Does the reservoir act as pseudo plenum when pressure drops below reg set point?

[UnderPressure]

Does the air reservoir act as a pseudo plenum when the air pressure drops below the regulator set point?

The reason I ask is because once the pressure in the reservoir falls below the set point of the regulator the regulator's check valve remains open and thus the air reservoir and plenum become freely communicating.

With the gun now operating as an unregulated one It would use air from the plenum plus be able to pull some (depending on the restriction) from the air reservoir since it is now no longer closed off to the plenum.

I am assuming any pseudo plenum effect would show up most when plenum size is small and valve dwell is large.

[nervoustrigger]

In the vast majority of cases, the regulator's aperture is too small to contribute any useful flow volume during the very short time the valve is knocked open.  For all practical purposes, the plenum remains the same size it always was.

[PikeP]

Mine...does... 4 mm hole is plenty of air flow

[AlanMcD]

Here is the test you can do to find out - vent the gun through the valve.  In an unregulated gun the air rushes out all at once.  In all mine regulated guns (admittedly all Humas) it takes several minutes to fully vent.  So I can say solidly in my case the answer is no.  And I don't think it matters how big the flow path is in the reg, it is about the spring stack and seal rod and how much air that can flow.

As a general rule, I would say the answer is no . . . .

[FuzzyGrub]

Watch the plenum gauge during the shot cycle.  If you see it drop and come back the answer is no. 

Some guns are restricted just by the regulator, but others are restricted even more ahead of it, such as the Liberty.  The passage through the block is around 2mm, but both ends feed through screw threads. 

I haven't experienced any high-flow regulators, but my experience has only been Huma, Milo74, Audrious, Crosman, and Nova Vista.  All of which are of a similar design using Belville washers/plunger.

[AlanMcD]

John's suggestion is a good one, as long as you are getting a decent amount of power out of the gun relative to the plenum size - if not, you might just be seeing the response time of the gauge (assuming it is on the plenum), which might not be very good.

I do know that with my Humas, the gauge drops a few hundred PSI and then climbs back up fairly quickly.  And also when I am shooting with the tank connected and the valve closed (so I can read reservoir pressure after the shot), there is no movement of the needle on the shot, but it drops the relevant amount in a quick few seconds after the shot (and I can hear the airflow).  When I do the same with unregulated guns, the drop on the tank gauge is much quicker and starts on the shot (it is an oil filled gauge, so it is damped) - I'd say instantaneous, but the gauge can't react that fast.

I assume there is no meaningful amount of air added to my plenums during my shot cycle . . .

[PikeP]

Do all the respondents to this thread have reading comprehension issues? He asked if the reservoir acts as a secondary plenum once pressure drops below set point....not during your normal shot cycle... (mine helps during both bttw...)


Yes, 100%. Once below set point, my reservoir is a secondary plenum in my setup. Additionally, any regulated rifle shooting below set point then needs to add their plenum volume into their efficiency calculations regardless if it works together with your reservoir once those two pressures equalize...

Regulators with small air flow pathways will not be able to flow enough air to act as a secondary plenum in any condition, but you will still have to calculate the plenum volume into the efficiency calculation for any shots below set point..

[nervoustrigger]

FWIW, the answer I gave was in fact to the question asked but it's just as valid for the normal scenario where reservoir pressure > plenum.
 
Simplest answer: a regulator with a large aperture will, a regulator with a small aperture won't.

[Ribbonstone]

Thinking you guys play in the fast end of the regulated pool....once it goes off reg, there is only a couple of shots before the pressure drops enough to be noticed.

On the slow end of speed, shooting like match speeds, it's hard to tell where it does go off regulation.  Using such a small amount of air from the regulated pletium, it pretty well acts like an unregulated rifle when it goes off reg. and you won't notice it being off reg. for quite a few shots.

So it doesn't act like a secondary plentium when it goes off reg....but if you weren't maxing out the normal plentium when it was on reg, you won't notice for quite a few shots.

Thinking of Bob's (rstern) "knee graphs"...sometimes you set it up to the left of the "best" on the graph....sometimes you set it up to the far right.

[PikeP]

I will make this rather simple.

