by MTR-Admin
Replied by MTR-Admin on topic Bostitch RN45B driver/piston won't fire
Thanks for the post!

This symptom is very specific. It is an internal leak that can only escape when the trigger valve is opened, but due to this air loss, the tool will not cycle.

It is without a doubt the seal point of the outer diameter o-rings on the head valve piston. These o-rings seal between the head valve o-ring glands and the inside bore of the cap assembly.

By theory, it can only be the head valve, the OD o-rings, or the cap.

1) You already installed the o-rings from the kit! However, you may choose to try another new batch. It is not impossible that if the kit is old, the o-rings have shrunk a bit, and they are a loose fit design. If they shrink they can act like worn ones, however this is rare! O-ring numbers are MRG052526, 2 ea.

2) Severe wear in the o-ring glands (where the o-rings sit) of the head valve piston can cause air to leak behind the o-ring. This should be visually apparent if you look for it. This is not the most likely symptom, but if a lot of sand and grit were found in the tool, it could have scored this area.

3) The cap assembly (most likely based on work done so far). If the bore in the cap where the o-rings ride is severely worn/scored it is likely the o-rings cannot seal. Again sand and grit can badly score this area.

The bad news is that the cap is no longer available...

There is really no other area that can cause the symptom you're describing.

I hope this helps!

- MTR
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8 years 8 months ago #1602 by chrisincolo
Replied by chrisincolo on topic Bostitch RN45B driver/piston won't fire
Thank You So Very Much!
After taking the coil nail gun apart numerous times to figure out why it would not operate any more, I read your reply earlier today, which was a very thorough explanation of 3 possible causes. It turns out that each one of them was correct, in part. In addition, the attachment you provided, showing a cutaway view of a Bostitch gun showed how air travels around the piston, head, and other passageways (a picture truly is worth a thousand words).
Fortunately, the cap wasn't too badly scored, considering the age of the tool. I carefully studied the o-ring surrounding the head valve, and observed that indeed it was not tight inside the bore of the cap.
Next I remembered that the o-ring kit (purchased from Amazon.com) came with no instructions, no parts schematic, and had extra o-rings that may have been for later models than mine. I discovered that the o-ring that I installed around the plastic head valve was slightly smaller in diameter than two remaining in the kit. The larger one fit a little loose in the groove, but I went ahead and tried it anyway. It works!
The problem with buying repair parts from retailers like Amazon.com, is that there is absolutely no technical support... you now have my business! Thanks again.

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8 years 8 months ago #1606 by MTR-Admin
Replied by MTR-Admin on topic Bostitch RN45B driver/piston won't fire
I'm really glad to hear this, all's well that ends well :cheer:

You're right, that's the caveat when purchasing from Amazon and the like; I certainly do and it's fantastic for many purchases, but sometimes it's good to have the knowledge of an industry person with these technical parts/issues.

Thanks again for posting!

- MTR

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3 years 4 weeks ago #3605 by DougT
Replied by DougT on topic Bostitch RN45B driver/piston won't fire
Thanks for the reply, sorry don't mean to hijack this thread. i have a similar problem with my N60FN, have replaced trigger valve and all seals,  $$$. I believe head valve is the issue. I have 2 o-rings in the headvalve, 1 on the outside and 1 on the inside that "seals" the plastic part that is pressured by the spring. I cannot find anywhere the function of that part/seal. All i get when i press the trigger is the normal air out of the trigger, no movement of the piston. I have probably taken apart this gun 30+ times. Ready to give up and buy another nailer. Can't detect any "grooves" or wear regarding that headvalve.

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2 years 7 months ago #3643 by marcler
Replied by marcler on topic Bostitch RN45B driver/piston won't fire
Thanks for helping with this question!

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