Temperature vs Pressure

[C_cain_62]

I have only had my fx impact for a few months. When I got the gun it was about 90 degrees every day and it shot amazingly. I noticed the gun not shooting as well when the temperature got below 70 degrees. Fast forward to now, when the temperature can range 30 degrees from morning to afternoon I noticed that I could fill the gun when it was cold outside, and by the afternoon it would read to high on the pressure gauge, and if I filled it when it was warmer outside and it got colder the pressure would read lower than what I filled it to. I guess I have a few questions.

1: How do you keep the gun filled to the correct pressure without the risk of it over pressurizing when the temperature outside is fluctuating so much?

2: Do I need to adjust the setup of the gun to shoot better in colder temperatures?

 

[Guest]

The answer to both your questions is shoot more when the temp is going to increase or fill less. Shoot less when the temp is going to drop. Air pressure in a container will always change with temperature. As for how the gun shoots it shouldn't change much though your scope will/can shift it's point of aim considerably.

 

[Centercut]

Deleted

 

[fpgt72]

wow.....just wow....and not you OP.

First read this:

How does an air pressure regulator work?[/QUOTE]https://www.pyramydair.com/blog/2007/12/how-does-an-air-pressure-regulator-work/embed/

The regulator is a moving part....a machine inside the machine that is your rifle....that machines moving parts are going to react different as the temps change....it would be interesting to see chrono readings from warm to cold....I might do this experiment....but I would guess your fps readings are going to go wonky. All that air moving is going to make heat, with the outside being so cold, the parts that move in the gun your regulator is going to heat up and cool off...pretty darn quick....I bet you are going to see some nutty numbers....slow way down would be a suggestion.

As to the pressure spiking after the gun comes inside and warms up.....ever take a half full basket ball and put it in a car on a hot summers day with the windows rolled up....that is what you are doing.....going from warm to cold.

For your shooting session I would suggest having the equipment in the environment they are going to be used in, your fill bottle the gun...at 30f the pellet will even get harder....it works with water....metal tends to get softer when warm.

When you come inside and move the gun from the below ice cold weather to nice warm 72F house, the gun is going to warm up, parts are going to expand as the heat up.....you know the drill....have the pressure left in the gun be on the low side....that should take care of any over pressure you might see.

Sorry for being snarky.....but wow.

Oh and I never stayed at a Holiday Inn Express.

 

[sirk]

I hope these answer you questions. Real deal no theory. basically 20-30fps loss of speed (nothing major) barely visible on the POI.
copied the links from another forum, not mine videos hopefully ok to share

for the OP probably the loss of accuracy is unrelated to the cold.

 

[C_cain_62]

Thanks for the comments, as this is my first pcp, I am still learning.

 

[Guest]

If your cringe is for my comment oh well. I was a bit burnt out that day and if you read it it will make you want to know more or leave the subject all together. Or maybe make others post a reply to a question left hanging. Regardless it seems to have spawned one response that had to be deleted. Sometimes motivation comes in the oddest ways. I won't edit or remove it as I believe in leaving what I say for all to see, dumb, uniformed or straight up wrong no worries. Oh, scope shift can explain all of the issues.

 

[fpgt72]

You left so many holes in your comment.....sorry for being snarky.

I have those days too....more and more as I slide down the hill.....As I hang out here more I am sure they will become much more common.

 

[sirk]

there is lot of BS out on forums. with temperature only minimal change in pressure is present

see this calculation
here are some numbers, it works for Nitrogen like this
isochoric process becasue the container is constant volume (best approximation) personally i have not had my cylinder grow much LOL

P2=P1*(T2/T1)

P1=200bar=2E7 Pascal
T1=299.15Kelvin t2=26C=299.15Kelvin
T2=289.15Kelvin t1=16C=289.15K


P2=289.15/299.15=0.996*200bar=193.3



pressure goes down to 193.3bar from 200bar in container if you cool it 10degrees 



so not much change. co2 suffers more, because that is very specific

it is more the gun than the pressure effect.