The amount your reservoir acts as a secondary plenum, is directly proportionate to the refresh rate of the regulator, and how much air it can flow during your shot cycle, be it 1 ms, or 2ms...

Keep in mind, as your reservoir pressure changes, so does your refresh rate, as pressure is a variable of flow rate.

Regulator Refresh rate is calculated by the mass flow rate through the orifice of your regulator.

So the answer is yes, to any and all...but if you were to ask  how much pressure does the reservoir contribute to your shot cycle? Well...that answer could be 1 psi, or 500 psi, but you can take it to the bank, that no regulator out there, officially waits for your shot cycle to complete, and then says, okay time to now refresh, and not a nano second sooner...

[UnderPressure]

Thinking you guys play in the fast end of the regulated pool....once it goes off reg, there is only a couple of shots before the pressure drops enough to be noticed.

On the slow end of speed, shooting like match speeds, it's hard to tell where it does go off regulation.  Using such a small amount of air from the regulated pletium, it pretty well acts like an unregulated rifle when it goes off reg. and you won't notice it being off reg. for quite a few shots.

Ribbonstone the situation I am thinking about the most is Air Venturi Avenger where it develops its power from a ~5cc plenum at relatively high reg pressure.

[RayK]

... once the pressure in the reservoir falls below the set point of the regulator the regulator's check valve remains open and thus the air reservoir and plenum become freely communicating....

Are you sure this is how they work?  I would expect the regulator to also "close" when the pressure is equal on both sides of it (when off regulator) OR when the plenum pressure hits the regulated pressure (when on regulator).

Also, if the flow through a regulator can happen fast enough to allow the reservoir to act as a second plenum when off regulator, you would also see some effect of this flow on each shot while on regulator.

If my understanding is correct, the answer to your original question is "no."

Ray

[PikeP]

... once the pressure in the reservoir falls below the set point of the regulator the regulator's check valve remains open and thus the air reservoir and plenum become freely communicating....

Are you sure this is how they work?  I would expect the regulator to also "close" when the pressure is equal on both sides of it (when off regulator) OR when the plenum pressure hits the regulated pressure (when on regulator).

Also, if the flow through a regulator can happen fast enough to allow the reservoir to act as a second plenum when off regulator, you would also see some effect of this flow on each shot while on regulator.

If my understanding is correct, the answer to your original question is "no."

Ray

I cannot explain this much simpler than I already have...sooo

I will make this rather simple.

The amount your reservoir acts as a secondary plenum, is directly proportionate to the refresh rate of the regulator, and how much air it can flow during your shot cycle, be it 1 ms, or 2ms...

Keep in mind, as your reservoir pressure changes, so does your refresh rate, as pressure is a variable of flow rate.

Regulator Refresh rate is calculated by the mass flow rate through the orifice of your regulator.

So the answer is yes, to any and all...but if you were to ask  how much pressure does the reservoir contribute to your shot cycle? Well...that answer could be 1 psi, or 500 psi, but you can take it to the bank, that no regulator out there, officially waits for your shot cycle to complete, and then says, okay time to now refresh, and not a nano second sooner...

[UnderPressure]

... once the pressure in the reservoir falls below the set point of the regulator the regulator's check valve remains open and thus the air reservoir and plenum become freely communicating....

Are you sure this is how they work?  I would expect the regulator to also "close" when the pressure is equal on both sides of it (when off regulator) OR when the plenum pressure hits the regulated pressure (when on regulator).

Also, if the flow through a regulator can happen fast enough to allow the reservoir to act as a second plenum when off regulator, you would also see some effect of this flow on each shot while on regulator.

If my understanding is correct, the answer to your original question is "no."

Ray

https://www.pyramydair.com/blog/2007/12/how-does-an-air-pressure-regulator-work/

Without getting into design details, this is how an air regulator functions. As long as the air pressure in the reservoir is greater than the pressure setting for the reg, the reg closes after the regulated pressure has passed into the firing chamber. Once the reservoir pressure drops below the reg pressure setting, the reg never closes and the gun operates as an unregulated gun.

[RayK]

Your link actually proves my point.  The valve on that design is closed by the spring when the pressures on both side of the regulator are equal - even if the reservoir is below the regulator set-point.  I believe the author was simplifying his explanation for the masses when he said the valve never closes (it behaves as though the valve stays open).

