Does it damage a PCP to dry fire it??

Forgive my ignorance, but would I be right in saying that it is air pressure in the cylinder that closes the valve after firing? In that case, pellet or no pellet, the same pressure will be behind the valve, closing it again.
 
Oldtime said:
hardairmagazine.com

Learn About How PCP Airgun Internal Ballistics Work

Internal Ballistics starts with a pellet at rest. When the gun is fired, air pressure acts on the base of the pellet, creating a force to accelerate it.
hardairmagazine.com hardairmagazine.com
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That article actually supports the opposite conclusion to what’s being suggested.

It shows the valve closes very early in the cycle, with the pellet only a short distance down the barrel (a few inches). After that point, the pellet is driven by expanding air and the pressure behind it is already dropping rapidly as the volume increases.

So there isn’t a stable “equal pressure on both sides of the valve” condition at closure. The barrel side is a dynamic, falling-pressure system, not a balanced one.

It also highlights that there is still residual pressure after the pellet exits (the muzzle report), which again shows the system is governed by expanding airflow rather than any kind of pressure equalisation.

In simple terms, the valve behaviour is dictated by reservoir/reg pressure and the spring, not by the presence of a pellet 🙂
 
JimJamJimmyJimmer said:
Forgive my ignorance, but would I be right in saying that it is air pressure in the cylinder that closes the valve after firing? In that case, pellet or no pellet, the same pressure will be behind the valve, closing it again.
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Yes mate you’ve got the right idea 👌🏻

It’s mainly the air pressure in the system (plus the valve spring) that closes the valve again after the hammer strike. The pellet isn’t what’s doing the closing.

The only small detail is that the pressure on the barrel side isn’t the same… it drops very quickly as the air expands… but that doesn’t really change how the valve behaves 👍
 
rockdrill said:
For such expensive guns they must use some pretty shite springs.
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Is that a statement or a question?
Either way, you are best referred to FX for comment as l can't because... l have no idea if they are shite or not.
 
Nitemax said:
Is that a statement or a question?
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Well if it was a question I would have put one of these ? at the end of the sentence instead of a full stop.

All I can say is in over 36 years of owning pre-charged guns and maintaining them I have never had one break a hammer spring, or any other spring for that matter.
 
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Gummage said:
Not 'that' kind of firing....mind you, perhaps on another thread for us oldies on here about potential damage caused by 'dry firing', I'm getting worried now🤔🥴
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**EVERYBODY PLEASE READ**

On a serious note lads, if you are dry firing it can be a symptom of prostate cancer. I understand volume diminishes as we age but very little or none at all needs checking out. It doesn’t mean you have cancer but if you do and it’s caught early I believe it is the most easily treated type of cancer. If left it might be the end of you so get yourself checked out!
 
Oldtime said:
The graph CLEARLY shows, what i have maintained all along, and that is, [when actually firing a pellet] that at the moment the valve closes, the pressure on both sides of the valve are about equal and so the valve closes quietly, unlike dry firing the thing when the valve will slam shut in a big way with vast pressure on one side and nothing on the other. it is CLEAR from the graph.
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Irrespective of who is right, the valve in my AEA weighs about 7 grams so I don't think 'slam' is the right word.
 
nikvanorton said:
Irrespective of who is right, the valve in my AEA weighs about 7 grams so I don't think 'slam' is the right word.
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The clos ing/ed force on that valve can be in the region of 400-700 lbs. And it goes to and fro in a few thousandths of a second. That sounds pretty vicious to me.
 
colinb said:
The clos ing/ed force on that valve can be in the region of 400-700 lbs. And it goes to and fro in a few thousandths of a second. That sounds pretty vicious to me.
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I would dispute that, quite simply because a hammer that weighs a few grams and accelerated from as little as 7mm away can open it against the closing force of whatever the anything from 60bar upwards applies, don't forget that the closing force is applied to a small area from as little as 6mm, so the actual force is much diminished.
 
An unregulated pcp is a basic bias valve.

The spring is not there to provide resistance when the gun is pressurised, it is there to provide direction of rest.

The pressure systems we make at work use pulsed valves to control pressures north of 90,000 psi.

ALL kinetic impacts cause stresses to form and deform. When a hammer strikes it is trying to overcome resistance of the air pressure, spring, drag, and friction.

Spring, drag and friction are irrelevances with numbers so small they only change 3rd and 4th decimal places in a flow dynamics equation. (You REALLY don’t want to have to do those equations as part of your job)

Synopsis ?

An empty guns valve system will suffer more damage than a part filled, a part filled will suffer more damage than a fully filled.
A fully filled will still suffer damage but to a degree that is is considered “nominal wear”.

It’s the same mechanism of damage that an air cylinder on a pcp is subject to, filling a pcp cylinder from empty to full will cause more “creep” than filling from 150 to 300 bar.

Anything more than firing a pcp empty or near empty is just mathematical semantics.
 
Yes my AP40 requires you to empty the air tank before taking it off, so yes its ok to dry fire (at least i hope it is).
 
Tricky-Dicky said:
I would dispute that, quite simply because a hammer that weighs a few grams and accelerated from as little as 7mm away can open it against the closing force of whatever the anything from 60bar upwards applies, don't forget that the closing force is applied to a small area from as little as 6mm, so the actual force is much diminished.
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If you assume 300 bar or 4500psi. The valve total area on that side, parallel to the valve seat, might be as much as 0.1 sq inch. So 450 lbs. Yes my 700 is a bit on the high side. Neglects any force from the EV spring.
 
colinb said:
If you assume 300 bar or 4500psi. The valve total area on that side, parallel to the valve seat, might be as much as 0.1 sq inch. So 450 lbs. Yes my 700 is a bit on the high side. Neglects any force from the EV spring.
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That’s a dirty great big valve
And running at 300 bar ?

Blimey

More likely numbers are
Let’s say for convenience 1/4 inch valve hole (6.25ish

At 1500psi ( 100ish bar )
 
Actually just found an area x force calculator and 80/1200psi over an area of 6mm sq (this is larger area then the real size of most valves) results in 111.6 lbs force, as I said all along it's nowhere near as much as people think, I have emptied guns of air by removing the hammer and either tapping or pressing the valve with a metal rod on many occasions, if it needed 400lbs to 700lbs I wouldn't be able to do this, try it for yourselves, Ok on a non regulated guns it's going to be somewhat more, but if you notice on an unregulated gun the valve area is usually pretty small and also the return spring is weaker as this is also a factor.
 
Never had any issues with dry firing my fx impact m4.

First huma reg set at 120 bar, 2nd huma reg set at 50 bar.
🤣🤣
 
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Oldtime said:
Absolutely YES. Try this simple experiment.

1, Wait for a windy day.

2, Open your front door wide.

3, Go open your back door.

4, See how your front door has slammed violently shut and you are lucky if the glass has not fallen out???

So it is with valves..

Doing it without air, is just as bad, but for a different reason.
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I had to chuckle at this simple experiment. I don't know why but it tickled me.
 
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