Fx amp regulator pressure shift with temperature

[Ignoto]

Hi guys, let me tell you right away this is not a reg creep situation.

I tested the accurate measure of the digital barometer directly affects the velocity.

I use a lot of different weight slugs and pellets and use the hammer wheel on the fx maverick to choose the best speed for each lead. I know the lighter ones are not at knee curve but as long as temperature doesn't change they print has they should. I have records on strelok for every best speed of each.

What bothers me is that i set those speeds at 25°Celsius wich corresponds to 170Bar but in a hot summer day the reg pressure goes to 160bar when temperatures are around 40°C. Again its not creep and reg is properly bedded. Tested through the afternoon when temperaure went progressively cool again and slowly back to 170bar. Kept shooting through as time passed and temp cooled.

I rolled my head around and the only thing that makes sense in my mind is thermal expansion of regulator piston being about 5x more than the body and Belleville's. I have polished both ends of piston and screw and successfully eliminated creep.
That's why i am now noticing this.
I will make a reg piston out of aluminium later and compare results unless anyone can explain me what other phenomenon could cause this.

 

[nervoustrig]

Yes Delrin has a significantly higher rate of expansion than the surrounding metal parts. When it elongates slightly at elevated temperature, the piston will reach the seat sooner and settle at a reduced pressure.

A new brass piston is becoming available according to some forum chatter so you may want to look into that.

That said, a 10 bar (140psi) difference centered around a 160 bar setpoint will produce no meaningful velocity change if the hammer spring tension is dialed to deliver about 97% of peak velocity.

How much velocity change are you seeing?

 

[Ignoto]

Thanks man! in fact i do recall some recent video showing some brass on new regs by fx just don't remember wich but i think it has something to do with rmac maybe by Giles from UK. If it is a simple replacement i might try it out.

With the 40gr velocity stands the same and when it happens i just turn the wheel 2 positions from 20 to 18 (custom hammer wheel i made) which means 0.7mm less hammer pre-load (the top velocity for 170 would be 1000fps but since i reduce it to the knee i should be 980 at position 20 and at 160bar is around 975fps at position 18). Higher just wastes air like that.

This is most critical with fx pellets 16 and 18gr wich are shot well below the knee and are so limited in accuracy at high speeds for the 18gr for example it shoots from 850 to a whopping high 900's.