"How does an air pressure regulator actually work?
The pressure regulator contains a powerful spring that acts on a valve. However, this spring is not powerful enough to keep the check valve closed against the high pressure of the air reservoir. Air forces its way through the check valve and into the firing chamber. When the pressure builds inside the firing chamber, it pushes on the check valve, helping the spring close the valve against the air reservoir. To control how much pressure is in the firing chamber, the spring is adjusted until the desired pressure closes the check valve."

[nervoustrigger]

I’m a few posts behind here but...

Pike is correct about there being some amount of flow through the regulator during the shot cycle, contributing to the plenum and thus affecting the average pressure during the shot.  It's of course the amount that matters.  (Hysteresis comes into play here as well but I wouldn't wager a guess as to typical amounts for the average AG regulator).  So I just want to describe for everyone why it's a behavior that is [almost] always desirable to minimize.
 
Before we move on though, I want to be clear we're talking about the normal case where we are still on the regulator.
 
So let's say we have a tune with a relatively small plenum for the desired energy level.  That means there will be a large pressure drop during the shot cycle.  The regulator's whole job in life it to respond to this pressure drop and open up and allow air through to try to maintain the plenum at the desired pressure.  If it has a large aperture, it can accomplish that goal quickly.  That sounds like a good thing, right?  Maybe, maybe not.  If the reservoir is at max pressure, there will exist a large pressure differential which means it will augment the shot more substantially than when the reservoir is at a lower pressure.  The result of that is an operating pressure that goes up and down with the reservoir...which is of course antithetical to what we want from a regulator.
 
Granted, whether or not that is significant enough to affect the ES a noticeable amount will depend on the particular circumstances (plenum size, state of tune, and the pressure delta between the max fill and the setpoint...just to name some of the big ones).  Regardless it's easy to see why it's not a behavior we would seek to maximize.
 
Unless.
 
Unless there isn't sufficient time between shots for the plenum to replenish.  So if the plenum is at risk of being starved, it would be a good thing.  That would be a consideration for a semi-auto, for example.  But for the vast majority of AG use, it is not a good thing.
 
One other thing about regulators with large apertures.  Large apertures mean large valve seats.  Large seats mean more opportunity for there to be an imperfection that causes pressure creep.  I'm not so sure it requires substantially tighter manufacturing tolerances to achieve the necessary perpendicularity because the spool has some forgiveness.  The O-rings seals that permit it to move axially also give it some measure of radial freedom.  But at the very least the two faces of the valve seat are ever more sensitive to flatness and surface quality the larger the seat becomes.  If the parts aren’t nigh on perfect, that has implications both early and late…a long break-in period and a short service life.
 
I hope this helps!

[nervoustrigger]

At rest, a regulator’s valve seat is open.  Meaning it wants to be open so to speak until such time as the pressure on its output side rises high enough to overcome the spring force that is holding it open.

[FuzzyGrub]

the situation I am thinking about the most is Air Venturi Avenger where it develops its power from a ~5cc plenum at relatively high reg pressure.

I just checked the Liberty reg spool.  2mm on the input, 3mm on the output.  As I mentioned before, the feed to the reg goes through two sets of threads, which restrict even more.  One is the air tube to block adapter, and the 2nd is the reg ext adjustment screw.  Huma regs typically have a "loose" screw on the input.  To me, it looks like they went out of their way to slow the fill down.

I re-looked at Red Target video for its version of the Avenger.  The reg block looks to be similar thickness to that of the Liberty.  Reg is oriented vertical vs horizontal of Liberty.  The reg cavity looks to be similar diameter.   I see some type of air tube adapter for the block.  Something on the adjustment side has changed.  But overall, I highly suspect that it has a very similar reg.   We won't know for sure until someone gets one and voids the warrantee. 

Now, we will be able to watch the plenum gauge during the shot cycle, which the oem Liberty does not come with.  The Liberty makes a drastic drop, recovers, and typically creeps for the next few minutes. 

[PikeP]

I’m a few posts behind here but...

