Spring vs. Gas Piston. Is it really a big deal?



Author Topic: Spring vs. Gas Piston. Is it really a big deal?  (Read 22214 times)

Offline Makincheez

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Re: Spring vs. Gas Piston. Is it really a big deal?
« Reply #20 on: May 03, 2011, 02:49:21 AM »
Michael, I believe that is correct. My thinking is that in cold weather the piston seal contracts more than the chamber, and any lube on it gets more viscous , so you lose some velocity. I couldn't tell you at what temperatures this would be a factor. (please, tell us more Mr Science) ok, I'll shut up now...... ;)
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Offline Jay

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Re: Spring vs. Gas Piston. Is it really a big deal?
« Reply #21 on: May 03, 2011, 02:54:38 AM »
From what we have discussed on here Michael they seem to loose just a bit in cold weather(20 or so fps), we have never really came up with if its the nitrogen in the piston or just the colds effect on steel,lubes an other factors in the guns same as on a springer really. Guess we need someone to take a piston an check compression weight in warm an cold so we can have a positive answer to end the debate. Anybody got a spare around an the time?
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Wampus

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Re: Spring vs. Gas Piston. Is it really a big deal?
« Reply #22 on: May 03, 2011, 10:26:25 AM »
All gasses change pressure with temp change if volume is held constant.  Nitrogen is no different from oxygen in that regard.  Air is about 78% nitrogen anyway.  The reason pure nitrogen is used in the pistons is bcause it dosen't oxidize the materials and it's moisture-free.  Water changing from liquid to vapor and back again has a big effect on pressure so a very dry gas is critical.  Nitrogen is just readily available, cheap, and inert, but it absolutely will lose pressure as the temp drops and increase pressure as the temp rises.
« Last Edit: May 03, 2011, 10:32:09 AM by Wampus »

airiscool

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Re: Spring vs. Gas Piston. Is it really a big deal?
« Reply #23 on: May 03, 2011, 01:40:38 PM »
Arn't the gas rams filled with nitrogen which is not suppose to change pressure due to changing temperature?

Despite what the gun manufacturer's advertisements say, nitrogen is affected by temperature changes.

When this topic last came up a couple months back, I wondered if nitrogen was an exception. Knowing they fill nitrogen tanks for welding uses, and they store their tanks in unheated sheds, I called my welding gas supplier to double check. He said what Wampus just said, all gases shrink/expand with temperature changes. 

There's nothing unique about nitrogen when temperatures change, it changes pressure just like other gasses.

And, since they both use them, any temperature change that affects seals and lubes will do so with coil spring or gas ram. So that's pretty much a wash. The biggest change in pellet speeds is from temperature affecting gas pressure.
 
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michael word

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Re: Spring vs. Gas Piston. Is it really a big deal?
« Reply #24 on: May 04, 2011, 02:04:33 AM »
Thank you everyone for clearing the up for me.

Offline oldpink

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Re: Spring vs. Gas Piston. Is it really a big deal?
« Reply #25 on: May 04, 2011, 02:56:23 AM »
As was pointed out, all gases are affected to some extent by temperature changes, some more than others, and certainly nitrogen is less affected than compressed air.
Also, while gas rams are affected by temperature change, they seem much less so than spring guns, and it takes a much greater temperature drop to see that change.
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rbshoots

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Re: Spring vs. Gas Piston. Is it really a big deal?
« Reply #26 on: May 04, 2011, 05:46:17 AM »
not all.....the theoben rams are air filled and are made so the user, with the pump sold for the ram, can adjust the pressure in the ram to suit the users need.....they are however the upper end of the price spectrum

Online uncle paulie

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Re: Spring vs. Gas Piston. Is it really a big deal?
« Reply #27 on: May 04, 2011, 07:53:25 AM »
Maybe its just the guns themselves that underperform in the cold. At any rate, under 30deg. I make sure to keep mine warm......in the basement! ;)

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zzyzx

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Re: Spring vs. Gas Piston. Is it really a big deal?
« Reply #28 on: May 04, 2011, 10:32:38 AM »
At 15-40 below zero you are so chilly you slow down a bit and really don't notice the rifle doing so.  ;-)

Offline lloyd-ss

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Re: Spring vs. Gas Piston. Is it really a big deal?
« Reply #29 on: May 04, 2011, 01:15:17 PM »
The nitrogen springs are pretty cool and have many pros, and a couple of cons.  But steel  springs will be around for a long time!

These nitrogen springs are basically VERY specialized nitrogen die springs that have been used in industrial stamping dies for many years.  The environment is brutally harsh and the springs are often cycled faster than once a second and last through 100s of thousands of cycles.  Here's a link for some nitrogen die springs. They come in different lengths and diameters and forces:
http://www1.mscdirect.com/eCommerce/SearchServlet/Motion-Control-Fluid-Power/Shock-Absorbers-Springs/Springs/Nitrogen-Gas-Springs-Accessories/Nitrogen-Gas-Spring-Cylinders/_/N-77g61Z1yzlvnf?refinement=4292439694&searchandizedOk=Y&currentMSCtt=nitrogen+die+spring&currentRawInput=nitrogen+die+spring%A2nitrogen+die+spring&currentMSCtk=All_MSC&currentMSCtx=mode+matchallpartial

Regarding the temperature affecting the gas pressure, that is true.  For an ideal gas, which nitrogen is (and air is not), the change in pressure is proportional to the change in temperature PER DEGREES KELVIN, in other words, related to ABSOLUTE ZERO, which is minus 460 degrees F.  If a gas spring drops from 90F to 20F its internal pressure could drop up to 13% but some are designed with temperature compensation. (Speaking about nitrogen die springs).  Cold temp also affects lubes and seals and people.

BUT in a springer, that 13% internal pressure drop will result in a LOT LESS THAN 13% velocity drop.  Increase in pellet velocity is not usually directly proportional to increase in spring pressure, whether its a nitrogen spring or a metal spring.

Just my 2 cents.
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