392PA balanced valve

[Psipumper]

I have a working valve to test. Looks like it will be awesome from what I have seen so far. Heavy hammer spring is no longer needed to dump all the air.
Power should be over 45 fpe.

[Psipumper]

The balance chamber is retained by the spring loaded pin into the slot. The Rosetta  stone of the conversion .
The  chamber i.d. is .236”,the same as valve throat . The throat is chamfered at the valve seat to .270”.
Vent is through delrin at an angle. .025”

[Psipumper]

Photo of the standard arrangement it replaces. The balance chamber takes the place of the white spacer. Valve volume remains close to same.

[Rob M]

very impressive with these tiny tiny parts.. looking forward to the result as i know you have pushed the 39x to its limits with a conventional valve

[Psipumper]

Did make a lighter hammer. It has that pretty straw color. Material is O1. 35 grams . Has a rubber bumper sleeve around the front , not pictured.
I may go lighter if I can.

[Motorhead]

Now how cool is that ! ... balanced valve as a DUMP using a light hammer & spring.
very well applied 

[Psipumper]

Ran into a delay. I expected the weak point to be the oring groove but it broke here instead. I will order some PEEK to remake.

[Habanero69er]

Interesting. I'm staying tuned.   

[Motorhead]

Ran into a delay. I expected the weak point to be the oring groove but it broke here instead. I will order some PEEK to remake.

Helping hand ...

After drilling the hole for stem, measure the angle drill bit has and then grind the end of valve stem to the same angle.  This will lessen the stress on the poppet stem pushing on the surrounding material.
When square ended the stress is on the outer corners of contact and the root of the drilled hole will many times be the path of the fracture.

[Psipumper]

Ran into a delay. I expected the weak point to be the oring groove but it broke here instead. I will order some PEEK to remake.

Helping hand ...

After drilling the hole for stem, measure the angle drill bit has and then grind the end of valve stem to the same angle.  This will lessen the stress on the poppet stem pushing on the surrounding material.
When square ended the stress is on the outer corners of contact and the root of the drilled hole will many times be the path of the fracture.

Thanks for the advice. I did have the approximate drill angle on the stem. The depth of the stem hole was within one millimeter of the shoulder on the outside. Do you think drilling the stem hole 5mm deeper would keep a crack from forming across .

[Psipumper]

very impressive with these tiny tiny parts.. looking forward to the result as i know you have pushed the 39x to its limits with a conventional valve

I do want to do a good job adapting the technology to America’s pumper.
The balance for a dump valve pumper has different goals than a PCP. The chamber size and vent should encourage the valve to blow open . When I remake the poppet , I will reduce the vent hole to .013 (80 drill).
The more balanced the better. A light fast hammer then can be used to lift the poppet above the flow curtain as fast as possible then the valve should blow open on its own .
As I found out with the broken poppet,the light fast hammer is hard on parts. I would like to stay away from a brass poppet to keep it lightweight and unable to scratch the balance chamber bore.
Keeping the parts lightweight with soft rubber cushions at the end of stroke will make improved accuracy and lock time.
I do plan to test higher power levels but  after that I will limit it to 14 pumps.

[Motorhead]

Ran into a delay. I expected the weak point to be the oring groove but it broke here instead. I will order some PEEK to remake.

Helping hand ...

After drilling the hole for stem, measure the angle drill bit has and then grind the end of valve stem to the same angle.  This will lessen the stress on the poppet stem pushing on the surrounding material.
When square ended the stress is on the outer corners of contact and the root of the drilled hole will many times be the path of the fracture.

Thanks for the advice. I did have the approximate drill angle on the stem. The depth of the stem hole was within one millimeter of the shoulder on the outside. Do you think drilling the stem hole 5mm deeper would keep a crack from forming across .

Sharp corners  are nearly always stress risers, so thats a given.   @ 1 mm or .040" is not much being we know Acetal polymers are fairly resilient.  If you make it from PEEK be sure your TIR is dead nuts and pre lap the seat before assembling.

* You may have issues with PEEK being your starting at Zero pressure and unless the poppet / seat interface is dead nuts accurate it's not likely to seal at Low pressure.

[Rob M]

question.. why not vent right through the stem and take some load off the balancing piston? I might have missed something , im just thinking that your porting bore size to the balance chamber migtt be less critical since its essentially blow open..

[Psipumper]

https://hardairmagazine.com/wp-content/uploads/2018/12/HAM-Balanced-Poppet.jpg
The vent is drilled through to the throat now . I could drill a hole the entire length of the stem, then the balance chamber would be atmospheric pressure all the time.  I did not drill this stem because I am using hardened drill blanks.
With a  small diameter vent it will be easy to crack and slow to react.

[Rob M]

I dont actually know the functional difference between venting to the rear of stem or to the transfer port area.  But ive noticed most functioning like that diagram.. may have to do with backpressure from the shot reseating the poppet?

[Motorhead]

I dont actually know the functional difference between venting to the rear of stem or to the transfer port area.  But ive noticed most functioning like that diagram.. may have to do with backpressure from the shot reseating the poppet?

 Absolutely !!!!

While a force reduction valve DOES open easier it also lacks in similar ratio the ability to close.  Venting to atmosphere there is no effort exerted within the opposing end of primary seat within the chamber and valve will easily be held open until all air is expelled.  Vent to the valve throat and a high percentage of the pressure ( tho very little volume ) that leaves under the poppet filling throat back travels and pressurizes the balance chamber giving energy to the closing cycle for the micro seconds in time there is pressure within the valve throat and pellets not launched yet.

[Psipumper]

I dont actually know the functional difference between venting to the rear of stem or to the transfer port area.  But ive noticed most functioning like that diagram.. may have to do with backpressure from the shot reseating the poppet?

 Absolutely !!!!

While a force reduction valve DOES open easier it also lacks in similar ratio the ability to close.  Venting to atmosphere there is no effort exerted within the opposing end of primary seat within the chamber and valve will easily be held open until all air is expelled.  Vent to the valve throat and a high percentage of the pressure ( tho very little volume ) that leaves under the poppet filling throat back travels and pressurizes the balance chamber giving energy to the closing cycle for the micro seconds in time there is pressure within the valve throat and pellets not launched yet.

At first I was going to vent to the hammer area for full time atmospheric. But after drilling with the 1 mm drill awhile , I abandoned my original plan. I should probably go back to it because it is the best in this application.

[Rob M]

thanks Scot.Makes perfect sense ..

.Charles ,,, in this case that might be best since you dont want it to reseat before the valve has emptied.. interesting new challenges in a pumper dumper design. although on the other hand reseating may be a seperate  issue altogether

im planning to use these on a big bore balanced valve design


4mm o.d and should be strong
dont know if that would work on a smaller design

[Psipumper]

thanks Scot.Makes perfect sense ..

.Charles ,,, in this case that might be best since you dont want it to reseat before the valve has emptied.. interesting new challenges in a pumper dumper design. although on the other hand reseating may be a seperate  issue altogether

im planning to use these on a big bore balanced valve design


4mm o.d and should be strong
dont know if that would work on a smaller design

Thanks for the lead on that tubing. I did find some on eBay. 3/32 with a .023 hole  stainless steel. Exiting the vent all the way to the hammer area shouldn’t be a problem now. Back pressure wise the diameter of the vent hole won’t matter. I will drill it .013 thru the poppet still because it may act as an air cushion . Could cushion better with a smaller balance chamber  though.
I am also making another lightweight hammer in the 20 gram range .
A stock 392PA hammer is about 63 grams.