1750b strange HPA results

[UKStoo]

I recently built my 1750b ratty with 24" .177 barrel, on co2 (a 12g capsule) I'm getting 680fps with 7grn pellets for 7.2ft.lb, (I dont have any heavier pellets to see what its kicking out with them, at the mo)

now here's the strange thing,

On HPA (850 psi, but not confirmed yet) Im only getting 575fps...100 fps less...

Its running on HPA, through a GMAC caplet eliminator fitted with a male foster quickfill nipple down a curly hose and to the regged bottle.

its numbers are very consistant on HPA, within a 5fps spread over the 20 or so shots.

now the only things I can think giving the lower fps are...

1, its running a lighter hammer spring, lighter than the stock crosman hammer spring, which I made myself.

and

2, the fill nipple fitted to the caplet eliminator is fitted with a non return valve, which i left in place when I installed it.

Ive only shot it indoors so far where the room is a constant 20C and got the previous results, so the co2 should be around 850 psi, which should match the HPA reg.

Do you think ive completely fluked my hammer spring strength to give perfect co2 release at 20C? it doesn't mist co2 at all...or do you think the regulated pressure is a tad higher than the co2 and the hammer spring isnt opening the valve long enough? or could it be the non return valve is blocking flow (I doubt this one) restricting the output?

whats your opinions....

[UKStoo]

Anybody got any ideas?

[eric]

are you saying your numbers with hpa reg at 850 are lower the your co2 numbers ?  right off the bat the only thing i an think of  is everything is the same is that you have a leak somewhere . air is thinner than co2 so it will find places to seep that co2 can't . 

[arkmaker †]

Also, HPA needs more hammer hit (stronger spring) and a larger TP. Some of the HPA gurus will be along soon to help.

RIch

[UKStoo]

If the regulator is running at the 850 psi its supposed to, i expected to gain velocity. It could be that its running lower, i wont know until my asa adaptor comes and i can actually test the pressure.

Even if its lower i didnt expect to lose so much speed as the air should be more efficient.

With regard to the hammer spring, it shoots co2 fine at the pressures the reg is supposed to be outputting...theres no leaks that im aware of, i dont think the close velocity spread would be within 5 fps if there was a leak.

I may remove the non return valve in the quickfill nipple to see if thats causing the slow speeds but i doubt it

[UKStoo]

With a bit of jiggerypokery (thats tinkering, if you didnt know) ive tested the regulators output its giving 600psi! Not the 850 its supposed to be!

I calibrated the gauge ive attached to the asa on off valve against my stirrup pump and its accurate so i need to up the regulator output pressure.

When i can find how to do it!

[tinker]

What brand regulator?

Glen

[UKStoo]

Unknown brand, came fitted to a bottle i got off a mate, he ordered two new and sold me one at cost, he stated the regs to be set to 850 and the stack off washers definately matches all the info i can find for that output.

Trying to find where to buy belleville washers / springs in the uk that fit.

I know in the usa mcmaster carr sell them!

If needs be ill machine a washer for a spacer and up its pressure but thats last resort..

[quickster47 †]

Do you know if the regulator is a sping type or does it use shims, or the 'wave' washers to fix the regulator?

Carl

[UKStoo]

Its definitely a belleville stack, ive tinkered with it and swapped some round! Its gone up 50psi, some of the belleville washers look a little flatter than the others so ive set it like this for now.

|()()()()|

Thats the best i can get it with what i have.

[tinker]

Looks like you're on the right track.  The belleville washers can be a pain.  The regulators I have use the same system but also have a few flat washers which I think helps fine tune the output.  They are the last to be installed on the stack.  Sorry can measure them the bottles are all pressurized right now.

Glen

[UKStoo]

All sorted now, i machined a 1mm thick M8 steel washer to the correct od, removed one of the thinner spacers and added my custom version in its place and bingo 875 psi ish.

[arkmaker †]

So what FPS are you getting now??

[UKStoo]

So what FPS are you getting now??

I'll let you know when my new asa tank connector arrives, i used the original for the regulator pressure tester with a gauge and im waiting for its replacement in the post...

Im expecting it to be about 9 ft.lb with no other modifications, other than the lighter hammer spring.

[UKStoo]

Quick update....

The 1750 on hpa @ 850 is giving the same output as co2 now, 700fps, so the regulators low pressure is to blame. I expected a bit more than co2 powers though and may shim the regulator a little more...

I need to modify the asa adaptor though as its crap...

Last time i buy stuff like that from china again!