Pike is correct about there being some amount of flow through the regulator during the shot cycle, contributing to the plenum and thus affecting the average pressure during the shot.  It's of course the amount that matters.  (Hysteresis comes into play here as well but I wouldn't wager a guess as to typical amounts for the average AG regulator).  So I just want to describe for everyone why it's a behavior that is [almost] always desirable to minimize.
 
Before we move on though, I want to be clear we're talking about the normal case where we are still on the regulator.
 
So let's say we have a tune with a relatively small plenum for the desired energy level.  That means there will be a large pressure drop during the shot cycle.  The regulator's whole job in life it to respond to this pressure drop and open up and allow air through to try to maintain the plenum at the desired pressure.  If it has a large aperture, it can accomplish that goal quickly.  That sounds like a good thing, right?  Maybe, maybe not.  If the reservoir is at max pressure, there will exist a large pressure differential which means it will augment the shot more substantially than when the reservoir is at a lower pressure.  The result of that is an operating pressure that goes up and down with the reservoir...which is of course antithetical to what we want from a regulator.
 
Granted, whether or not that is significant enough to affect the ES a noticeable amount will depend on the particular circumstances (plenum size, state of tune, and the pressure delta between the max fill and the setpoint...just to name some of the big ones).  Regardless it's easy to see why it's not a behavior we would seek to maximize.
 
Unless.
 
Unless there isn't sufficient time between shots for the plenum to replenish.  So if the plenum is at risk of being starved, it would be a good thing.  That would be a consideration for a semi-auto, for example.  But for the vast majority of AG use, it is not a good thing.
 
One other thing about regulators with large apertures.  Large apertures mean large valve seats.  Large seats mean more opportunity for there to be an imperfection that causes pressure creep.  I'm not so sure it requires substantially tighter manufacturing tolerances to achieve the necessary perpendicularity because the spool has some forgiveness.  The O-rings seals that permit it to move axially also give it some measure of radial freedom.  But at the very least the two faces of the valve seat are ever more sensitive to flatness and surface quality the larger the seat becomes.  If the parts aren’t nigh on perfect, that has implications both early and late…a long break-in period and a short service life.
 
I hope this helps!

Eh...square is square, true is true, and anything below nominal tolerances of said squareness and true-ness will result in creep, regardless of diameter. My knife edge is 4.5mm OD...and I have my creep down to roughly 2-3% (depending on how much I fill)...which is within what I would call the 'nominal sub 5% creep range'. The molecules trying to make their way pass your regulator seat are on the order of .0001 microns...

Really, this subject matter is a simple answer, but a complex solution to find out how much your regulator helps. For that, we would need to know the distance between seat and piston at your shots pressure differential and its smallest orifice (for example mine is roughly .25-.5mm lift on a 4mm seat depending on my power level..), your reservoir pressure (mine varies from 3450 to 1900, huge variance) including the differential between it and plenum, and your shot cycle time (mine is roughly .8 ms to 1.8ms depending on power level, and a difference of a 50 or 250 psi drop in the plenum depending on power level)...
 
In my findings, the difference between a regulator with a very restrictive orifice that marginally feeds your plenum opposed to a larger orifice that feeds your plenum enough to act as a partial auxiliary plenum, is noteworthy, even more so as you increase caliber or power output. The smaller the plenum is relative to your power output, the more noteworthy. Even in my configuration, with 53 cc, my peak output is currently 64 fpe at sub 2k regulated only because my plenum is partially fed by my reservoir during the shot cycle..if I were to plug my regulators feed holes to where the air flow was negligible, I would likely have a power output of 59 fpe being sub 2k psi regulated...

[nervoustrigger]

Yeah I think we're in agreement other than the ease with which achieving a suitably "creep-free" result can be obtained.  Creep is an illness with which I'm pretty well acquainted from having worked on a number of budget platforms.  I've honestly never had the pleasure of using a Lane regulator, for example.  Of course a big name doesn't inoculate one against it.  As you know, FX has a history of it.
 
Anyway I've seen plenty of examples of regs with both large and small apertures that want to creep, and for my modest skills at least, it has generally required more care and persistence to coax those with larger apertures to fall in line.  That's why I felt compelled to bring it up.  Certainly don't expect it to be the case 100% of the time.