Umarex "Umarex Notos Update HUGE power Upgrade!" Or is it?

[DiGuerra]

(...)
Moved probe shoulder back and thinned
Made a flat seat valve w/peek poppet
Poppet stem .078”

(...)
2 coils clipped from stock spring
Bored hammer then added back plastic spacers to make adjustments and lighten hammer. This thing barely has any hst adjustment travel.

(...)

Dave, you also seem to be onto something here regarding the valve. You mentioned a flat valve seat. Is it expected to have leak problems if the reg is set to a lower/normal pressure? Say, 120Bar/1750psi isntead of the 180Bar/2600 psi you mentioned?

And what is the logic of clipping the hammer spring and making the hammer lighter with such high reg pressure? I thought you would be having valve-lock issues at this point, so heavier hammer or/and stronger spring would be the solution... no?

Last question: Why thin out the poppet stem? Stock is 3mm, and you made it 2mm (0.078")... wont loads of air just escape through the hole? To what benefit?

I am VERY intrigued

 

[sb327]

A flat valve seat can be harder to get a good seal at lower pressures, yes. When made correctly with a correctly made poppet, it’s not a big issue. Tapered seats are more reliable and that is why they are produced that way…less returns. The trade off is a poppet that is harder to unseat. Flat is easier to unseat as well as using a peek poppet is easier to unseat (and harder to seal properly but when done correctly, not an issue).

Those two things allow for less hammer needed…clip the coils and you are back (sorta) where you were with less cocking force needed.

The smaller diameter stem works because I made a new valve and drilled that hole to match. The smaller stem decreases the closing force (and speed) of the stem/poppet while allowing more flow in the throat area. This allows a bit more dwell time.

That is a generalization of those changes, hope that answers your questions.

Dave

 

[DiGuerra]

A flat valve seat can be harder to get a good seal at lower pressures, yes. When made correctly with a correctly made poppet, it’s not a big issue. Tapered seats are more reliable and that is why they are produced that way…less returns. The trade off is a poppet that is harder to unseat. Flat is easier to unseat as well as using a peek poppet is easier to unseat (and harder to seal properly but when done correctly, not an issue).

Those two things allow for less hammer needed…clip the coils and you are back (sorta) where you were with less cocking force needed.

The smaller diameter stem works because I made a new valve and drilled that hole to match. The smaller stem decreases the closing force (and speed) of the stem/poppet while allowing more flow in the throat area. This allows a bit more dwell time.

That is a generalization of those changes, hope that answers your questions.

Dave

It makes sense! Thank you for taking the time!

I am new to PCPs and this PP750L has been an amazing gun to own and learn from.

Most mods so far have been very straight forward (porting, reg adjustments, etc) or just "plug&play" (plenums, barrels, etc), so i dont know if will risk the valve seat thing... Reliability and ease of use are one of the best things about this gun (and i dont have the skills or the tools to craft a whole new valve...if i mess up the stock one, i'll be in trouble ).

To be fair, I am already very surprised with what this thing has become in my ignorant hands! 25-30FPE? Those are the same kind of numbers i see on much higher end compact guns like Pathfinders, MicroHunters, Vixens, etc... And all of them are way heavier too (and most times bigger)
Sometimes I wish I had a reason to move to a "better" gun but, at least on paper, it doesnt seem to be worth it at all.